S. L. Khursan

Structure, thermochemistry, and conformational analysis of peroxides ROOR and hydroperoxides ROOH (R = Me, But, CF3)

The equilibrium structures, total energies, and harmonic frequencies of peroxides ROOR and ROOH (R = Me, But, CF3) were calculated using the perturbation theory (MP4//MP2 method) and density functional approach (B3LYP) in the 6-31G(d,p) basis set. The conformational flexibility of peroxides under rotation about the O-O bond was investigated. It was found that the stable conformation of a peroxide molecule is determined by superposition of the destabilizing effects (repulsion between the lone electron pairs, steric hindrances) and the interaction of the nonbonding orbitals of oxygen atoms with the antibonding orbitals of the adjacent polar bonds. The latter effect stabilizes the nonplanar structure of the peroxide molecule. The role of orbital interactions in manifestation of the d-effect (distortion of the tetrahedral configuration of the X3CO fragment of peroxide molecule) was revealed. The vibrational spectra of peroxides were calculated and compared with the experimental data. The potential energy distribution over normal vibrations was analyzed. The enthalpies of formation and the bond strengths in the molecules of compounds examined were calculated in the framework of the isodesmic reaction approach.

Free-radical chain decomposition of ozone initiated by di(tert-butyl) trioxide

Di(tert-butyl) trioxide in a solution of CFCl3 (Freon-11) at –23 °C exists in equilibrium with the tert-butoxyl and tert-butylperoxyl radicals virtually without irreversible decomposition. The above radicals decompose ozone to dioxygen with a high effective rate constant, which is proprotional to the square root of the ButOOOBut concentration. The kinetic scheme describing the found relationships was proposed.

Quantum-chemical calculations of the dissociation energy of the C-H bond in hydrocarbons, alcohols, and ethers

The dissociation energy of the C-H bonds in hydrocarbons, alcohols, and ethers were calculated by semiempirical MNDO, AM1, and PM3 methods. The average error of calculations of theD(C-H) values by using various quantum-chemical methods is 1.3 kcal mol−1.

Kinetics, mechanism, and products of the reaction of diphenylcarbonyl oxide with carboxylic acids

The kinetics of the reactions of acetic, benzoic, formic, oxalic, malic, tartaric, trifluoroacetic, and hydrochloric acids with diphenylcarbonyl oxide Ph2COO was studied. The carbonyl oxide Ph2COO was generated by flash photolysis of diphenyldiazomethane Ph2CN2 in solutions of acetonitrile and benzene at 295 K. The apparent rate constants of the reaction range from 4.6·108 for (COOH)2 in MeCN to 7.5·109 L mol–1 s–1 for acetic acid in a benzene solution. The reaction mechanism was proposed, according to which at the first stage the carbonyl oxide is reversibly solvated by the solvent. Then the solvated carbonyl oxide reacts with the acid molecule by the mechanism of insertion at the O—H bond.

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 (k6, 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.

Solvent effects on the absorption spectrum and recombination kinetics of diphenylcarbonyl oxide

The absorption spectra and rate constants of diphenylcarbonyl oxide recombination in a series of solvents and their binary mixtures were determined by flash photolysis. An increase in the solvent polarity causes hypsochromic shift of the maximum in the absorption spectrum of Ph2COO. The analysis of the solvent effect on the recombination rate constant in terms of the four-parameter Koppel—Palm equation shows that the reactivity of carbonyl oxide depends on both specific and non-specific solvations. Quantum chemical B3LYP/6-31G(d) calculations of H2COO and PhHCOO carbonyl oxides as well as the complexes of H2COO with acetonitrile and ethylene in different media were performed using a polarized continuum model.