摘要:

APPENDIX. A TABLE OF DIPOLE MOMENTS. This is a catalogue of dipole moment data which have largely been The following information is given in respect of each substance :-I. The moment. 2 . The temperature or temperature range in "C. 3. The solvent or the medium in which the measurement was carried out. 4. The method used for eliminating PE :-" Opt." indicates the refractive index method ; " T," the temperature variation method ; " Solid," by determining the dielectric constant of the solid. 5 . If allowance has been made for atom polarisation the symbol PA is inserted. If it has been assumed by the author that PA is 15 per cent. of PE the symbol PA 15 is used. 6. The observed value of COP (if it is given by the author) the mole-cular polarisation at infinite dilution under the conditions already specified in columns 2 and 3.7. The name of one author responsible for the determination and the reference to the bibliography (see pp. ii to ix). Except in the very small number of measurements by the beam method the procedure always involves the measurement of the total molecular polarisation COP, and the subtraction from this of the electron polarisation PE and sometimes also of the atom polarisation PA. In the optical method PE is derived from the refractivity which is sometimes determined experimentally and sometimes calculated from the values for the atoms. PA may be determined experimentally (e.g. by the temperature variation of COP or from the dielectric constant of the solid) or may be calculated by various theoretical methods for which the original papers must be consulted. When allowance has been made for PA by these theoretical methods the value of the moment when no allowance is made is also given. The classification of the substances is a slight modification of that employed by Richter and is as follows :-collected by Dr. N. V. Sidgwick.

ISSN:0014-7672    

DOI:10.1039/TF93430BB00i

出版商:RSC    

年代:1934

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.

ISSN:0014-7672    

DOI:10.1039/TF93430FP001

出版商:RSC    

年代:1934

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. INTRODUCTORY ADDRESS. “FREE RADICALS AND IONS AS FACTORS IN CHEMICAL CHANGE.” BY PROFESSOR T. M. LOWRY, F.R.S. The General Discussion on “ Free Radicals ” which I invited the Faraday Society nearly two years ago to hold in my laboratory, was arranged primarily in order to direct attention to the important part which these usually-unstable aggregates of atoms may play in chemical reactions, and to the physical methods by which their presence may now be detected and proved, under conditions in which a few years ago their existence was a mere speculation.The time is particularly opportune for such a discussion in view of the large amount of attention which has been given to the ionic theory of organic reactions during the present century and especially during the past twelve years. For this purpose I may remind you that the earliest general theories of chemical change were dualistic and elec- trochemical in character, since they were based mainly upon the pro- perties of inorganic substances in general and of electrolytes in particular ; but the error which Berzelius made, in attempting to explain the structure of organic compounds by means of his dualistic theory, was repeated by the organic chemists from Dumas onwards, who were brilliantly successful in developing a unitary theory of molecular structure, and in applying i t to organic compounds of the most complex types, but who failed to appreciate the large element of truth which remained in the dualistic theory which they had brought to the ground. It is indeed remarkable that, during the latter half of the nineteenth century, when structural organic chemistry was developing more rapidly than any other branch of the subject, valency seems to have been thought of exclusively in terms of bonds, and no clear distinction was drawn between the structures of such unlike substances as the alcohols and alkalies or the esters and salts, since these were represented by symbols of identical type, e x .9 K-0-H K-Cl CHS-0-H CHS-Cl. An important advance was made when Arrhenius in 1883 developed the theory of reversible ionisation, as expressed by equations such as + - + K-Cl S K + C1 KOH + K + OH. It is customary at the present time to disparage this contribution to chemical theory, mainly because the theory of complete ionisation has postulated that ions are already pre-existent in solid salts, so that the ionising solvent is not responsible for producing the ions, but only for separating them to such an extent that they can move indepen- dently under the influence of an electrostatic field. Whilst, however, the quantitative aspects of the theory have been shown to be wrong, at least in the case of strong electrolytes, real importance still attaches 34 FREE RADICALS AND IONS to the general conception that (in more modern terms) a covatmt molecule may be resolved into ions, and that (as J.J. Thomson and Nernst pointed out) this process takes place most readily in a medium of high dielectric constant, where the molecules of the solute are exposed to the influence of solvent molecules with large dipole moments. Thus Arrhenius’ con- ception of reversible ionisation is perfectly correct when applied, for instance, to the salts of mercury, the crystals of which have been shown by X-ray analysis to consist of covalent molecules and not of aggregates of ions. We can, therefore, represent the ionisation of mercury salts by reversible equations, as follows :- - ++ - The same conception is equally valid when applied to the acids, although the evidence for the hydration of the ions is here much more obvious and important, H,O + HCl + H,O + El.+ The extension of these ideas to typical organic compounds was made a t the junction of the two centuries by Euler and by Lapworth. Thus in 1899 Euler attributed the hydrolysis of an ester to its dissocia- tion into ions, CH, . CO . OC,H, f CH, . CO . 0 + CzH,. Catalysts were supposed to act by increasing the velocity of ionisation, rather than by displacing the position of equilibrium in this balanced action. In general he considered that there were no grounds for making a distinction between electrolytes and non-electrolytes, and that all chemical substances might therefore be regarded as electrolytes. At the present time the contrast between molecular and ionic lattices has provided a new method of distinguishing between molecules and ions in the solid state, and few of us would be prepared to follow Euler in minimising the difference between electrolytes and non-electrolytes.Moreover, the simple ionic mechanism which he suggested has been superseded by one according to which the ester first becomes associated with a hydrogen or hydroxyl ion, on the one hand, and with a molecule of water on the other hand ; the complex thus formed then undergoes a sort of ionic dissociation, in the course of which an unsymmetrical or ionic fission of the bond between carbon and oxygen leads to the resolution of the ester into acid and alcohol,Z and a t the same time liberates a hydrogen or hydroxyl ion for further service as a catalyst.Euler was, however, obviously correct in postulating an ionic mechanism for a reaction which can only take place in presence of water and is catalysed by hydrogen and hydroxyl ions, even though the principal reactant is a typical organic compound. who stated in 1901 that he had ‘‘ held for a long time ” the view that it is to electrolytic dissociation, often doubtless in extremely minute amount, that the majority of changes in organic compounds may be most probably assigned. This IEuler, Abstr., ii, 532. 1900; Ber., 33, 3202, 1900 ; 2. physikal. Chem., 36, 641, 191. * See T. M. Lowry, “ An Electrolytic Theory of Catalysis by Acids and Bases,” International Conference of Physical Chemistry, Paris, I 928, 8Lapworth, J .Chcem. Soc., 79, 1266, 1901. A similar suggestion was made by LapworthT. M. LOWRY 5 mechanism was used to provide an explanation of the “ Intramolecular Changes in Organic Compounds,” which he had classified with marked success in 1 8 9 8 ~ into the as and ay-types. Here again subsequent investigations 5 have established the correctness of the ionic point of view by showing that the ay-type of prototropic change is catalysed by ions or molecules which are donors or acceptors of protons, and can only proceed with appreciable velocity if both types of catalyst (acid and base) are present in an amphoteric medium. Similar conclusive Lvidence of the validity of Lapworth’s ionic theory of organic reactions was supplied by his proof that the cyan- hydrin reaction does not proceed by the addition of molecules of hydrogen cyanide to the aldehyde or ketone, but is dependent on the addition of cyanide ions to the carbonyl radical In this reaction the organic molecule is not resolved into free ions ; but the process can be explained most readily by postulating a polar activation of the carbonyl group, with formation (under the influence of the ions of the reagent) of a mixed or semi-polar double bond,’ thus ‘C=O + EN -+ \&-O + CN -+ \C-6 - - / / ’I CN The developement of the electronic theory of valency has contrj- buted largely to the popularity of the ionic mechanism of organic re- actions by providing a clear picture of the conversion of a convalence into an electrovalence as depending on a one-sided distribution of the two shared electrons of the ruptured bond,-a reversal of the process whereby the dative bond of Menzies (or the co-mdinate link of Sidgwick) is formed by sharing two electrons belonging originally to a single atom, molecule or ion; and in view of the importance which I have attached to the process of “ Intramolecular Ionisation ” I do not think that I can be accused of any lack of interest in this aspect of the problem of organic reactions.I have, however, deliberately proposed, and helped to organise, the present discussion, in order to emphasise the fact that there is a second mechanism whereby organic reactions can proceed, namely that in which a molecule is resolved into two elec- trically-neutral radicals.This mechanism is fundamentally identical with that which organic chemists have used during the greater part of a century, since until recently the replacement of hydrogen by halogens, nitro-groups or sulphonic radicals was always formulated as depending on an interchange of a neutral atom of hydrogen for an equally-uncharged radical of the substituent. It is, however, nearly obsolete as regards reactions of this type, in view of the evidence provided by Lapworth, Mi. A. Noyes, Robinson, Conant, Ingold, Bennett and others, that re- agents from which ions are so readily produced, and reactions which are J . Chem. Soc., 73, 445, 1898. Lowry and Faulkner, J . Chem. Soc., 127, 2883, 1925. J . Chem. Soc., 83, 995, 1903.Trans. Faraday SOC., 18, 285, 1923. 7 Lowry. “ The Polarity of Double Bonds,” J . Chem. Soc., 123, 8 2 2 , 1923.6 FREE RADICALS AND IONS so much influenced by the distribution of positive and negative poles must be essentially polar or ionic in character. Nevertheless, it is becoming increasingly clear, mainly from the work of physical chemists, that there are many organic reactions in which the traditional conception of chemical change proceeding through the formation of neutral radicals can be justified by new evidence of a more conclusive character than the indirect arguments formerly employed, Direct evidence of the non-ionic fission of molecules was provided in the first instance from the study of gases. Thus it was shown that iodine-vapour has no marked electrical conductivity at high temperatures, when its vapour density has fallen to one half of the normal value for molecules of I, ; these molecules must therefore have dissociated into neutral atoms and not into oppositely - charged ions.Similarly, Bodenstein was obliged to abandon an ionic chain mechanism for the interaction of hydrogen and chlorine, in favour of a mechanism depending on neutral atoms. Indeed, the work of Bodenstein, Berthoud, Hinshelwood and Norrish indicates clearly enough that gaseous reactions normally proceed in this way, and that ionic reactions are the exception and not the rule so far as gases are concerned. The electronic theory has not only provided a clear picture of the resolution of molecules into ions, by the unsymmetrical distribution of the shared electrons of a bond, but with complete impartiality has provided an equally clear picture of the resolution of a molecule into free radicals by the symmetrical rupture of a bond, in which the two shared electrons are distributed equally between the two atoms which they formerly united.The electronic theory has therefore given pre- cision, not only to the view that there are two types of valency, depending on electron-transfer and on electron-sharing, but also to the view that there are two ways in which molecules may undergo chemical change, namely (i) by the symmetrical rupture of a bond with formation of two neutral uncharged radicals, and (ii) by the unsymmetrical rupture of a bond, with formation of two oppositely charged ions, or in the case of a multiple bond (where only one link is ruptured), of a bipolar molecule or pair of “ bound ions.” Three methods can then be used to determine by which type of mechanism a particular reaction proceeds. (a) Kohlrausch, from the physical side, and Werner from the chemical side, recognised that the formation of free ions in aqueous solutions depends on enveloping the charged atoms or radicals with a “watery atmosphere” of the solvent. An ionic mechanism may therefore be suspected for all those reactions which proceed most readily in aqueous solutions, or in an ionising solvent, whilst those which occur in gases, and some of those which occur in liquid media of low dielectric constant, rpay, in the absence of evidence to the contrary, be expected to proceed by the formation of neutral atoms or radicals.(b) An ionic mechanism can obviously be attributed to (i) all reactions, such as the cyanhydrin reaction, which are brought about by the ions of a reagent, (ii) all reactions, such as hydrolysis and prototropic change, which are catalysed by ions, (iii) many, if not all, reactions which are promoted by a polar environment, e.g., the interaction of ethylene with s Bodenstein, 2. fihysikal. Chem., 85, 329, 1913 : 2. f. Elektrochemie, 33, $3, 1916 ; Nernst, ibid., p. 62, 1918 ; 34, 1916 ; Warburg, Sitzungsbev. Pveuss. Akad., p. 314, 1916; p. 300, 1918.T. M. LOWRY 7 chlorine or bromine when in contact with wet glass.1° On the other hand, the majority of photo-chemical reactions and of thermal de- compositions appear to depend on the formation and interaction of neutral free radicals. Thus the nuclear substitution of toluene, in presence of a halogen-carrier such as ferric chloride, probably proceeds by an ionic mechanism, whilst substitution in the side chain under the influence of sunlight probably depends on the action of neutral atoms of the halogen.( c ) W. A. Noyes and Robinson, amongst others, have pointed out that when a molecule of a halogen is ionised it yields one reactive positive ion and an inert negative ion, e.g., the action of potassium hydroxide on chlorine may be formulated as follows: +- KOH + C1, + k + el& + OH + k e l + ClOH where the negative chlorine ion is a stable bye-product of the interaction of OH with C1 to form CIOH. On the other hand, the non-ionic fission of the molecule gives rise to two reactive atoms, the formation of which can often be established by the fact that the reaction-velocity is pro- portional to the square root of the concentration of halogen.ll For the purpose of the present discussion we may use a paraphrase of the definition given by Wieland l2 in 1915, as follows: ” Free radicals are complexes of abnormal vabncy, which possess additive properties, but do not carry an electrical charge and are not free ions.” Most of the free radicals referred to in the papers now to be dis- cussed possess one free unsatisfied vaIency.This is true for instance in the case of the hydrogen, oxygen and hydroxyl radicals discussed by Harteck, of Paneth’s methyl and ethyl radicals and of organic radicals of the triphenylmethyl type discovered by Gomberg and dis- cussed in Ziegler’s paper.These aggregates contain an odd number of electrons, so that one electron is necessarily unpaired and gives rise t o paramagnetism, as Sugden has shown in certain typical cases. This criterion can be used to justify the inclusion in the category of free radicals of all molecules which possess an odd number of electrons, including some which are completely stable. I t would indeed be illogical to include Gomberg’s C10, and Bodenstein’s ClO, in the category of free radicals, because they are difficult to prepare, and to exclude the more familiar C10,. For the purpose of classifying chemical reactions also it is obviously necessary to include NO and NO, with the metals of the alkalies amongst the “ odd-electron reagents.” l3 The possession of an odd number of electrons, however, is not an essential characteristic of free radicals, since there is no reason why unsatisfied valencies should not appear a t two points in the same mole- cule.In most cases this is only possible when these two points are not contiguous, since otherwise the unsatisfied valencies will usually satisfy one another, giving rise to a multiple bond. The products are still described as “ unsaturated ” ; but compounds containing multiple bonds 10 Norrish, J . Chem. SOL, 123, 3006, I923 ; 55, 1926 ; Gwyn Williams, ibid., 1747 and 1758, 1932. 11 Hertzfeld, Ann. Physik., 59, 635, 1919 ; Bodenstein and Liitkemeyer, 2. fihysikal. Chem., I 14,208.1g24 ; Berthoud and Bellenot, J .Chine. physique, ar, 308, 1924. 12 Wieland, Ber., 48, 1098, 19x5. l3 W. A. Noyes, J . Amer. Chem. SOC.. 50, 2902, 1928 ; 53, 2137, 1g3x ; R. Kuhn, Solvuy Refiort, p. 365, 1931. +FREE RADICALS AND IONS do not usually possess either the physical or the chemical properties of typical ” free radicals ” and are therefore excluded from this category. This exclusion can be justified by the absence of paramagnetism. since this provides direct evidence that all the electrons are paired, On the other hand, the paramagnetism of oxygen shows that it contains two electrons with unneutralised spin-moments, and the classification of molecular oxygen with the “ free radicals ” is considered in Steiner’s contribution to the present discussion. Another free radical with an even number of electrons, and obviously related closely t o molecular oxygen, is sulphur monoxide, which forms the subject of a paper by Cordes and Schenk.In the organic group, the methylene radical, which Belchetz has detected as a product of decomposition of methane, also contains an even number of electrons; but it possesses all the properties of a free radical, since the relatively-saturated character developed in carbon monoxide appears to be incapable of development in compounds of bivalent carbon with univalent elements such as hydrogen and chlorine in the radicals CH, and CCl,. An interesting application of the general rule that even numbers of electrons are characteristic of stable molecules, whilst odd numbers are characteristic of free radicals, is provided by Conrad’s study of the decomposition products of hydrocarbons in the “ canal-ray tube.” Since the mass spectrograph will only detect positively-charged particles, all the radicals detected by this method have been robbed of an electron.Hydrocarbon radicals containing an odd number of hydrogen atoms therefore contain an even number of electrons and are more abundant than radicals containing even numbers of hydrogen atoms but odd numbers of electrons. The free radicals now under discussion fall naturally into two main groups. Those of relatively long life, which can be prepared and studied by ordinary chemical methods will be considered first. Free radicals of the triphenyl-methyl type, discovered by Gomberg in 1900,14 have been prepared in large numbers during the subsequent years, as may be seen from the reports on “ Radicaux Libres ” contributed by Walden to the Third Solvay Conference in 1928, and by Schlenk to the Fourth Solvay Conference in 1931.No attempt has been made to duplicate the substance of these reports for the purpose of the present discussion ; but this type of free radical forms the subject of papers by Ziegler and by Huckel, who have discussed from the chemical and physical standpoints respectively the reason why the central bond of hexaphenyl- ethane is so easily ruptured. Inorganic radicals of long life are re- presented by Gomberg’s perchlorate radical and by the sulphur mon- oxide of Cordes and Schenk, whilst Steiner’s paper deals with molecular oxygen as a free radical.The reason why some radicals are stable and others are not is discussed by Goodeve for aggregates of three atoms, as well as by Huckel for hydrocarbon radicals. Free radicals of short life have often been postulated as intermediate products of chemical change. Thus Bone and Coward in 1908 l5 in a paper on the “ Thermal Decomposition of Hydrocarbons ” such as C,H, C,H, and C,H, found it necessary to postulate that “ the primary effect of high temperatures is to cause an elimination of hydrogen with a simultaneous loosening or dissolution of the bond between the carbons, giving rise to residues such as : CH, and : CH.” They also gave conclusive 1‘ Ber., 53, 3x50, 1900 ; J . Amer. Chem. SOC., 22, 757, I-. 15 Bone and Coward, J . Gem. SOC., 93, 1197-1225, 198.T.M. LOWRY 9 experimental proof of the hydrogenation of such residues to CH,. The present discussion includes a contribution by Bone on “ Free Radicals as products of the Combustion and Thermal Decomposition of Hydro- carbons,” together with papers on other aspects of the same problem by F. 0. Rice and by Belchetz. Exceptional interest attaches to Paneth’s isolation of methyl and ethyl radicals as products of decomposition of lead tetra-methyl and tetra-ethyl.ls Although these radicals may have a life of only about 0.006 seconds it has been possible to use them in synthetic work. Thus in his contribution to the present discussion, Paneth describes the synthesis of the antimony-analogue of Bunsen’s historical “ cacodyl radical,” Me,Sb . SbMe, compare Me,As .AsMe,. The formation of free hydrocarbon radicals is also discussed by Polanyi, who has prepared them by the action of sodium vapour on the vapour of alkyl iodides, and by Norrish, who has eliminated carbon monoxide by the photochemical decomposition of aldehydes and ketones and ob- tained condensation-products of the remaining alkyl-radicals or hydrogen. In a paper by Dhar, it is suggested that hydroxyl radicals are formed by the action of sunlight on water and play an important part in photo- synthesis. The physical evidence for the existence of free radicals of relatively short life is largely spectroscopic in character, since free radicals may give rise to characteristic absorption bands in solution, or to band spectra with a characteristic fine structure in gases or vapours. The existence of free radicals under less placid conditions may also be disclosed by means of emission spectra consisting of bands instead of lines, e.g., the “ Swan bands ” of carbon, the “ steam bands ” of Liveing and Dewar, or the “ Schuster bands ” of ammonia. This aspect of the problem of free radicals forms the subject of an important report by Mecke; but emission-spectra are also included in the contribution of Willey, who discusses the formation of free radicals in the electric discharge, with special reference to the radicals CH, NH and OH. In more general terms, Semenoff discusses the conditions under which the intermediate products of chain-reactions may perhaps be detected by spectroscopic methods. Two other physical methods will be referred to in the discussion, since the possibility of demonstrating the electric and magnetic moments of free radicals by the method of molecular rays will be discussed by Fraser, whilst Aston will give a demonstration to show how positively charged radicals may be detected by means of the mass-spectrograph. A similar denonstration of the formation in the canal-ray tube of hydro- carbon radicals of diverse degrees of unsaturation will be given by Conrad. The papers already contributed cover a very wide range, and the presence of so many of the leading workers on the subject is a sufficient guarantee that they will give rise to an interesting and important dis- cussion. 16 Paneth and Hofeditz, Ber., 62, 1355, 1929 Paneth and Lautsch, Ber., 64, 2702, 1931.

ISSN:0014-7672    

DOI:10.1039/TF9343000003

出版商:RSC    

年代:1934

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. LEGACY TO THE FARADAY SOCIETY. The late Lieutenant-Colonel Bourke, who was a founder member of the Faraday Society, died a t his residence a t Hertford on the 22nd of November, 1933, aged 68 years. By a will made the 6th July, 1933, he appointed his bankers as Executors and Trustees and, after leaving certain sums to servants and friends, bequeathed all his real and personal estate to his bankers to hold the same upon trust for the Faraday Society, London, absolutely. This bequest was made with the request and in the confidence (but without imposing any legal obligation) that the Society will use the same for such purposes as the Society may consider best fitted to advance human knowledge. The amount of the legacy accruing to the Society cannot yet be accurately stated, but it should exceed EIO,OOO. The Society had no knowledge whatsoever of the intention of its generous benefactor, and Members will feel deep regret that the Society was not able during his lifetime to express thanks to its late member.

ISSN:0014-7672    

DOI:10.1039/TF934300X004

出版商:RSC    

年代:1934

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. OBITUARY. LIEUTENANT COLONEL JOHN JOSEPH BOURKE, I.M.S., C.I.E.1865 TO 1933. Lieut.-Col. Bourke was born a t Kilkea, County Kildare, on 1st April, 1865, the son of Michael Burke of Kilkea. Nothing is a t present known of his boyhood life, but it has been ascertained that in October, 1883 (as Mr. Bourke), he passed the First University Examination of the Royal’ University of Ireland, and in September, 1884, the Second University Examination. In both these examinations he took Honours in Ex- perimental Physics. He graduated B.A. in 1885 and obtained the degree of Master of Arts in 1886. He then proceeded to study medicine a t the same University, taking in October, 1891, the degrees of Bachelor of Medicine, Bachelor of Surgery and Bachelor of Obstetrics. For the last-named degree he studied also at The Coombe. In 1890-1891 he was awarded a Final Exhibition in the Medical School of the Catholic University of Ireland.On the 30th January, 1893, he received a commission as Surgeon- Lieutenant in the Indian Medical Service. After a period of general medical service, whilst engaged in 1897 on plague service at Itarsi, h e was invited to join the Chemical Department as probationer and was directed to proceed to Madras. From May, 1898, to October, 1899, he was acting Chemical Adviser to the Government of Bombay, now holding the rank of Captain. In 1899, on the return from sick leave of the officer for whom he was acting, he applied for permission to proceed to Europe for two years on special leave, to study the developments in chemistry which had arisen in recent years. He offered to devote a year’s furlough to this study if his full request could not be granted.The Surgeon-General in endorsing his application paid tribute to his efficiency and ability. The request was, however, not granted. Nevertheless he devoted his furlough to study a t the Royal College of Science. In 1900 he served in China with the forces which were sent to quell the Boxer rebellion. On his return to India, in 1901, he was appointed Probationary Assay Master, and in April, 1902, he became Deputy Assay Master a t the Bombay Mint, an appointment he held when he joined the Faraday Society a t its foundation in 1903. In 1904, jointly with Colonel Milne, he wrote a paper on the sampling of coins, of which a few copies are still available. There are also in existence several copies of a paper (probably printed in I903 or 1904) written jointly with Mr.W. G. Nicolls, Superintendent of the Coinage Department entitled “ On the Amount of Kinetic Energy transformed at the moment of impact in a Screw-Coinage Press.” Later, in 1905, he was transferred to Calcutta for a year, returning to Bombay in July, 1906. In July, 1911, he became Assay Master a t the Calcutta Mint.I t appears that in I913 he had retired, with the rank of Lieutenant- Colonel. He was then living in a flat a t Haverstock Hill, London, in which he was fitting out a laboratory with physical and chemical apparatus. On the 1st August, 1914, however, he was directed to hold himself ready for immediate return to India and he sailed on the I I t h August to take up his old post a t Calcutta.At the time of his retirement, in 1919, he was officiating as Master of the Mint a t Calcutta. The value of his services during the war was attested by the Viceroy (Lord Chelmsford) in a letter dated 13th February, 1919, as follows :- DEAR COLONEL BOURKE, " Before you leave India I should like to send you a line expressing my deep appreciation of the services you have rendered and particularly of your devotion to duty during the stressful period of the war, I realise to the full how much we owe to your unflagging efforts when our currency difficulties seemed insurmounta.ble. It was a great pleasure to me to meet you on the scene of your labours, and I shall not forget the very interesting morning which I spent a t the Calcutta Mint when we all had the benefit of appreciating your wonderful powers of exposition. I' With every good wish, " I am, Sincerely yours, " (Signed) CHELMSFORD." In the Birthday Honours List of 1919 Lieutenant-Colonel Bourke was appointed a Companion of the Most Eminent Order of the Indian Empire.On his return to England he beught the freehold house, " The Nook," at 25 London Road, Hertford, and there settled down to enjoy his well- earned rest. He fitted two rooms as laboratories, one devoted to physical (mainly optical and electrical) apparatus, and the other to chemical work. His means were such that he was able to equip these laboratories with first-class apparatus and he must have spent many happy hours in them. His note-books are not easy to read, however, as he made large use of a form of shorthand.In recent years he became interested in X-ray work and possessed himself of the necessary ap- paratus and of a number of excellent tubes. He was particularly interested in optics and seems to have devoted much thought to the uses to which he could put roof-prisms, of which many were found in his laboratory. He had many beautifully illustrated French books which he had exquisitely bound. Scientific textbooks of every kind he bought, and every room he used contained books. Another interest in his life seems to have started when he went to China. He left a number of Japanese sword guards and bronzes which had obviously been collected with care and thought, as he left also a number of books dealing with such collections. During his 14 years' stay in Hertford he made very few friends.His library was that of a collector of no mean knowledge.He seldom entertained. Nevertheless in his home he had every com- fort he desired and his servants all loved him. It has been arranged for a bronze plaque in bas relief of the Colonel, together with his sword and his insignia as C.I.E., to be retained for the Society. G. S. W. MARLOW. Dr. M. W. Travers writes as follows :- “Colonel Bourke was very kind to me in August, 1907, when I was down with malaria and he attended me. We were both then living in the Bombay Yacht Club Chambers. I should have liked to have seen more of him after the war, but he lived out of town. We only met once and that was a t the meeting of the Faraday Society for the dis- cussion of the liquefaction of gases. “ He was one of those British soldiers who find in India their m6tier in work for which they are not actually recruited and who play an important part in the administration of the Indian Empire. The story of his career shows that a t heart he was a chemist but, probably, the poor outlook in chemistry in the eighties led him to the study of medicine and in this profession he attained to the high standard re- quired for admission to the Indian Medical Service. In this Service he could doubtless have attained even higher official honours than could be reached by the path which he chose and for which a t some personal sacrifice he prepared himself.’’LIEUTENANT-COLONEL J. J. BOURKE, I.M.S., C.I.E., Founder Member of the Faraday Society. 1865 - 1933.

ISSN:0014-7672    

DOI:10.1039/TF934300X005

出版商:RSC    

年代:1934

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. PART I. FREE RADICALS OF RELATIVELY LONG LIFE. THE CHEMISTRY OF RADICALS WITH TERVALENT CARBON. BY PROFESSOR KARL ZIEGLER, Heidelberg. Received, 1 st September, 1933. The investigators of the chemical phenomena of radicals have in the last decade largely dealt with the question of why the C-C-linkage, which in most organic molecules is quite stable, shows extraordinary weakness in hexa-phenylethane.The method of investigation followed by the various investigators-G o m b e r g, S c h 1 e n k, C o n a n t, M a r v e 1, 2 i e g 1 e r and others-consisted in substituting the phenyls of hexa- phenylethane by other residues, and examining whether the new ethanes thus obtained are completely, partially or not a t all dissociated. I leave aside the numerous analogues of hexa-phenylethane with other purely aromatic substituents. They clearly demonstrate, that the dissociation tendency of the hexa-arylethanes may fluctuate within wide limits; for the development of the theory however, they are of little importance. The first strongly modified triphenylmethyl to be mentioned here is penta-phenyl-ethyl found by S c h 1 e n k and M a r k,l a wholly mono- molecular radical whose existence makes it evident that no reliance can be placed on theoretical reflections of the kind which may most simply be illustrated by placing side by side the two following formulae : /Ph -C-Ph \Ph Ph I /Ph -C-C-Ph Ph I \Ph Tetraphenyl-ally1 and pentaphenyl-cyclopentadienyl two radicals discovered by 2 i e g 1 e r and collaborators are also mono- molecular.They show that the unsaturated character of substituents is obviously ot significance for the existence of free radicals. Numerous experiments with a view to generalising this result were Ber., 55, 2285, 1922. 2 Lieb. Ann., 434, 34, I923. 3 Ibid., 445, 266, 1923. I 0K. ZIEGLER I 1 undertaken specially by M a r v e 1 who studied the properties of sub- stances with acetylenic bonds, such as, for instance: Ph Ph Ph Ph \ / \ / / \ / \ (Me)& *C =C-C-C-C =C C(Me), C = C C(Me), Ph-C-C-Ph (Me)& C =C (7.Amer. Chem. Soc., 50,2340, 1928.) [(Me)& C = C- C-C -C = C * C(Me), C =C.C(Me), (Me),C C =C (Ibid., 51, 932, 1929.) 1 1 3 [ [ I, (Ibid., "9 '737, 1928*) Me(Et),C. C =C- C-C C EC. C(Et),Me I (Ibid., 53, 3840, 1931.) These experiments were not simple. In most cases the trouble was that the substances experimented with showed a strong tendency to stabil- isation by rearrangements. In no instance was there direct proof of a perceptible dissociation into radicals. However, several hydrocarbons in solution showed sensitiveness to oxygen. All manifest a considerable weakening of the central bond by being split up, under varying conditions, by the action of an alkali metal.None of the ethanes named above, then, excels hexa-phenylethane in its tendency to dissociation. The action of acetylenic linkages in the neighbourhood of the two central carbon atoms of an substituted ethane is consequently found to be less than, for instance, that of the group - CH = C(Ph),. Ethanes with simple vinyl groups or substituted vinyl groups such as - CH = C(Me), have hitherto not been known. According to the experience with the so-called " Ally1 rearrangement " it seems safe to say that their preparation will remain impossible. The investigations just referred to were made with the object of seeking parallels between unsaturated groups and the phenyls of the hexa-phenylethane.I t could not fail to be ot interest to find out something about ethanes in which phenyls of hexa-phenylethane are substituted by saturated residues. It is well known, that hexa-methylethane is a wholly stable hydro- carbon. have shown, however, tetra- phenyl-dimethylethane and tetraphenyl-diethylethane decompose in solution spontaneously, the latter hydrocarbon more easily than the former. The radicals which first may safely be supposed to result, very quickly succumb to a dismutation in the sense of the equation : As 2 i e g 1 e r and S c h n e 11 ~ ( p h ) ~ C . CH, + (Ph), C : CH, + (Ph), CH . CH, I The action which secondary and tertiary alkyl groups show in pro- moting dissociation is very strong : tetraphenyl-dicyclohexyl-ethane (2 i e g 1 e r and S c h n e 11, Z.C.4, and diphenyl-tetracyclohexyl-ethane are, in solution, autoxidisable and give peroxides. The difference between hexa-phenylethane and its hydrogenated analogues is therefore surely not very great. 4 Lieb. Ann., 437, 227, 1924. 5 M a r v e 1, J . Am. Chem. SOC., ga, 2976, 1930.12 THE CHEMISTRY OF RADICALS Much of the same nature as these substances is ditertiary butyl- tetraphenylethane As C o n a n t has recently found 'I the dissociation tendency in ditertiary butyl-tetra-biphenyl-ethane is so marked, that solutions become distinctly coloured. The strong action of secondary alkyl residues has likewise been shown by Conant in the case of dixanthyls ; solutions of with R = cyclohexyl * isopropyl and secondary butyl show all the pro- perties of a triphenyl-methyl solution in respect of colour and reacta- bility.Dixanthyls with R = n-butyl or methyl are considerably more stable and perceptibly autoxidisable only a t higher temperature. The groups C,H, . CH2 - and (Me), CH . CH, take an intermediate position. Their action upon dissociation is not great, but decidedly greater than that of normal residues. On the whole, these investigations very clearly prove that the ten- dency to dissociation is influenced not only by the unsaturated char- acter of the ethane substituents, but also by their volume. Possibly ethane carbon atoms are, in the case of larger substituents with their need of greater space, more deplaced than the normal distance of the carbon atoms in saturated aliphatic hydrocarbons, and that this has a bearing upon the weakening of the linkage. In this sense might be interpreted the " pressure-effect " discovered by L o w e n b e i n : Solid colourless dissociable ethanes can be caused to dissociate by high pressure.The properties of pentaphenyl-ethyl now also become comprehensible ; the vohme of the triphenylmethyl residue which therein occurs as a substituent, is especially great. To summarise, it may be said that by aid of preparative organic methods two factors may be considered decisive for the dissociation: the unsaturated character of the ethane-substituents and the space they occupy. This result is largely qualitative; in none of the investi- gations referred to has an attempt been made to study the dissociation phenomena from the standpoint of exact quantitative physico-chemistry, though the radicals and their dimeres are very suitable objects for such investigations.Hitherto the term " stability of the ethane linkage " has lacked definition. This notion will have to be defined by the heat of activation required by the dissociation process. It is therefore of great importance to ascertain rates of decomposition and their temperature coefficients. A few as yet inexact experiments in this direction were made by C o n a n t with dixanthyls.1° Particularly thorough studies were undertaken by K. 2 i e g 1 e r and collaborators with hexa-phenylethane.ll The rate of dissociation of this ethane was measured by studying the 6 C o n a n t, J . Am. Chem. SOC., 50, 2041, 1928.8 J . Am. Chem. Soc., 47, 3068, 1925. lo J . Am. Chem. SOC., 51, 1925, 1929. l1 Lieb. Ann., 479, 277, 1930 ; 504, 131, 182, 1933. Ibid., 55, 2098, 1933. Ber., 66, 1855, 1927.K. ZIEGLER I 3 speed of suitable reactions. In the case of three different reagents (iodine, NO under determined conditions, and oxygen in the presence of pyrogallol) there resulted for the decomposition-constants of the hexa- phenylethane identical values, viz. 0.21 to 0.22 Min - l at OO C. in chloroform, ie., the time in which half the ethane is'dissociated under the named conditions is 3.3 Min. In all these cases, the reagent reacts instantaneously with the radical and the speed of the total reaction therefore is that of the relatively slow decomposition of the ethane.The rate of dissociation depends very little on the solvent, In about thirty media i t varies only in the ratio of I : 3. The heat of activation of hexa-phenylethane was found in various solvents to be rg Cal. & 0.5. I t seems to fall a little as the temperature rises. This figure is the first quantitative statement as to the degree of the weakening of the C-C-bond in hexa-phenylethane, for i t is known that the splitting-up of an aliphatic C-C- bond requires about 70 Cal. Considerable progress has also been made in recent years in the measurement of the equilibrium-constants. The old methods of de- termining molecular weights are very inexact. Z i e g 1 e r and E w a 1 d l 2 have developed a method of deriving equilibrium constants from measurements of molecular extinction coefficients a t varying di- lutions. By this method it was possible to calculate, for the first time, also the heat of dissociation of the hexa-phenylethane from the tem- perature coefficient of the equilibrium constants.This was found to be 10 to 12 Cal., consequently 7 to 9 Cal. smaller than the heat of activation. Half the difference, i.e., 3-5 to 4.5 Cal. is to be considered as activation energy of the radical triphenylmethyl. This amount of energy is re- quired to make a triphenylmethyl recombine with another (which also is activated) to form hexa-phenylethane. As a result of these investigations we are now intimately acquainted with all the energy changes characteristic of the system hexa-phenyl- ethane-triphenylmethyl. With the aid of tried methods it is possible to characterise in a like manner all analogous systems, and i t may be expected that exact physico-chemical research upon the phenomena of the chemistry of radicals will not be without significance for their better understanding.The exact quantitative study of radicals, however, not only affords a better understanding of known phenomena, but also leads to the discovery of new interesting phenomena. Of this two examples may be given:- ( I ) The exact kinetic study of the reaction between radicals and oxygen leads to a certain knowledge, that the familiar peroxides of the t Y Pe R-0-0-R but give two are secondary products. There are primary peroxides of the formula R . 0, or R-0-O+, hitherto overlooked, which are strongly reactive onlv last for a short time.Under suitable conditions thev can off'their oxygen to acceptors and again form radicals. processes : Th& the R- + 0 2 = R . 0 2 RO2 + A = A02 + R- .T I 12Lieb. Ann., 473, 163, 1929I4 THE CHEMISTRY OF RADICALS occasion chain-reactions, and under certain circumstances the chains become very long. In one instance, chains up to more than 50,000 links could be traced. In these experiments triarylmethyls function as very active oxidation catalysts,13 a new aspect of their chemical character, the stu*dy of which will not be without importance for the theory of autoxidation. ( 2 ) Another application of the kinetic analysis to problems of the chemistry of radicals is here mentioned but briefly: the discovery of two tautomeric forms of bis-chromenyls which are very different in point of their rates of dissociation. They were traced by Z i e g l e r and H.L u t t r i n g h a u s.14 The tautomers are to be conceived as two of the three possible molecules R-R, R-R’, R’-R’; R and R‘ being respectively. In what I have said so far I have intentionally centred on such investigations as have a secure, purely experimental basis. Of course, mention should also be made of the many labours in the field of the more theoretic treatment of the problems of the chemistry of radicals. Above all, reflections in the sphere of the theories of electrons have again and again stimulated speculation. E. H u c k e 1 l6 has recently made a comprehensive attempt to explain the existence of radicals from the standpoint of quantum me- chanics.One of the fundamentals of this theory is the assumption of a plane triphenylmethyl in which 19 electrons of methyl-carbon and the benzol-nuclei are in “ Resonanzwechsel~rkung.” As an organic chemist I do not feel competent to discuss this theory, but I see in it a stimulation to further experimental research, especially in the direction of deter- mining the dipole moment of triphenylmethyl. L 6 w e n b e i n l6 has in a simple instructive manner developed the electron formulae for some radicals with unsaturated substituents. I mention especially the formula of pentaphenyl-cyclopentadienyl Ph Ph .. c i 6’ . . . I P h : C , . . C . c *. : Ph and in which no carbon atom Pi which shows a perfect centro-symmetry distinguishes itself, as in the old formula. This formula leads to the problem of the valency-tautomerism, much discussed in recent years in connection with certain phenomena of the chemistry of radicals. 18 Z i e g I e r and E w a 1 d, Lieb.Ann., 504, 162. 1933. 14 Lieb. Ann., 504, 189, 1933. 113 Lieb. Ann., 487, 97-104, 1931. 2. Physik, 83, 632, 1933.K. ZIEGLER I 5 By way of illustration I refer to the problem of the tautomerism of the system -C--C(R), 3 -C=C(R), I I 0 II I 0 which must be discussed in the case of all radicals with carbonyl groups as substituents. Such substances as : /-\ ( L o w e n b e i n and (H. G o l d s c h m i d t ( L o w e n b e i n and S c h u s t e r , Ann., and Nagel, Ber., S c h m i d t, Ber., 481, 106, 1930.) 63, 1212, 1930. 60, 1851, 1927.) See also Ber., 61, 829, 1928.) have become known in the last few years.They are generally distin- guished by a relatively slight sensitiveness to oxygen explicable perhaps in connection with the " Enoxyl "-formulz. Again, there are the various problems of the tautomerism between diradicals and unsaturated substances, discussed by I n g o 1 d and M a r s h a l l l7 in connection with certain colour phenomena In the anthracene series, for instance : and by C 1 a r l8 in the case of the very interesting deeply coloured hydro- carbon, H It is quite impossible to mention in a short paper all the authors who have contributed to the elucidation of this problem either by discussions or by experiments.19 The great difficulties in this field which is only 1 ' J . Chem. SOC., 3080, 1926. 18 Bey., 62, 3021, 1929 ; 63,.296, I930 ; 64, 981, I931 ; 65, 503, 1932.10 See for instance H. W 1 e 1 a n d, Bey., 53, 1318, 1920 ; 55, 1806, 1922. H. G o 1 d s c h m i d t , Bey., 61, 1858, 1928. E. W e i t z, 2. Elektrochem., 34, 538, 1928. E. B e r g m a n n and E n g e l , 2. j~hysihal. Ch., Ber., 8,. 137: 1930. G. W i t t i g and W. W i e m e r, Lieb. Ann., 483, 144, 1930. G. W I t t I g and M. L e o , Ber., 64, 2395, 1931. G. W i t t i g , W. K a i r i s a n d W . H o p f , Bey., 65, 767, 1932. A. B u r a w o y, 2. physikal. Ch., Lieb. Ann., 164, I, 1933.16 THE CHEMISTRY OF RADICA LS just being gradually opened up lie in this, that the rates of conversion which occur are immeasurably great and that therefore no direct chemical methods of investigation are available. The problems of the valency tautomerism of the radicals are, however, suitable objects for spectra-photometrical investigation, possibly also for reaction-kinetics. The newly discovered autoxydative chain- reactions characteristic of radicals in the presence of acceptors deserve special attention in this connection. I should like to sum up the present situation in the field of radicals with tervalent carbon, and in that of radicals of organic chemistry in general, by saying that the field has been largely opened up by extensive preparatory work. The task to-day is not “ the making of new radicals,” but treating the available material in the spirit of exact physico-chemical methods. The requisite methods have been largely developed and need only be more generally applied. It may safely be expected that this mode of research will not exhaust itself in a quantitative description of qualitatively known results. On the contrary, it is safe to say, and a few tentative achievements go to prove it, that such methods of research will lead to the discovery of new, significant, and interesting phenomena. This summary and all the definite assertions submitted in this paper I put forward for discussion.

ISSN:0014-7672    

DOI:10.1039/TF9343000010

出版商:RSC    

年代:1934

数据来源: RSC

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118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 16 THE CHEMISTRY OF RADICA LS GENERAL DISCUSSION. Professor Lowry (Cambridge) directed attention to the interest of the formula put forward for pentaphenyl-pentadienyl, which had the same symmetrical character as J. J. Thomson’s formula for benzene, and asked for an expression of opinion as to the validity of formula of this kind containing 3-electron bonds. Dr. E. Huchl (Stuttgart) (communicated) : With respect to the re- mark of Professor Lowry I would say that by the method referred to in my paper20 I calculated some time ago the 35 electronic states (“ molecular orbitals ” in the sense of Mulliken) of the ph-electrons in the pentaphenyl-cyclo-pentadienyl-radical.21 The result gives for the ground state a charge distribution which has the symmetry of the three electron bound formula.But there are essential differences between the electronic structure of this radical and that of radicals like tri- phenylmethyl as well as of benzene. These differences cannot be expressed by a simple electronic formula. In case of pentaphenyl- pentadienyl all electronic states, occupied in the ground state, are binding states. The energy of resonance for the highest binding state is - 0.33B.This state is twofold and is occupied by three electrons. (All lower states are occupied by electron pairs.) Therefore one binding electron remains unpaired. In triphenyl-methyl, however, the highest state occupied in the ground state is not degenerated and is occupied by one electron ; we have one unpaired electron also in this case. But the highest occupied state is neither binding nor loosening. Further- more, in pentaphenyl-pentadienyl the ground state is degenerated, corresponding to two possible circulating senses of the unpaired electron : in triphenylmethyl this is not the case. The former radical should Page 40. a1 Not published.K. ZIEGLER 17 therefore have paramagnetism, due not only to the spin but due also to electronic movement, whilst the latter should have paramagnetism due to the spin only. In benzene the highest occupied electronic state is binding, not degenerated and occupied twice. There is no un- paired electron and no paramagnetism. The mean binding energy of resonance per ph-electron comes out to be : for benzene : - 4I3P for triphenylmethyl : - I'357P for pentaphenyl-pentadienyl : - 1*376j?.

ISSN:0014-7672    

DOI:10.1039/TF9343000016

出版商:RSC    

年代:1934

数据来源: RSC

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118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. K. ZIEGLER A NEW CLASS OF FREE RAD1CALS.l BY PROFESSOR A. SCHONBERG (BerZin). Received I 2th September, I 933, in German. If diphenyl disulphide (I.) or bis-(thio-a-naphthoyl) disulphide (11.) is dissolved in indifferent media, there takes place a partial rearrange- ment with formation of " free radicals " having one free sulphur bond (phenylthiyl or thionaphthoyl thiyl radicals, as the case may be) These solutions do not obey Beer's law and are thermochromatic. Solutions of diphenylene disulphide, however, obey this law ; in this case a somewhat similar formation of the radical takes place without involving, however, any change in the number of molecules. . . . . We suggest for these radicals with a free sulphur bond the name Their behaviour (under mild temperature conditions !) with noble metals, with free radicals containing tervalent carbon and with aliphatic diazo-compounds may be represented by the following formulae : Thiyl." A . S . . .* + Ag = A . S . Ag,t A . S . . . + (C6H5)3 i C . . . = A . S . C A . S . . . + (Ar), : C . . . = A . S . Na f (Ar), : C : 0,f (C6H5)3, 0 Na 2A. S + (A'),C(: N,)"" = A,' : C : (SA), + N,. 1 An abstract of a paper by A. Schonberg and E. Rupp appearing in Natur- wissenschaften, 21, 561, 1933. A = univalent residue. ** A' = univalent residue. t After experiments with Gumlich.

ISSN:0014-7672    

DOI:10.1039/TF9343000017

出版商:RSC    

年代:1934

数据来源: RSC

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118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 18 THE MAGNETISM OF FREE RADICALS THE MAGNETISM OF FREE RADICALS. BY SAMUEL SUGDEN. Received 14th August, 1933. Free radicals have been defined as substances whose molecules contain an odd number of e1ectrons.l This definition is not quite comprehensive since, for example the CH, radical found by positive ray methods is an even molecule; these exceptions are, however, rare and nearly all the free radicals which interest the organic chemist are odd molecules. Most substances whose molecules contain an even number of electrons are feebly repelled by a magnet and were described by Faraday as 1 Schlenk, 4th Cons.Chim. Solvay, 503, 1931.S. SUGDEN I9 diamagnetic. Paramagnetic substances which are attracted by a magnet include compounds of the transition elements and a few other substances. In I924 G. N. Lewis deduced that all odd molecules should be paramagnetic.2 but the quantitative discussion of magnetic phenomena presented great difficulty until the advent of the modern quantum theory. The quantum theory of magnetism has developed very rapidly in recent years and is capable of accounting for a wide range of ex- perimental data ; i t is therefore possible to predict with fair certainty the kind of magnetic behaviour which molecules of a particular type should exhibit.In terms of the modern theory the molecular mass susceptibility of a substance which is not ferromagnetic may be regarded as the sum of three terms. XM = X d + X P + x r . * (1) The first term is the diamagnetic contribution and is due to the disturbance of the electronic orbits by the applied field. I t is always negative and does not vary with temperature. In the usual units xn ranges from - 1-88 for helium to a few hundred units for a complex organic molecule. For most organic compounds xp is zero and xr is probably very small so that X d is approximately equal to xM. Some ex- amples are given in Table I. TABLE ~.-DIAMA(PNETIC AND PARAMAGNETIC SUSCEPTIBILITIES. No. Substance. He xbr XP. 0 0 0 0 1292 I303 0 0 Xr - 0 ? ? ? ? ? 44 64 If the molecule possesses a permanent magnetic moment p this gives rise to the large positive term xp which is responsible for para- magnetism.The magnetic moment is determined by the resultant angular momentum of all the electrons and this is restricted by the quantum theory to certain definite values. For a polyatomic molecule i t has been shown4 that x,+ is determined almost entirely by the nett spin S and that, to a close approximation 5 4 w + 1) T ' x,, = 1.242 x 10 In an odd molecule with one unbalanced electron S = 4 and at 20' xp = + 1270. This is much larger than xd and of opposite sign ; from ( 2 ) x,, should vary inversely as the absolute temperature (Curie's Law). Many solutions of paramagnetic ions and some solid salts obey a For a comprehensive account of this theory see van Vleck, The Theory Valence and the Structure of Atoms and Molecules, p.148. Van Vleck, ref. 3, p. 274. of Electric and Magnetic Susceptibilities. Oxford University Press, 1932.20 THE MAGNETISM OF FREE RADICALS C T - A this law over a wide range ; for others the Weiss Law, xM = - holds with considerable accuracy. x,, is usually evaluated by subtracting xd from the experimentally measured value of x ~ . Pascal has shown that in diamagnetics the susceptibility is nearly an additive function ; since the diamagnetic correction is usually small compared with xy it can be computed with suficient accuracy by adding the appropriate constants. The data for bivalent copper and silver salts in Table I. show the relative magnitudes of x,, and xa.Even molecules have nearly always zero magnetic moment so that xp is zero. The normal state of the molecule is ST: with S = I ; this gives from equation (2) xp = 3390 and the observed values range from 3310 to 3480. Recent work on sulphur vapour indicates that S, is also 3,Z and has a strong paramagneti~m.~ The last term of equation ( I ) can usually be neglected in discussing paramagnetics. It is due to " exchange " forces, or interactions between the electrons of adjacent atoms in the molecule and the quantum theory shows that it is small, positive in sign, and independent of temperature. A feeble paramagnetism which does not vary with temperature has long been known in chromates and permanganates and appears in more complex salts, e.g. the cobaltammines, when the observed susceptibility is corrected for the diamagnetism of the attached groups.Two examples of this type of feeble paramagnetism are quoted in Table I. I t is clear from these theoretical considerations that the magnetic susceptibility furnishes a good test for the existence of free radicles (odd molecules). At room temperature such molecules should give a value of x,, = xv 1 xa of the order of + 1300 units. If xp is negative, or has a small positive value, then the molecule most probably contains an even number of electrons. The available experimental data for inorganic odd molecules are collected in Table 11. The simplest odd molecule, nitric oxide gives a value of xp of the expected order of magnitude but this is really a co- incidence.Since NO is a diatomic molecule it is necessary to consider the orbital component of magnetic moment and not the spin component only as in equation (2). A complete theory has been given by van Vleck,6 which gives a very satisfactory explanation not only of the value of the susceptibility a t room temperature but also for its variation with temperature down to - 160' C. The low value found by Son6 for nitrogen peroxide is most probably erroneous. More recently Havens has measured the susceptibility of this gas over a wide range of pressures at 20' and allowing for the varying degree of dissociation computed the susceptibilities of NO, and N,O,. (The latter is known to be diamagnetic.) For NO, he finds a molecular mass susceptibility of about 1400 units in fairly good agreement with theory.ClO, measured in benzene solution by Taylor and Lewis also gives the value predicted for an odd molecule. As a contrast the hypophosphates (Nos. 12-15, Table 11.) are dia- magnetic and must therefore be derived from the acid H,P,O, and not A striking exception is furnished by oxygen. Naud6 and Christie, Physic. Rev., 37, 174, 1931 ; Shaw and Phipps, ibid., Ref. 3, p. 269. 38, 174 ; N6e1, Compt. vend., 2035, 1932.S. SUGDEN 21 TABLE II.-ODD MOLECULES, INORGANIC. NO. 9 I0 I1 I2 13 I4 15 16 Subs tame. NO NO, t. 20 I35 20 20 20 20 20 20 20 XM. I465 I53 I392 1341 - 78 - 128 - 148 - 164 I I00 xd * - I 0 - 15 - I5 - 25 - 40 - 118 - 192 - 40 - I00 XP- I475 158 (calc. 913) I407 I 366 - 38 -48 - I 0 I2 1140 from H2P03, which is an odd molecule.This result confirms the con- clusions of Arbusov and Arbusov,13 who have prepared the true ethyl ester and find that its molecular weight (obs. 250 - 260) indicates the formula Et4P20, (M = 274). Very recently Asmussen has shown that the yellow salt of the empirical formula (KSO,),NO obtained by the alkaline oxidation of hydroxylamine disulphonic acid has only a feeble paramagnetism in the solid state whilst its blue aqueous solutions give nearly the theoretical paramagnetism for an odd molecule. This is ascribed to the change (solid) (KS03),N,02 + z(KSO,),NO (solution). Taylor and Lewis lo have also examined thallium amalgum and a solution of sodium in liquid ammonia but find only a feeble para- magnetism of the order of + 20 units per gram atom of thallium or sodium.Many metals, e.g. aluminium, whose atoms contain an odd number of electrons exhibit only feeble paramagnetism in the solid state. These magnetic anomalies are probably due to the ease with which an electron is set free giving rise to “ metallic ” conduction. For a discussion of this type of magnetic behaviour see van Vleck, op. cit., P* 347- Table 111. contains the available magnetic data for odd organic molecules. The triaryl methyls are the gee radicals which havg the longest history; so far only one, No. 17, has been examined mag- netically. Taylor found a considerable paramagnetism in a 7-2 per cent. solution of this substance in benzene, but the value deduced for xp is markedly low for an odd molecule. Too much stress cannot be placed on this value for it is based on an assumed degree of dissociation which is extrapolated from observations on more dilute solutions by Gomberg,14 and may be considerably in error.The next substance (No. 18) was prepared by Kenyon and Banfield l5 by oxidising a substance of the ‘Son4 Sci. Rep. Tohztku, I I, 139, 1922 ; Bauer and Piccard, J . Physique. 8 Son& JOG. cit. 1 0 Taylor and Lewis, Proc. Nut. Acad. Sci., 1 1 , 456, 1925 ; Taylor, J . Amer. l1 Bell and Sugden, J.C.S., 48, 1933. laAsmussen, 2. an. Chem., 212, 317, 1933. 13J. p r . Chem., 130, 121, 1931. l4 Chem. Rev., I , 104, 1924. 1, 97, 1920. Havens, Physic. Rev., 41, 337, 1932. Chem. Soc., 48, 858, 1926. l5 J.C.S., 1612, 1926.22 THE MAGNETISM OF FREE RADICALS ** 20' 17" 17" 24" 24' structure I with silver oxide.One atom of hydrogen was removed quantitatively Me& . CH, . CMe P h . N . O H PhN+O Me,. C . CH, . CMe I I I I PhN:O PhN+O I I1 but the molecular weight remained practically unchanged. From these and other considerations Kenyon and Banfield assigned structure I1 to the red oxidation product which is therefore an odd molecule. In accordance with these structures the parent body (No. 4, Table I.) is diamagnetic whilst the red oxidation product is strongly paramagnetic and has a susceptibility of the right order of magnitude both in benzene solution and in the solid state. This substance is a remark- ably stable free radicle. After nearly two years' storage in contact with air it is unchanged in appearance and has the same susceptibility. A substance with a similar structure has been described by Wieland and Offenbacker,ls viz., diphenyl nitrogen oxide, Ph,N : 0, but this appears to be much more unstable.Substance 16, Table II., has ob- viously a similar structure. Finally Table 111. contains some preliminary results obtained by the writer in a study of the magnetism of the ketyls. The evidence for the existence of ketyls as free radicals is largely based on chemical reactions and varying views have been expressed as to the amount of free radical present in the coloured solutions obtained by the action of alkali metals on anhydrous solutions of ketones. The high reactivity of these solutions with oxygen, iodine, and alkyl iodides is strong evi- dence in favour of the existence of the free radical R,C-0-Na ; Schlenk XP' -- 570 I293 1109 1080 1050 TABLE III.-FREE RADICALS. ORGANIC.17 18 I g 20 No. I Subs t ancc CL Naphthyl diphenyl methyl Cl,H&N* Phenyl +-diphenylyl ketone potassium Benzophenone potassium -I Conditions. In 7 per cent. benzene soh. Solid In 20 per cent. benzene soh. In 17 per cent. dioxan soh. In 15 per cent. dioxan soh. and Weickel,20; on the other hand Bachrnanq2l have recently ob- tained 98 per cent. yields of the pinacols by pouring the coloured sol- utions into acetic acid and conclude that the essential constituent of the coloured solution is the sodium derivative of the pinacol R, . C-0 Na R, C-ONa I l8 Bey., 47, 2111, 1914. l7 Taylor, J . Amer. Chem. SOC., 48, 858, 1926. l8 Kenyon and Sugden, J.C.S., 170. 1932. lS Sugden, unpublished data.*l J . Amer. Chem. SOC., 55, 1179, 1933. aOBer., 44, 1182, 1911.S. SUGDEN 23 It is clear however that if a free radical is present it may react very differently in acid and in alkaline solutions. Physical evidence gives a much more definite answer to the problem. Schlenk and Thal,22 showed that the soluble potassium compound of phenyl p-diphenylyl ketone had a molecular weight in ether corresponding with the simple formula R,C-0-K ; hence the substance in solution is almost entirely in the form of the free radical. The new magnetic evidence leads to the same conclusion. By using dioxan as solvent high concentrations of the ketyls were obtained and their paramagnetism placed beyond doubt. In a typical experiment a 20 per cent. solution of phenyl p-diphenylyl ketone in dioxan was found to have a mass susceptibility of - 0.593. After shaking with potassium in a stream of nitrogen the susceptibility became + 0.052. The solution was poured into water and the liberated alkali titrated; this gave a concentration of 17.4 per cent. of ketyl in the clear dark-green solution. The value of xp deduced from these results is + 1080; hence a t least 85 per cent. of the product is present as the free radical. The benzophenone-potassium compound gave a similar result; with this substance part of the ketyl was in the form of a fine crystalline suspension. The method of analysis used may overestimate the amount of ketyl present and the coloured solutions probably contain very little of the pinacol. These experiments are being extended to other ketones and other solvents to test this point more completely. Birkbeck College, University of London, Fetter Lane, E.C. 4. Ber., 46, 2840, 1913.

ISSN:0014-7672    

DOI:10.1039/TF934300018b

出版商:RSC    

年代:1934

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. S. SUGDEN 23 GENERAL DISCUSSION. Dr. R. G. W. Norrish (Cambridge) said: The extension of the study of magnetic properties to free radicals and molecules of short life should yield useful data as to their valence state, even in the case of radicals with even numbers of electrons. Thus, for example, i t is of importance to the chemist and spectroscopist alike to know whether the CH, radical is primarily liberated in a singlet or triplet state.A method capable of distinguishing between the diamagnetic properties of the former and the paramagnetic properties of the latter would yield the necessary information. [An extension of the Stern-Gerlach experiment was suggested, but relative to this see Fraser, Footnote 10, p. 184.1 Dr. E. Rabinowitsch (Copenhagen) asked: How great must the concentration of paramagnetic particles in a diamagnetic medium be in order to be detectable by magnetic measurements ? May it be possible to detect for instance, the existence of free atoms or radicals of short life-time in a reacting or an illuminated system, these paramagnetic particles being present only in an amount of I per cent. or lower ? Dr. L. Farkas (Cambridge) said: I would like to say in answer to the question as to the possibility of observing the magnetism of atoms and radicals by methods other than direct observation, that the con- version of para- to ortho-hydrogen by paramagnetic substances provides24 CONCERNING THE (Cl0,)x RADICAL such a method, which has actually been used by Dr.A. Sachsse and myself in Berlin.28 The para-ortho hydrogen conversion, practically non-existent a t normal temperatures, takes place as a homogeneous bimolecular reaction either in solution or as a gas :- H2(9ara) + x z H2turtno) + x where X is any paramagnetic molecule, atom, ion, or radical. For example, a t room temperature, about every 1o12 collisions between oxygen molecules and para-hydrogen molecules results in conversion to the ortho form. The method does not readily lend itself to the quanti- tative determination of the magnetic moment of the substance to be observed, but gives a very convenient method of finding at once if i t is dia- or para-magnetic. Recently we have investigated the magnetism of B2H, and we find it is diamagnetic at room temperature. Professor Sugden (London), in reply, said : The method of measure- ment of which I have had experience is that of Guoy. With this method an approximate estimate of the magnetic moment can be made if the concentration of a free radical is of the order of 3-5 per cent. This method is only suitable for free radicals of long life; possibly a development of the molecular beam method might be developed to deal with short lived radicals. as L. Farkas, and A. Sachsse : Sitzungsber. poluss. Akad, 268, 1933 ; 2. physik. Cheunie, 23B, I, 19, 1933.

ISSN:0014-7672    

DOI:10.1039/TF9343000023

出版商:RSC    

年代:1934

数据来源: RSC