ANALYSIS OF SUBSTITUENT EFFECTS ON THE CLAISEN REARRANGEMENT WITH AB-INITIO AND DENSITY-FUNCTIONAL THEORY

Transition structures for the Claisen rearrangements of 2- and (E)-6-s ubstituted allyl vinyl ethers with CN, CH3, and NH2 groups were locate d with the Hartree-Fock method and the 6-31G basis set. Energies were obtained using MP2 single points and B3LYP/6-31G calculations. A Mar cus theory type analysis was applied to separate the intrinsic and the rmodynamic contributions to the activation energies. The calculations predict a decrease in the activation barrier for the 2-CN, 2-NH2, and 6-NH2 derivatives, while a large increase in the activation energy is predicted for the 6-CN derivative. The 2-CN and 6-NH2 groups decrease the barrier height due to intrinsic contributions, while the rest are controlled by thermodynamic factors. To estimate solvent effects on ra tes, SCRF calculations for benzene and acetonitrile were performed.