AB-INITIO AND SEMIEMPIRICAL STUDIES ON THE TRANSITION STRUCTURE OF THE BAEYER AND VILLIGER REARRANGEMENT - THE REACTION OF ACETONE WITH PERFORMIC ACID

Ab initio and semiempirical calculations have been performed on the re action mechanism of the Baeyer-Villiger reaction of acetone and perfor mic acid. They focus, at the rate-limiting step (RLS), on the structur es, energies, Mulliken charges, and what we refer to as evolution of t he bond orders. The geometries of the Criegee intermediate, the methyl group migration transition state structure (TSs), and the product wer e found and optimized with the HF/4-21G, the HF/4-31G, and the HF/6-31 G* basis sets of double-zeta quality in the ab initio methodology. AM 1, PM3, and MNDO were used in the semiempirical calculations. The cor relation energies were also evaluated at the MP2/6-31G//HF/4-31G and M P2/6-31G* level of theory. A discussion dealing with the nature of th e transition state structure (TSs) and its determination is presented, observing that irrespective of the method of calculation, the topolog y of the TSs and the general orientation of the transition vectors are invariant. From the calculations in vacuo, by using novel methodology , we find two reactive cycles: a central one, where the oxygen bonds b reak in close synchronicity with the methyl group migration, and a sec ondary one, where a proton is transferred. This proton seems to have p rotected the carbonyl oxygen from the attack of the methyl group. Scan ning the movement of the proton, we can observe the effect that it pro duces on the atoms belonging to the reactive cycles and, interestingly , the lack of effect on those that do not belong to it. Finally, by us ing elliptic coordinates, we see that the atoms constituting both of t he reactive cycles are found on ellipsoidal surfaces where the reactiv e centers are the foci.