On the mechanism of phenol ozonolysis

The mechanisms of liquid-phase phenol ozonation are revised. A new mechanism in which a significant role is played by free-radical reactions is suggested for this process.     

Chemiluminescent studies for the kinetics of decomposition of Di-(tert-butyl)-trioxide

Thermolysis of di-(tert-butyl)-trioxide produces IR and visible chemiluminescence (CL) which may be ascribed to emission by singlet oxygen (IR-CL) and triplet acetone (vis. CL).     

Conformational analysis of hydrogen polyoxides

The semiempirical AM I method was used for the calculation of conformational potential energy surfaces of hydrogen trioxide and tetraoxide. The most stable conformation of trioxide is itsanti-form, which is characterized by the torsion angle = 82.3°, and that of tetraoxide is theanti, anti-form with = 80.7° (H-O-O-O) and 74.1° (O-O-O-O). The structures of the stable conformers are determined by the interaction between lone clectron pairs of oxygen atoms. The dipole-dipole interaction of OH groups is weaker than that in hydrogen peroxide. The results were used for the estimation of the polyoxide increment of the Benson's additivity scheme, _f H°[O-(O)₂] = 48±6 k1 mol^–1.Translated from lzveshyn Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1356-1361, June, 1996.     

Quantum-chemical modeling of the detachment of hydrogen atoms by the sulfate radical anion

Nonempirical quantum-chemical calculations of the transition states of reactions between the sulfate radical anion and organic compounds of various classes were performed, and the activation energies of the corresponding reactions were calculated. A correlation dependence between the calculated activation energies and the strength of substrate C-H bonds was found. The polarized continuum model COSMO was used to study the influence of solvents on the kinetics of the reactions.     

Kinetics of the reaction between dimethyldioxirane and 2-methylbutane

The kinetics of the reaction between dimethyldioxirane and 2-methylbutane in acetone solutions were studied spectrophotometrically at 25 °C. The radical-chain induced decomposition of dioxirane proceeding with the participation of the carbon-centered radicals follows the first-order kinetic law. The reaction is inhibited by dioxygen. In the presence of O₂, the dimethyldioxirane consumption is due to the homolysis of the O−O bond (at a rate constant of 6.3·10⁻⁴ s⁻¹) followed by attack of the C−H bond of 2-methylbutane by the biradical formed. The rate constant of the reaction between the alkyl radical and dimethyldioxirane was estimated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1785–1788, October, 1997.     

Effect of the medium on the decomposition rate of di-t-butyl trioxide

Using the chemiluminescence method, the effect of the medium on the overall rate constant of the thermal decomposition of di-tert-butyl trioxide has been studied. In all solvents investigated the decomposition occurs in accordance with a first order rate law. The effect of solvent on the rate constant (0°C) is analyzed.     

ESR studies of radical breakdown for di-t-butyl trioxide

ESR data show thermal breakdown of the title trioxide into peroxy and alkoxy radicals ROO^. and RO^., respectively. Equilibrium constants were calculated for the formation of tetroxide ROOOOR from two peroxy radicals. Their thermodynamic parameters were determined at temperatures ranging within 193–173 K.     

Flash Photolysis of Diphenyldiazomethane in the Presence of Organic Sulfides

The flash photolysis of diphenyldiazomethane in acetonitrile, benzene, and n-decane solutions saturated with air resulted in the formation of diphenyl carbonyl oxide Ph₂COO which decayed in combination reactions. In the presence of organic sulfides, the transfer of the terminal oxygen atom of Ph₂COO to the sulfur atom was observed. The kinetics of this reaction was studied. The absolute rate constants (k ₆, dm³ mol^–1 s^–1) of the reactions of Ph₂COO with sulfides at 295 K (acetonitrile as a solvent) varied from 4.1 × 10² (Me₂S) to 8.1 × 10⁴ (Ph₂S). The solvent effect on the reaction kinetics and product composition was studied. The mechanism of the process was discussed.     

Diffusion-controlled recombination of peroxide radicals in polyatomic esters

Pulse photolysis measurements of rate constants for the decay of peroxide radicals of seven polyatomic esters show that the reaction is diffusion-controlled for esters with 2 cP. The Smoluchowsky equation is suggested to calculate 2k_t for esters with short alkyl radicals.

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. , - , 2 . 2k_t .

     

Quantum-chemical and group-additive calculations of the enthalpies of formation of hydroxylamines and oximes

The quality of calculations of the enthalpies of formation by the G2, G3, G3B3, and G3MP2B3 methods was estimated for substituted hydroxylamines and oximes. External correction of composite methods was performed to improve the accuracy of the results. The method of homodesmic reactions was used in calculations of large compounds comprising more than seven or eight nonhydrogen atoms. The enthalpies of formation of oximes and hydroxylamines were analyzed for their correspondence to the additive rule. The enthalpy increments of the thermochemical groups characteristic of the compounds under consideration were calculated, and certain trends in their variations revealed. The conclusion was drawn that the enthalpies of formation of organic derivatives of oximes and hydroxylamines of various structures could be calculated with high accuracy.