Abstract
MNDO and MNDOC calculations are reported for 24 thermal reactions on the potential surfaces of ethylene, formaldehyde, methanol, ketene, glyoxal, propene and formic acid. The results are compared with those from state-of-the-art ab initio calculations. Satisfactory agreement is generally found for the geometries, frequencies and zero-point vibrational energies of transition states. The ab initio activation energies are reproduced more closely by MNDOC than by MNDO, the mean absolute deviation between the MNDOC and the best ab initio values being 8.9 kcal mol−1. The comparisons clarify the accuracy which may be expected for semiempirical calculations of transition states and thereby allow a more detailed justification for applying MNDO and MNDOC to the study of organic reactions.
