Effect of H/D isotope substitution on polarizability of methanol molecules

The electron polarizabilities (α₀·10²⁴/cm³ molec.⁻¹) were estimated from the data on refractive indices and molar volumes of H/D isotopomers of methanol at 25 °C using the Lorentz-Lorentz formula: 3.265 (CH₃OH), 3.260 (CH₃OD), 3.235 (CD₃OH), and 3.231 (CD₃OD). A relationship between the isotope effects for α₀ and volume (packing) changes in the structure of liquid methanol induced by deuterosubstitution in the methanol molecule was proposed. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1927–1928, August, 2005.     

Nonequilibrium nuclear polarization in the photolysis of aniline solutions

Conclusions Negative polarization of the protons of aniline and other compounds is observed upon the photoexcitation of aniline solutions. This effect is a consequence of optical nuclear polarization in short-lived donor-acceptor complexes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1890–1892, August, 1987.     

Radical pair substitution in chemically induced dynamic nuclear polarization. Co-operative effects

The problem of radical pair substitution in Chemically Induced Dynamic Nuclear Polarization is reconsidered. The singlet—triplet evolution in the radical pairs is described in a continuous fashion, assuming non-disturbance of the electron spin state during the scavenging reaction. The CIDNP effect of the recombination product of the secondary pair is demonstrated to result from the “co-operative effect” of singlet—triplet evolution in both the primary and the secondary pair. The hypothetical one proton case, in which the primary pair has different g-factors and a zero hyperfine interaction, and the secondary pair equal g-factors and a non-zero hyperfine interaction is treated qualitatively. Some examples are discussed in which older models lead to a faulty interpretation of experimental results.     

Magnetic isotope effect in the photolysis of organotin compounds

Photolysis of organotin molecules RSnMe3 is shown to be a spin selective radical reaction accompanied by fractionation of magnetic, (117,119)Sn, and nonmagnetic, (118,120)Sn, isotopes between starting reagents and products. A primary photolysis process is a homolytic cleavage of the C-Sn bond and generation of a triplet radical pair as a spin-selective nanoreactor. Nuclear spin dependent triplet-singlet conversion of the pair results in the tin isotope fractionation. Experimentally detected isotope distribution unambiguously demonstrates that the classical, mass-dependent isotope effect is negligible in comparison with magnetic, spin-dependent isotope effect.     

Mechanism of the photolysis of substituted tetraphenylporphin with p-benzoquinones in vitro according to chemical nuclear polarization (CNP) data

It is established by means of chemical nuclear polarization that the photointeraction of quinones with porphyrin leads to the transfer of an electron with the formation of ion-radical pairs, and then to the transfer of a proton with the reversible reduction of quinone.     

Chemically induced dynamic nuclear polarization in the photolysis of tetrafluoro-1,4-benzoquinone with plane polarized light evidence of phototriplet mechanism

CIDNP in the photolysis of tetrafluoro-1,4-benzoquinone was studied by using plane polarized light for excitation. Experiments show that the magnitude of CIDNP depends upon the polarization of the excitation light and thus provides evidence for the phototriplet mechanism in the initial electron spin polarization which subsequently leads to nuclear polarization by cross relaxation.     

A kinetic analysis of the photolysis of mixtures of acetone and propylene

The photolysis of mixtures of acetone and propylene at 308 nm has been studied kinetically from approximately 300 K to 580 K. Rate constants were calculated for the reactions at total pressures ranging from 110 torr to 750 torr and for [C₃H₆]/[(CH₃)₂CO] ratios in the range 0.03 to 3.3. No dependence of the rate constants on total pressure or on this concentration ratio could be detected within this range of conditions. The temperature dependence of the rate constants is given by © 1994 John Wiley & Sons, Inc.     

An ESR study of the photolysis of methanol adsorbed on silica gel

ESR has been used to study the photolysis of adsorbed methanol on various specimens of silica gel by light of wavelength 365 nm, which is found to detach -hydrogen from the OCH₃ group of the surface to give the radical SiOCH₂, which is stabilized in the pores. The alcohols CD₃OH and CH₃OD are also examined.     

Studies on the temperature dependence of isotope effects arising in low-temperature acetaldehyde photolysis

The temperature dependence of hydrogen isotope effects arising in the photolysis of mixtures of acetaldehyde-h₄ and -d₄ has been studied experimentally. The temperature maximum of these effects (ξ = 40 at T 27 K) has been found. Good agreement of theory and experiment has been obtained in the approximation of strong exciton-phonon coupling.     

Thermodynamic properties of the azeotropic mixture of acetone and methanol

The molar heat capacities of the pure samples of acetone and methanol, and the azeotropic mixture composed of acetone and methanol were measured with an adiabatic calorimeter in the temperature range 78–320 K. The solid–solid and solid–liquid phase transitions of the pure samples and the mixture were determined based on the curve of the heat capacity with respect to temperature. The phase transitions took place at 126.16±0.68 and 178.96±1.47 K for the sample of acetone, 157.79±0.95 and 175.93±0.95 K for methanol, which were corresponding to the solid–solid and the solid–liquid phase transitions of the acetone and the methanol, respectively. And the phase transitions occurred at 126.58±0.24, 157.16±0.42, 175.50±0.46 and 179.74±0.89 K corresponding to the solid–solid and the solid–liquid phase transitions of the acetone and the methanol in the mixture, respectively. The thermodynamic functions and the excess thermodynamic functions of the mixture relative to standard temperature 298.15 K were derived based on the relationships of the thermodynamic functions and the function of the measured heat capacity with respect to temperature.     

Effect of unsymmetrical substitution on the nuclear quadrupole resonance spectra of trivalent antimony

Conclusions Very strong asymmetrization of the electron distribution on the central atom occurs for the unsymmetrically substituted compounds of trivalent antimony, which is expressed in a noticeable increase of the asymmetry parameter and the constants of the quadrupole bond for¹²¹Sb and¹²³Sb when compared with compounds of the SbX₃ type.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1183–1184, May, 1972.     

Effect of the nature of inert solvent on the decay kinetics of the carbocation generated in the photolysis of 1,2-dihydroquinolines in methanol

The dependence of the quantum yield and the decay rate constant for the carbocation generated in the photolysis of 6-ethoxy-1,2,2,4-tetramethyl-1,2-dihydroquinoline (6-EtO-DHQ) in methanol on the solvent composition was studied in the mixtures of methanol with isopropanol, acetonitrile, and pentane by pulse photolysis. The addition of these solvents decreases the yield of the carbocation and differently affects the kinetic parameters of its decay. The carbocation decay in the mixtures MeOH-i-PrOH and MeOH-C₅H₁₂ is described by the pseudo-first order equation (k ₁), with the dependence of k ₁ having a maximum at 50 vol % of MeOH in the MeOH-i-PrOH mixtures, and k ₁ increasing with a decrease in the MeOH concentration in the MeOH-C₅H₁₂ mixtures. In the MeOH-MeCN mixtures, the value of k ₁ decreases with a decrease in the MeOH concentration, and, at the concentration of MeOH lower than 50 vol %, the contribution of the second-order reaction (k ₂) is observed. The activation energies and preexponential factors were determined in the MeOH-C₅H₁₂ mixtures of different compositions, and it was shown that E _act practically did not depend on the solvent composition and were close to E _act for other carbocations obtained in MeOH. The increase in k ₁ with a decrease in the MeOH concentration is caused by an increase in the preexponential factor. The results were discussed on the basis of the reaction mechanism involving the competing reactions of the carbocation combination with two nucleophilic particles, the MeOH molecule and the MeO⁻ anion. The composition of the mixture and the nature of the inert solvent affect strongly the course of these reactions. Published in Russian in Kinetika i Kataliz, 2009, Vol. 50, No. 3, pp. 411–416. The article was translated by the authors.