Nonempirical calculations of potential-energy surfaces for nucleophilic addition of H− and F− to an acetylene molecule

The minimal energy paths for the nucleophilic addition of a hydride ion (H^–) and a fluoride ion (F^–) to a molecule of acetylene (A) have been calculated with the use of 3–21++G and 3–21+G double basis sets in the framework of the Hartree-Fock-Roothaan method. The values of the total energies of the reactants, transition states, and products have been refined by means of calculations with more complete basis sets [6–31++G// 3–21++G and 6–31++G*//3–21++G for reaction (1); 6–31+G*//3–21+G and 6–31++G**//3–21+G for reaction (2)] and by taking into account the correlation energy for reaction (1) in the framework of the SCEP/6–31++*//3–21++G method. It has been established that the activation energy of reaction (2) is 15.94 kJ/mole lower than that for reaction (1), that reaction (1) is exothermic, and that the enthalpy change accompanying reaction (2) is close to zero. The character of the distribution of the electron density along the minimal energy paths of both reactions has been analyzed, and the differences appearing as a result of the replacement of the soft nucleophile H^– by the harder nucleophile F^– have been ascertained. The results of the calculations have been compared with the results available in the literature for reaction (1).Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 2, pp. 149–155, March–April, 1989.     

Supercritical <Emphasis Type="Italic">n</Emphasis>-butane isomerization

Supercritical n-butane isomerization over the solid acid catalysts sulfated zirconia, TiO₂-supported H₄[Si(W₃O₁₀)₄] · xH₂O (Keggin-type heteropoly acid), and H-mordenite is studied in a flow reactor. The critical parameters of n-butane are calculated for a wide range of reaction conditions. Changing from gaseous n-butane to supercritical n-butane markedly extends the lifetime of the catalysts. Under supercritical conditions, the activity and selectivity of the catalysts are invariable, provided that the density of the reaction mixture is in the vicinity of the critical density of n-butane. After the catalysts are deactivated in the gas medium, they can be partially or completely reactivated in the supercritical fluid.Translated from Kinetika i Kataliz, Vol. 45, No. 6, 2004, pp. 942–946.Original Russian Text Copyright © 2004 by Bogdan, Klimenko, Kustov, Kazanskii.     

Comparative quantum chemical investigation of structures and properties of diazocyclopropane and other diazoalkanes

The electronic structures and dissociation energies of diazocyclopropane (1), diazomethane (2), 2-diazopropane (3), and diazocyclobutane (4) were calculated at the density functional B3LYP and the ab initio MP2 levels using the 6-31G(d) basis set and at the G2(MP2,SVP)//B3LYP/6-31G(d) level. Distinctive features of diazocyclopropane 1 are the low energy of dissociation with loss of the nitrogen molecule; ΔE = 18.7 kcal mol⁻¹, B3LYP; 9.2 kcal mol⁻¹, G2 at 0 K) and a nonplanar structure, in which the C=N bond forms an angle of 115.7° with the plane of the cyclopropane ring. The behavior of molecules 1 and 2 in the 1,3-dipolar cycloaddition to ethylene (5), acrylonitrile (6), and methyl acrylate (7) was studied. The reactions of 1 with 6 and 7 have very low activation barriers (ΔE _a = 4.7 and 4.4 kcal mol⁻¹, respectively; at the B3LYP level). For these reactions, the G2 method gives even smaller activation parameters (1.8 and 0.3 kcal mol⁻¹, respectively). The results of our calculations provide a good explanation for high reactivity of diazocyclopropane 1. Dedicated to Academician N. K. Kochetkov on the occasion of his 90th birthday. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1072–1076, May, 2005.     

3-Alkyl-2-[3(4)-pyridyl]-5-(2-vinyloxyethoxymethyl)-oxazolidines

1-Alkylamino-3-(2-vinyloxyethoxy)-2-propanols react with 3-and 4-pyridinecarbaldehydes to give equimolar mixtures of cis- and trans-3-alkyl-5-(2-vinyloxyethoxymethyl)-2-[3(4)-pyridyl]oxazolidines.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 1, 2005, pp. 104–108.Original Russian Text Copyright © 2005 by Kukharev, Stankevich, Lobanova, Klimenko, Kukhareva.