EVALUATION OF MOLECULAR MECHANICS METHODS FOR THE CALCULATION OF THE BARRIERS TO PLANARITY AND PSEUDOROTATION OF SMALL RING MOLECULES

Molecular mechanics (MM2) methods have been utilized to estimate the barriers to planarity and/or pseudorotation for 23 small ring molecules. These methods were also used to calculate the structural parameters for different conformations of each molecule. In the case of four- and pseudo-four-membered rings (five-membered rings with double bonds), MM2 predicts the structure (dihedral angle) of the equilibrium conformation with good accuracy and does reasonably well in predicting barriers to planarity. For five-membered rings with pseudorotation, molecular mechanics methods correctly identify the preferred equilibrium conformation (Cs, C2, or planar) and also do reasonably well in predicting the barriers to planarity and pseudorotation. For bicyclic systems such as the bicyclo[3.1.0]hexanes and bicyclo[3.2.0]hept-6-enes, the MM2 program was used in conjunction with experimental data to evaluate whether one or two energy minima are present. © 1990 American Chemical Society.