Ab initio molecular orbital studies of nonidentity allyl transfer reactions

Ab initio molecular orbital (MO) calculations are carried out on the nonidentity allyl transfer processes, X− + CH2CHCH2Y ⇌ CH2CHCH2 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 reactions. The transition state (TS) position along the reaction coordinate and the TS structure are strongly influenced by the thermodynamic driving force, whereas the TS looseness is originated from the intrinsic barrier. The intrinsic barrier, ΔE 0‡, looseness, %L‡, and absolute asymmetry, %AS‡, are well correlated with the percentage bond elongation, %CY‡ = [(d CY‡ − d CY0)/d CY0] × 100 and/or %CX‡. The %CY‡ and the bond orders indicate that a stronger nucleophile and/or a stronger nucleofuge (or a better leaving group) leads to an earlier TS on the reaction coordinate with a lesser degree of bond making as well as bond breaking. These are consistent with the Bell‐Evans‐Polanyi principle and the Leffler‐Hammond postulate. © 1995 by John Wiley & Sons, Inc.