Electrochemical reduction of 4-(nitrophenyl)-1,2- and 4-(nitrophenyl)-1,4-dihydropyridines and the ESR spectra of the obtained free-radical particles

In the course of electrochemical generation the intermediate reaction products (free radicals of the nitro-and nitrosophenyl type, which appear on the cyclic voltammetric curves) were identified by ESR. The N-substituted derivatives are characterized by reduction of the dihydropyridine ring. The 4-nitrophenyl derivatives are characterized by the absence of intramolecular electron transfer during electrochemical reduction. In the case of the corresponding derivatives of 1,2-dihydropyridine intramolecular transfer of electrons and protons is possible under these conditions. Combined schemes of the primary and secondary chemical reactions involved in the electrochemical reduction of the investigated compounds are presented. It was established that the substances investigated with reference to the mechanism of the electrochemical transformations include the antihypertensive nifedipine (corinfar, fenigidine).Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 219–233, February, 1997.     

Features of complexing of molecular NMR relaxation probes with cellulose acetates in solutions

The method of active and inert NMR relaxation probes can be used for determining the degree of substitution of cellulose acetates. The formation of hydrogen bonds between the hydroxyl and acetate groups of cellulose acetate is more probable than between the hydroxyl groups, which results in relative large shielding of the free OH groups in the polymer in samples with high degrees of substitution.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1761–1765, August, 1989.We would like to thank N. I. Naimark for providing the samples of the cellulose acetates.     

Mechanism and products of electrochemical reduction of 4-nitrophenyl-2,6-dimethyl-3,5-dicyano-1,4-dihydropyridines in dimethylformamide

Free anion radicals of the nitrobenzene and nitrosobenzene type, which were identified by EPR spectroscopy, are formed in the electrochemical reduction of isomeric 4-(nitrophenyl)-2,6-dimethyl-3,5-dicyano-1,4-dihydropyridines on mercury and solid electrodes. Reduction of the dihydropyridine ring is observed only for N-substituted p- and m-nitrophenyl derivatives of 1,4-dihydropyridine. An intermediate with a 2-pyridonemethide structure was identified; a set of primary and secondary chemical reactions that are associated with the electrolytic reduction of the investigated compounds is presented.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1494–1505, November, 1988.     

Mass spectra of alliosterol and its dehydration product and of allosides A and B

The EI and LSIMS mass spectra of alliosterol and its dehydration product and of allosides A and B have been studied. The spectra of alliosterol show features characteristic for sterols of the cholestane series. A comparison of the B/E spectra of some fragments of the ions from alliosterol and its dehydro product has shown the unimportance of the conversion of the former into the latter under mass-spectrometric conditions.Institute of Chemistry of Plant Substances, Uzbekistan Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, Nos. 3,4, pp. 344–349, May–August, 1992.     

Heterocyclic nitro compounds

The IR and Raman spectra of a number of anions of the nitro derivatives of 1,2,4-triazole were investigated. On the basis of the position of the absorption maxima of the asymmetric and symmetric t vibrations of the nitro group, it is assumed that the nitro groups in the 3 and 5 positions of the triazole ring are coplanar, which should lead to an increase in the participation of the nitro group in the de localization of the negative charge of the anion. Shifts of the frequencies as a function of the nature of the cation (NH₄, Na, K, Cs) were not detected in the IR spectra of the crystalline salts. In addition, the IR spectra of the crystalline salts are similar (with respect to the frequencies) to the spectra of aqueous solutions of the salts, which may serve as proof of the identical structure of the anions in crystals and aqueous solutions.See [1] for communication XII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 120–123, January, 1972.     

Theoretical Study on the Isomerization Mechanism of Enol Ester from 2-Acyl-1, 3-cyclohexanediones

The present paper employed density function theory to investigate two reaction pathways for isomerization of enol ester proposed by Yang(path a) and the present authors(path a), respectively. The base catalytic effects of solvent triethylamine on these two reactions were also evaluated. It is demonstrated that path B is more preferable than path a due to low barrier height for the rate-determining step.     

Formation of high-spin complexes in reactions of oxides of the γ-Al2O3 type with radical pairs of sterically shielded semiquinones: A new procedure for the preparation of organometallic polyradicals and their ESR spectra

A new simple method was developed for the preparation of organometallic bi- and triradicals by the heterogeneous reaction of γ-Al₂O₃ or analogous oxides with free radicals generated in solution through the interaction of 3,6-di-tert-butyl-o-benzoquinone with 3,6-di-tert-butylpyrocatechol. An explanation was offered for the plus sign of the dipoledipole coupling constant observed previously in the ESR spectra recorded in a superstrong field at low temperatures. Deceased. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 2, pp. 298–302, February, 1997.     

Formation of furo- and difuro-1,4-dihydropyridines in the bromination 0f 2,6-dimethyl-3,5-dimethoxycarbonyl-4-(o-nitrophenyl)-1,4-dihydropyridine

Furo- and difuro-1,4-dihydropyridines were obtained by bromination of 2,6-dimethyl-3,5-dimethoxycarbonyl-4-(o-nitrophenyl)-1,4-dihydropyridine with mild brominating agents (pyridinium bromide perbromide, N-bromosuccinimide, and dioxane dibromide).Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1227–1232, September, 1987.