Density functional (DFT) study of acyloxy carbene-carbene rearrangements

The rearrangement of the acyloxy carbene, XCOOC:H, to the carbene XC:OCHO, via a shift of the carbonyl oxygen from one carbon to another, has been investigated by the DFT method using the B3LYP potential. Different substituents taken for the study are X = H (S-0 and T-1), CH3, B, F and Cl. It has been found that the reaction proceeds in two steps and the intermediate is a four-centered structure, which is the formally neutral equivalent of the 6pi-electron cyclobutadienyl dianion. The activation energy for the first step is not affected very much with change in the substituent (X), but the second step is very sensitive to the nature of the substituent. This has been explained on the basis of the charge transfer effects. The thermodynamic and kinetic parameters for the reaction have also been discussed. (C) 2003 Elsevier Science B.V. All rights reserved.