Some peculiarities of the influence of molecular structure on the activation energy of radical gas-phase decomposition of aliphatic nitro compounds

Geometric parameter; of nitro and fluoronitro derivatives of nitromethane, nitroethane, 1-nitropropane, and 1-nitrobutane (for which experimental data on kinetics of radical gas-phase decomposition are available) have been determined by the MINDO/3 method. Correlations between changes in logarithm of the activation energy and those in the lengths of C-N and C-H bonds as well as in the ionization potentials have been found. The major changes in the C-N- and C-H- bonds occur when bulky atoms and groups (NO2, CI, Br, and I) are introduced into the molecules. Nonempirical calculations of energies of dissociation of the C-N bonds in the molecules of nitromethane and its halogen derivatives have been carried out. An equation was proposed which allows one to perform a high-accuracy determination of the activation energy for radical gas-phase decomposition of nitroalkanes rising the coefficients of steric interactions in the molecules calculated by the methods of molecular mechanics.