THEORY OF SUBSTITUENT EFFECTS ON PERICYCLIC REACTION-RATES - ALKOXY SUBSTITUENTS IN THE CLAISEN REARRANGEMENT

Transition structures, activation energies, and reaction energies were calculated by ab initio quantum mechanical methods for the Claisen re arrangements of five hydroxy-substituted allyl vinyl ethers. The RHF, DFT-(Becke3LYP), and CASSCF methods with the 6-31G basis set were car ried out. There is good agreement with activation energies measured fo r alkoxy-substituted compounds. The activation energies were separated into thermodynamic and intrinsic effects using Marcus theory as adapt ed by Murdoch for pericyclic reactions. Intrinsic effects were analyze d by frontier molecular orbital theory. The deuterium kinetic isotope effects calculated at the CASSCF/6-31G level for the 2-OH allyl vinyl ether are in good agreement with the experimental results for the 2-O SiMe(3) derivative, arid these calculated isotope effects show much mo re bond-breaking and less bond-making than those at both the RHF/6-31G and Becke3LYP/6-31G* levels.