Intrinsic Structure−Reactivity Relationships in Gas-Phase Transacylation Reactions: Identity Exchange of Substituted Benzoyl Chlorides with Chloride Ion

Abstract

The identity transacylation reactions of chloride with several substituted benzoyl chlorides, Cl- + XC6H4COCl, have been investigated. For X = p-CH3, m-CH3, H, m-OCH3, m-F, and m-CF3, the complexation energies of the ion−molecule intermediates and the rate constants of the reactions have been measured. The energy difference between the reactants and the transition state, ΔEdiff, has been obtained through RRKM modeling of the experimental rate constants. Quantum calculations on the structures and energetics of the complex intermediates and transition states have been conducted, and the calculated energetics of the surface are reasonably consistent with the experimental results. We find that the substituent on the neutral electrophile affects both the complexation energy and ΔEdiff, but in a different manner; the energy difference between the complex and the transition state does not remain constant for the entire system. This is different from the substituted benzyl chloride SN2 system, in which the intrinsic activation energy remains constant for the entire series, but can be explained in terms of the structures of the complex and transition state for these reactions.