STOCHASTIC SEARCHES FOR LACTONE AND CYCLOALKENE CONFORMERS

The stochastic search method coupled to MM3(92) has been used to locate as many conformers as possible for 6- to 11-membered ring lactones, trans-cycloalkenes, and cis-cycloalkenes. A comparison was carried out between the conformers of lactones and cycloalkenes of the same ring size for each force field. These comparisons were carried out by means of (1) conformational distances, defined as the rms deviation between the dihedral angles of the conformers being compared, and (2), substitution, in which a lactone was transformed into an olefin and vice versa, trying to keep as much as possible the initial geometry, followed by reoptimization. It is found that cycloalkenes and lactones share many common characteristics. The thermodynamic information provided by MM3 was used to study the dependence of conformer population upon (1) temperature and (2) total number of conformers.