摘要:

A dimer of HCN,N-cyanomethanimine6, was prepared by flash pyrolysis (gas phase, 10−2 mbar) from 3-azido-1,2,4-triazole1aand detected by ultraviolet photoelectron spectroscopy (HeI). Its ionization potentials were measured and the ionic states sequence proposed, with the aid ofabinitio– CI (configuration interaction) calculations. The study of the MNDO potential hypersurface enabled us to propose a mechanism of the thermal reorganization of the precursor1a. It is shown that the reaction path passes through the formation of the protomer1bbefore thermal decomposition and the generation of the nitrene2b.

ISSN:0008-4042    

DOI:10.1139/v88-337

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The highly hindered 8,9 double bond in lanostane derivatives was found susceptible to oxidation with ozone. The reaction depends on the polarity of the solvent. It is proposed that the structure of the initial complex formed between the olefin and ozone is influenced by the reaction medium. Reaction of 3β-acetoxy-5α-lanost-8-ene with ozone gives 8α, 9α-epoxide in methylene chloride, while 3β-acetoxy-5α-lanost-8-en-7-one, an allylic oxidation product, is the main compound formed in ethyl acetate.

ISSN:0008-4042    

DOI:10.1139/v88-338

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The equilibrium ZnS(c, sphalerite) + 2HCl(g) = ZnCl2(g) + H2S(g) was studied by modified entrainment in the temperature range 1023 to 1263 K and the free energy equation, ΔG0/J mol−1 = (95060 ± 2700) − (38.7 ± 2.4)T, was obtained. A free energy equation for the corresponding equilibrium, ZnS(c, sphalerite) + 2HCl(g) = ZnCl2(1) + H2S(g), was derived using ancillary thermodynamic data, ΔG0/J mol−1 = (−28340 ± 2800) + (85.6 ± 2.4)T, (638–978 K).

ISSN:0008-4042    

DOI:10.1139/v88-339

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

A bibliographical study of the thermal decomposition of the ethyl radical shows that the kinetic parameters for the upper and lower limits of the pressure are rather scattered. This observation explains why we have carried out a new study of this elementary process in the pyrolysis of ethane, around 800 K, in a closed vessel and at pressures of the hydrocarbon varying from 1 to 300 Torr. The experimental results have been treated according to three theoretical approaches: the RRKM theory and two methods proposed by Troe. In each case, an excellent fit of the theoretical curves with the experimental data is obtained, as well as Arrhenius expressions for the reaction rate constants at high and low pressures. A detailed critical analysis of our results as well as those found in the literature shows that as yet there is no good agreement between recent studies on this subject. However, it is possible to present two Arrhenius expressions for the reaction rate constants at high and low pressures; these expressions represent a good compromise for the results obtained by various authors:[Journal translation]

ISSN:0008-4042    

DOI:10.1139/v88-340

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

Cobalt(II) and nickel(II) thiolates, M(SR)2, can be prepared in high yield by the electrochemical oxidation of a metal anode in an acetonitrile or acetone solution of RSH (R = C6H5,o-CH3C6H4, 2-C10H7, 2,3,4,5-C6F4H; not all combinations). When 2,2-bipyridine or 1,10-phenanthroline (=L) is added to the electrolyte phase, the products are the adducts M(SR)2L2. In the case of Co(SC6H5)2(phen)2, aerial oxidation leads to the formation of the cobalt(III) cation [Co(SC6H5)2(phen)2]+, isolated as the perchlorate salt. X-ray crystallographic analysis showed that this cation has acis-CoS2(N2)2kernel.

ISSN:0008-4042    

DOI:10.1139/v88-341

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

Diphenylsilane reacts photochemically, at low temperature, on the η(tricarbonylchromium) arenes, to give unstables hydrosilylcomplexes, (η-C6R6)(CO)2Cr(H)SiHPh2with a three-center two-electron bond, Cr—H—Si; according to29Si NMR data, the degree of this bond is higher than both the degree of the Mn—H—Si bond in isoelectronic manganese compounds, (η-C5R5)L2Mn(H)SiHPh2, and the degree of the three-center Cr—H—Si bond in the permethylated complex, (η-C6Me6)(CO)2Cr(H)SiHPh2, of chromium. The variation ofdepending on the electron density of the metal is discussed.

ISSN:0008-4042    

DOI:10.1139/v88-342

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

New equilibrium figures are obtained for finite numbers of point charges confined to a sphere and interacting via a Coulomb potential. The symmetries of the configurations are classified for all cases up to a charge number of forty. Features of the geometry of the configurations are discussed and shown on equal area projections. The substantial number of configurations now available permit study of frequency of occurrence of various symmetries and persistence of certain geometries over a range of charge numbers, as well as detailed comparison of similarities and differences of the present global minimum energy figures with corresponding close packed structures.

ISSN:0008-4042    

DOI:10.1139/v88-343

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The homo and heteroassociation patterns of lupinine and epilupinine in different solvents and at various concentrations have been studied. Inn-hexane,n-heptane, CCl4, and C2H4Cl2solvents, lupinine monomers with an intramolecular OH … N hydrogen bond dominate over homoassociates with an OH … O′ intermolecular hydrogen bond even in concentrated solutions. Homoassociation of lupinine by intermolecular OH … N′ hydrogen bonding is observed only in saturated solutions. In chloroform solution any intermolecular homoassociation is effectively blocked because of significant affinity of chloroform molecules acting as a weak acid toward the free electron pairs of the oxygen atom from the hydroxyl group that would be otherwise engaged in intramolecular OH … N hydrogen bonding. Epilupinine inn-hexane,n-heptane, CCl4, C2H4Cl2, and chloroform solutions forms possible homoassociates both by OH … N′ and OH … O′ intermolecular hydrogen bonding. In dioxane-d8, DMSO, and D2O solvents both lupinine and epilupinine form heteroassociates with solvent molecules.

ISSN:0008-4042    

DOI:10.1139/v88-344

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The polarographic reduction of samarium(III) cryptates with cryptands 222, 221, and 22 was investigated in propylene carbonate. The samarium(III) cryptates are reduced in two consecutive steps, the first step was reversible and corresponded to the reduction of the Sm(III) to the Sm(II) cryptate. The Sm(III)/Sm(II) redox potential of the cryptates depended on the anion used in the complex and, in the case of the cryptate with chloride anions, a stable mixed complex was observed in propylene carbonate. The Sm(III)/Sm(II) redox potentials of the cryptates were more cathodic than the redox potential of the uncomplexed Sm(III)/Sm(II) couple, which is typical of a lower stability of the reduced cryptate. Propylene carbonate does not stabilize low oxidation states of lanthanides by cryptation. This is at variance with behavior observed previously in other media like water and methanol. Variations of redox potentials as a function of increasing amounts of water were accounted for by solvent shielding of samarium(III) upon encapsulation in cryptands.

ISSN:0008-4042    

DOI:10.1139/v88-345

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

DL-γ-Carboxyglutamic acid (Gla) reacts easily and quantitatively with aldehydes to give the racemic diastereoisomers of 5-substituted-4,4-dicarboxyprolines. After heating at 100 °C for 30 minutes these amino acids lose a carboxyl group from C-γ of Gla and C-4 of the proline ring to give glutamic acid and the racemic diastereoisomers of cyclic analogs of glutamic acid respectively. This paper reports a study of the above-mentioned compounds by using FAB mass spectrometry in comparison with CI analysis. FAB turned out to be an adequate ionization technique for dealing with such nonvolatile and thermolabile amino acids, and may thus allow the development of a rapid and sensitive method for detecting γ-carboxyglutamic acid in urine and in other biological matrices in pathological cases (i.e., renal stones and blood serum).

ISSN:0008-4042    

DOI:10.1139/v88-346

出版商:NRC Research Press    

年代:1988

数据来源: NRC