L. Kh. Baumane

Electrolytic oxidation of 2,6-dimethyl-3,5-bis(ethoxycarbonyl)-1,2-dihydropyridines in acetonitrile on platinum electrodes

Free cation radicals, which subsequently undergo deprotonation to neutral radicals and disproportionation to give the starting molecules and pyridinium cations, are formed in the electrochemical oxidation of N-substituted 2,6-dimethyl-3,5-bis-(ethoxycarbonyl)-1,3-dihydropyridines on a rotating disk electrode with a ring in solution in acetonitrile. The primary cation radicals were identified by electrochemical generation in a cell placed in the resonator of an EPR spectrometer, and the hyperfine structures of the corresponding EPR spectra were studied.

Free-radical intermediates in the electrochemical reduction of ?,? derivatives of ?-(5-nitro-2-furyl)-?-cyanoethylene

It was found by cyclic voltammetry and ESR that the excitation of the molecules of α,Β derivatives of Β-(5-nitro-2-furyl)-α-cyanoethylene in the radical-anion state by one-electron electrochemical reduction promotes chemical transformation of the other reaction centers, while preserving the nitrofuran group.

Free radicals in electrochemical reduction of 3,5-dicarbethoxy-1,4-dihydropyridines with nitrophenyl groups in positions 2, 4, and 6

In the electrochemical reduction of 2,6-bis- and 2,4,6-tris(nitrophenyl) derivatives of 3,5-dicarbethoxy-1,4-dihydropyridine, in the first stage, one of the para-nitrophenyl groups in position 2 or 6 of the heterocycle is reduced. Free radicals have been obtained and identified, the primary species being ion radicals of the nitrophenyl type. The presence of the heterocycle in the molecule of the 1,4-dihydropyridine derivative stabilizes secondary free radicals of the nitrosophenyl type. In the process of electrochemical reduction, no evidence has been found of any intramolecular transfer of electrons or protons from the dihydropyridine part of the molecule to the nitrophenyl groups. Derivatives of 2,6-bis(p-nitrophenyl)-3,5-dicarbethoxy-1,4-dihydropyridine have been synthesized, and the oxidation and methylation of these derivatives have been studied.

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.

Rotational isomers of the radical-anions of 2-carbonyl-containing derivatives of 5-nitrofuran

The radical-anions of 2-carbonyl-containing derivatives of 5-nitrofuran were obtained by electrochemical generation. Their ESR spectra indicate the existence of a mixture of O,O-cis and O,O-trans rotational isomers. The parameters of the isomers were identified by INDO calculations. The more polar form (the cis isomer) is more stable in polar media.

Nitroazines. 4. Polarographic behavior of 5-nitropyrazolo[3,4-b]pyridines and the esr spectra of their electrochemically generated free radicals

Abstract1-Methyl- and 1-phenyl-substituted derivatives of 5-nitropyrazolo[3,4-b]pyridines are reduced at a dropping mercury electrode in a single one-electron wave with the formation of radical anions in interval of potentials from −0.94 to −1.06 V. Compounds unsubstituted at the N(1) nitrogen atom give an additional polarographic wave at E1/2 = −1.4 V due to the reduction of the deprotonated form (anion). The potentials and HFS constants of the ESR spectra of the corresponding electrochemically generated free radicals are given.

Mechanism of the antioxidant action of 2,6-dimethyl-3,5-dimethoxy-carbonyl-4-(2-nitrophenyl)1,4-dihydropyridine

A comparison of data on the kinetics of the accumulation of peroxides and the ESR spectra in the case of inhibition of the autooxidation of methyl oleate by 2,6-dimethyl-3,5-dimethoxycarbonyl-4-(2-nitrophenyl)1,4-dihydropyridine (I) established that the antioxidant action of the latter is exerted by the formation of a nitroxyl radical. This radical is produced analogously to the well-known scheme from 2,6-dimethyl-3,5-dimethoxycarbonyl-4-(2-nitrosophenyl)pyridine, which is generated in the reaction medium from I and methyl oleate.

Intermediates in the electrolytic reduction of 2-pyridyl-1,3-indandiones in aprotic media

The character of the products of one-electron reduction of 2-pyridinia-1,3-indandiones (of the phthalone and ylid types) in aprotic media was studied by means of EPR spectroscopy. Free radicals with semidione structures are formed; their hfs constants are presented. Radicals with pyridinium structures are formed only under the condition of the presence of a strong electron acceptor (a cyano group) in the pyridinium ring of the molecule. The formation of unstable intermediates with dimeric structures is postulated as a result of studies by means of cyclical voltammetry.

Effect of the heteroatom on the one-electron reduction of ?-nitro derivatives of five-membered heterorings

The potentials of the first polarographic half waves of the electrical reduction in dimethylformamide (DMF) of α-nitro derivatives of furan, thiophene, selenophene, and their analogs in the benzene series and the hfs constants of the EPR spectra of the electrochemically generated anion radicals of these compounds are presented. It was established that these parameters in the series of examined heterorings regularly follow the electron affinities of the heteroatoms in their s2p2pp valence state. The relative conductivity of the electronic effects of substituents is higher (1.08) in the level of the unpaired electron of the furan ring, while the conductivities in the thiophene (0.95) and selenophene (0.94) ring are lower, than in the case of the benzene ring. The conductivity through the heterorings in the molecular state is higher by a factor of 1.2 than in the level of the unpaired electron.

π-Electron structure of the nitrofuran system

Anion radicals of 2-vinylene derivatives of 5-nitrofuran were obtained by electrochemical generation. The hyperfine structure (hfs) of the ESR spectra of these anion radicals indicates delocalization of the unpaired electron over their entire π-electron system. The effect of the vinylene grouping on the distribution of the unpaired electron in the anion radicals and on the distribution of the unpaired electron in the vinylene grouping itself was examined on the basis of the hfs constants. It was found that the vinylene grouping by localizing more than 10% of the density of the unpaired electron on itself reduces, by a factor of 1.4, the effect of substituents in the 2 position of 5-nitrofuran on the distribution of the spin of the unpaired electron in the nitrofuran framework.