Nonpotential Energy (NPE) Effects in Organic Chemical Reactions: Development of a Suitable Force Field

A preliminary analysis is given of the role of NPE effects in organic chemistry. Calculation of these effects centers around a vibrational analysis program based on a suitable force field. A simple valence force field (SVFF) is chosen for the purpose, initially on the basis of a limited range of molecular types (alkanes and alkyl halides) but capable in principle of extension as required. Special weighting is given to accurate reproduction of the entropy-rich lower frequencies, and particular attention is paid to analysis of torsional force constants and torsional frequencies.