ANALYSIS OF THE CONFORMATIONAL NATURE, RESOLVABILITY, AND THERMAL RACEMIZATION OF HETERO 2,3-DISPIRO CYCLOHEXANONES - THE WEIGHTING OF CARBONYL C-X STABILIZATION RELATIVE TO THE ELECTRONIC INTERACTION BETWEEN THE VICINAL ELECTRONEGATIVE SUBSTITUENTS

A series of hetero 2,3-dispiro cyclohexanones has been prepared. The c onformations of the syn and anti isomers were assessed in the solid st ate, in solution, and in the gas phase (the latter by molecular mechan ics calculations). The results are discussed in the light of steric, d ipole, and gauche interactions; steric contributions give evidence of controlling DELTAG(eq). On a different front, the syn/anti pairs were found to interconvert when heated in the presence of a catalytic amoun t of acid. Three representative examples of these chiral molecules wer e resolved and complete racemization was observed to result under the conditions of equilibration. A push-pull fragmentation of the cyclohex anone ring is proposed to account for these observations, with the tet hered oniom ion-enol pair reclosing to reconstitute the original, alth ough stereochemically scrambled, structure. The intervention of the th ionium ion intermediates is less thermodynamically favorable than that of oxonium ions, as expected.