ON THE XNFORMATIONS OF LACTONE RINS

Abstract — The structures and relative energies of the various conformations have been determined for the simple lactones containing 1— 8 ring members by molecular nchanics (MM2) calculations. The 14—. 5—, 6—, 7—, and 8—membered rings are found as conformational mixtures of 1, 1, 2, 1 and)4 confornations, respectively, neglecting conforntions vith energies nre that 2 kcal/mol above the rast stable conformation. There is good agreement with the (fragmentary) experinntal inforntion available. The lactones constitute a commn class of compounds which are widely found in nature. Of special interest are the large—ring compounds, the ncrolides. These are for the most part complicated polyfunctional molecules. Specific conformations are known for several of the macrolides and a few other lactones from crystallography and otherwise (Ref. 1), and the conformations of the lit—membered cacrolide have been considered in some detail (Ref. 2). The general principles of the confornations of lactones are not well worked out, and indeed, the conformations of the snller nmbers of the series (containing ring members) wer