AB-INITIO MOLECULAR-ORBITAL STUDIES OF NONIDENTITY ALLYL TRANSFER-REACTIONS

Ab initio molecular orbital(MO) calculations are carried out on the no nidentity allyl transfer processes, X(-) + CH2CHCH2Y reversible arrow CH(2)CHCH(2)X + Y-, with X(-)= H, F, and Cl and Y = H, NH2, OH, F, PH2 , SH, and Cl. The Marcus equation applies well to the allyl transfer r eactions. The transition state (TS) position along the reaction coordi nate and the TS structure are strongly influenced by the thermodynamic driving force, whereas the TS looseness is originated from the intrin sic barrier. The intrinsic barrier, Delta E(0)(d)ouble dagger, loosene ss, %L(d)ouble dagger, and absolute asymmetry, % AS(d)ouble dagger are well correlated with the percentage bond elongation, %CY(d)ouble dagg er = [(d(CY)(d)ouble dagger - d(CY)(0))/d(CY)(0)] x 100 and/or %CX(d)o uble dagger. The %CY(d)ouble dagger and the bond orders indicate that a stronger nucleophile and/or a stronger nucleofuge (or a better leavi ng group) leads to an earlier TS on the reaction coordinate with a les ser degree of bond making as well as bond breaking. These are consiste nt with the Bell-Evans-Polanyi principle and the Leffler-Hammond postu late. (C) 1995 by John Wiley & Sons, Inc.