R. R. Rakhimov

Hydrogen and electron transfer in the photoreduction reaction of quinones

Abstract The primary products of the photoreduction reaction of 3,6-di t -butyl- o -quinone in single crystals of 3,6-di- t -butyl-pyrocatechol are studied by EPR spectroscopy. Ion radical and neutral radical pairs are identified distinctly. In the case of the same o -quinone in single crystals of 2-6-di t -butyl-4-methylphenol the primary product is the radical pair composed of the two hydroxyphenoxyl radicals of phenol. This indicates the possibility of transfer of two hydrogen atoms in a single elementary photochemical event.

Fast molecular dynamics: Novel effects studied by 3 cm and 2 mm band EPR

1: Abstract - Motional characteristics were calculated for new type or free radicals starting from the anisotropic parameters obtained with the high resolution 2 mm band EPR. The general approach for derivinp; parameters of molecular tumbling and chemical exchange in the same experiment is discussed. A rather strong correlation between molecular and chemical dynamics of free radicals has been observed.

Molecular and chemical dynamics of a biradical with six-coordinate silicon atom

The intramolecular dynamics of a silicon biradical complex witho-semiquinone ligands was studied in a frozen toluene solution. Analysis of the broadening and shifts of the canonical components in the ESR spectrum of this biradical allows one to detect the abrupt reorientation of the magnetic axes due to intramolecular single bond-unpaired electron exchange. The frequencies of chemical exchange at low temperatures were estimated.

EPR Spectra of complexes of 3,5-di-tert-butyl-o-benzoquinone with lead diethyldithiocarbamate, ethylxanthate, and o,o-diethyldithiophosphate and reaction with bases

We have observed the solvent dependence of the hyperfine coupling constant for hyperfine coupling with the metal nucleus in ortho-semiquinone complexes of lead(II) diethyldithiocarbamate, ethylxanthate, and O,O-diethyldithiophosphate. This is connected with the process of solvation of the metal cation with the solvent molecules. We observe a correlation between the hyperfine coupling constant (due to the207Pb isotope) and the basicity factor of the solvent. Using the EPR method, we have studied the dynamics of solvation of the 3,5-di-tert-butyl-o-semiquinone complex of lead diethyldithiocarbamate by amines. We have obtained the thermodynamic and kinetic parameters of the solvation process. We observe a compensation effect for the kinetics of the forward and backward solvation reactions.

Correlation between the rotational mobility and the kinetics of the intramolecular exchange of the unpaired electron and bond in a tin-containing free radical with two pyrocatechol ligands

EPR spectroscopy was used to study the effect of the mobility of the medium on the dynamics of the interligand exchange of the unpaired electron and bond in the free radical formed upon the reaction of stannous bis-3,6-di-tert-butyl-o-semiquinolate with 3,6-di-tert-butyl-2-hydroxyphenoxyl in the presence of triphenylphosphine. A dependence exists between the characteristic exchange time τex and the correlation time for the rotational mobility of the radicalτc;τex=ατc. A temperature dependence was found for coefficient α.

Reaction of stannous bis-3,6-di-tert-butyl-o-semiquinolate with phenoxyl radicals

An EPR study was carried out on the reaction of stannous bis-3,6-di-tert-butyl-o-semiquinolate with several phenoxyl radicals. An oxidative addition reaction may proceed with the formation of radicals with stannic ions. The reaction of biradical stannous complexes with 3,6-di-tert-butyl-2-hydroxyphenoxyl in the presence of triphenylphosphine in toluene gave a tin-containing free radical. The EPR spectra of this radical indicated rapid interligand exchange of the unpaired electron and bond.

Correlation between solvent-reorganization dynamics and the kinetics of metallotropy in polar media

The kinetics of metallotropy of the 3,6-di-tert-butyl-2-(triphenylstannyl)oxyphenoxyl radical has been studied by ESR. The correlation between chemical exchange time τex, solvent polarity, and longitudinal relaxation time of the solvent corresponds to the model of a process controlled by molecular dynamics. A linear relation between τex and correlation time τc for reorientation movements of the radical is found: τex = α · τc. The coefficient α depends on the dielectric properties of the solvent.

Leveling of reactivity for intramolecular radical substitution reactions in viscous media

A leveling of the reactivity was found for intramolecular radical reactions in substituted 2-oxyphenoxyls in viscous media. A comparison of rate constants in toluene, hexane, pentane, and vaseline oil shows that fast reactions are decelerated more rapidly than slow reactions.

Influence of the mobility of the medium on the dynamics of metallotropy in tin-containing 2-(R-oxy)phenoxyls 3. Dynamics of nondegenerate tautomerism in viscous media

The influence of the mobility of the medium on the dynamics of the stannotropy of 3,5-di-tert-butyl-6-chloro-2-(chlorodimethylstannyloxy)phenoxyl, which is a nondegenerate tautomeric transformation, has been investigated. It has been shown that the rate of the forward and reverse reactions involving the intramolecular migration of the SnClMe2 group in the radical decreases as the mobility of the medium is lowered, but the equilibrium constant does not vary in the range of accuracy of the measurements.

Dynamics of the solvation of thallium 3,5-di-tert-butyl-o-semiquinolate by pyridine and triethylamine

The kinetic parameters were determined for forward and reverse solvation upon the interaction of thallium 3,5-di-tert-butyl-o-semiquinolate with pyridine and triethylamine. The solvation proceeds at almost the diffusion-controlled rate (k ∼ 108–109 liters/(mole·sec).