Molecular mechanics (MM4) calculations on alkenes

Abstract

The MM4 force field has been extended to alkenes. It retains most of the formalism and computational schemes that were present in MM3. Several additional cross-terms have been added in MM4 that were not present in MM3, mainly to improve vibrational frequencies but also to improve structures and energies. About 100 molecules have been examined, many in multiple conformations. Geometries are fit for the most part to within the following ranges: 0.004 Å for bond lengths, 1° for bond angles, 4° for torsion angles, and 0.5% for moments of inertia (r2). Conformational energy differences/barriers are generally fit to within 0.5 kcal/mol unless they are very large. The vibrational frequency rms error for 7 alkenes is 25 cm−1. © 1996 by John Wiley & Sons, Inc.