Semiempirical method of calculations of transition-state geometries for radical addition reactions

Transition-state geometries of the addition reactions of H^·, ^·CH₃, ^·NH₂, and ^·OCH₃ radicals to ethylene; H^· radical to acetylene, methyleneimine, acetonitrile, and formaldehyde; and ^·CH₃ radical to acetone and acetylene were determined by the density functional (B3LYP) method. The interatomic distances in the transition states of these reactions were also calculated from experimental data (enthalpies and activation energies) using the model of intersecting parabolas, the model of reduced intersecting parabolas (RIP), and the model of reduced intersecting parabola and Morse curve. The results obtained by different methods were compared and analyzed. An algorithm was elaborated for calculations of interatomic distances using experimental data, based on introduction of corrections to the RIP model. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 886–893, April, 2005.