摘要:

Crystals of 4,4-dimethyl-2,2-diphenyl-1,3-dioxa-4-azonia-2-boranatacyclopentane are orthorhombic,a = 17.043(3),b = 6.289(1),c = 13.024(2) Å,Z = 4, space groupPna21. The structure was determined by direct methods, and was refined by full-matrix least-squares procedures toR = 0.071 for 1100 reflections withI ≥ 3σ(I). Bond angles in the five-membered ring, which has a distorted half-chair conformation, range from 101.5(4) for OBO to 107.1(4)° for NOB. Bond lengths are: mean B—C, 1.632(8), B—O, 1.506(7) and 1.556(8), N—O, 1.409(5), C—O, 1.378(9), C—N, 1.467–1.509(7–10), mean C—C(aromatic), 1.395(25) Å. The structure consists of discrete molecules separated by normal van der Waals distances.

ISSN:0008-4042    

DOI:10.1139/v74-369

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

An inhibition effect has been observed during the cathodic reduction of hydrogen peroxide on sodium tungsten bronzes (NaxWO3). The effect is explained as competition for available surface sites between hydrogen peroxide and protons. The competing reaction is believed to be the formation of hydrogen bronze (NaxHzWO3). The experimental current–potential relationships fit with the theoretical curves calculated under Langmuirian conditions of adsorption to a point 30–40 mV on the cathodic side of the current maximum.

ISSN:0008-4042    

DOI:10.1139/v74-370

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

Decachlorocyclopentaphosphonitrile N5P5Cl10is fluorinated by potassium fluorosulfite to give a mixture of chloride–fluorides N5P5Cl10−xFx(x = 1–9 ), no compound containing more than one PClF group. As for the comparable reactions of N3P3Cl6and N4P4Cl8, the dominance of thegeminalsubstitution pattern is attributed to the electrostatic or σ-inductive effect of the electronegative fluorine atom. The relative rates of the first two fluorination steps, in comparison with similar information for N3P3Cl6and N4P4Cl8, confirm the importance of π-inductive effects in determining the rates of the reactions.

ISSN:0008-4042    

DOI:10.1139/v74-371

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

not available

ISSN:0008-4042    

DOI:10.1139/v74-372

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

The mechanism of catalysis of aromatic bromination by pyridine was investigated by measuring the rates of bromination of mesitylene in acetic acid and in chloroform with and without added pyridinium or other substituted ammonium salts. Most salts increased both the second- and third-order rate constants for bromination, and pyridinium salts were no more effective than others. Bromide salts decreased the rate and sometimes the order of the bromination reaction by complexing bromine as tribromide. The formation constants of pyridinium tribromide and tetra-n-butylammonium tribromide in chloroform at 25.0° were found to be 2 × 102and 9 × 104 M−1respectively. It is concluded that in dilute solution pyridine catalysis of bromination is simply a salt effect which can be accounted for by the commonly accepted mechanism of bromination.

ISSN:0008-4042    

DOI:10.1139/v74-373

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

The composition and melting points of the bromine adducts of pyridinium bromide have been determined. Differential scanning calorimetry has been found to be particularly well suited to this type of phase study because it uses small, enclosed samples and responds rapidly to small heat changes. The adducts are described in terms of stoichiometric mixtures of pyridinium bromide and pyridinium tribromide, or in terms of a general formula PyHBr(Br2)nwherenequals 1/3, 1/2, 2/3, 1, 3, 6, 18. When pyridinium bromide is allowed to pick up bromine isothermally in an apparatus for thermogravimetric analysis it does so in a stepwise manner with a plateau for each of the above adducts plus one withnequal to 3/2. This provides valuable confirmation of the compositions of adducts deduced from conventional phase diagrams.

ISSN:0008-4042    

DOI:10.1139/v74-374

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

Two processes were observed by study of the variable temperature p.m.r. spectra oftrans-syn-trans-4,5:9,10-biscyclohexano-1,3,6,8-tetraoxecane (1), one of which, an equilibrium, was still rapid at −88°; the other had an energy of activation (ΔG≠) of 11.7 kcal/mol. These processes are interpreted in terms of interchange in the 10-membered ring between four conformations, namely, two degenerate pairs of diastereomeric boat–chair–boat (BCB) conformations. Possible pathways of conformational interconversion are discussed.

ISSN:0008-4042    

DOI:10.1139/v74-375

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

The reaction of chlorine monoxide with cyclohexene at −20° in the dark was found to proceed by an addition reaction to yieldtrans-2-chlorocyclohexyl hypochlorite. Concomitant with the addition, a molecule induced homolysis reaction of the chlorine monoxide occurs with cyclohexene to produce a number of free radical substitution and addition products, as well as products possibly arising from ionic addition reactions. Induced halogenation was found with added cyclohexane.

ISSN:0008-4042    

DOI:10.1139/v74-376

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

The radiolysis ofn-butane was investigated at temperatures ranging from 17 to 548 °C in both static and flow systems.It was concluded that in the radiation-sensitized thermal cracking region the main products, methane, ethane, ethylene, and propylene, were formed by a radical chain mechanism. The conclusion was reached from comparison with the thermal cracking products, the effect of ammonia addition, the dose rate dependence, and in particular the correlation between the temperature change of the type of the main chain-termination reaction and that of the activation energy of propylene formation. The value of the activation energy for propylene formation showed that the main chain-termination reaction at temperatures between 410 and 520 °C was a combination reaction of ethyl radicals. The major part of 1-butene,trans-2-butene, andcis-2-butene, formed in the chain region, was shown to result from the thermal decomposition of the chain carrying butyl radicals.Rate parameters for some of the reactions involved were calculated.

ISSN:0008-4042    

DOI:10.1139/v74-377

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

The valence force field and normal modes of vibration of α-glycylglycine have been calculated using the vibrational spectra of ten isotopic derivatives, selectively labeled with deuterium or nitrogen-15. It is shown that this force field permits the determination of the frequencies of glycylglycine-hydrochloride in the solid state, despite a structure very different from that of the zwitterion. The agreement is particularly satisfying for those modes of vibration most sensitive to molecular conformation. It is thus possible to use this type of calculation to determine the conformation of an oligopeptide.

ISSN:0008-4042    

DOI:10.1139/v74-378

出版商:NRC Research Press    

年代:1974

数据来源: NRC