Theoretical study of the mechanisms for the homogenous gas-phase elimination kinetics of some 2-hydroxynitroalkanes

Theoretical studies for the kinetics of the gas phase elimination of 2-hydroxynitroalkanes were carried out at MP2/6-31G* level of theory. The mechanism for both secondary and tertiary 2-hidroxynitroalkanes thermolysis is retro-aldol type. In the case of the secondary 2-hydroxynitroalkanes, that is, 3-nitro-2-butanol and 3-nitro-2-pentanol, the elimination reaction proceeds via a six-membered cyclic transition state with the formation of actetaldehyde and the corresponding nitroalkane. In the case of the tertiary 2-hydroxynitroalkane, 2-methyl-3-nitro-2-propanol, the reaction also proceeds through a six-membered cyclic transition state to give acetone and nitromethane. The calculated kinetic and thermodynamic parameters are in reasonable agreement with the reported experimental values. NBO charges revealed that polarization of both N delta+-C-alpha(delta-) and C-alpha(delta-)-C-beta(delta+) bonds are important factors in the decomposition process. The tertiary substrate is favored due to stabilization of the C-beta(delta+) positive charge in the TS. The NBO analysis showed that these reactions are concerted and polar in nature. Copyright (c) 2006 John Wiley & Sons, Ltd.