Application of SQMFF to transition states: Thermal decomposition of methylazide and ethylazide

The established Pulay's method of scaling quantum mechanically computed quadratic force fields of moderately complex molecules is used to calculate reliable vibrational frequencies of transition states in unimolecular decomposition reactions. The basic hypothesis is the transference of the scale factors computed for the molecule in its ground state to the transition state provided that the same internal coordinates are defined. The rate limiting step is the nitrogen elimination reaction in every case and reduced potential energy surfaces have been computed at AM1 and HF/4-31G levels for methylazide and ethylazide. The respective transition states have been identified and pre-exponential factors of the rate constant have been computed. (C) 1997 Elsevier Science B.V.