Intrinsic structure-reactivity relationships in gas-phase transacylation reactions: Identity exchange of substituted benzoyl chlorides with chloride ion

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-mole cule intermediates and the rate constants of the reactions have been measur ed. The energy difference between the reactants and the transition state, D elta E-diff, has been obtained through RRKM modeling of the experimental ra te constants. Quantum calculations on the structures and energetics of the complex intermediates and transition states have been conducted, and the ca lculated energetics of the surface are reasonably consistent with the exper imental results. We find that the substituent on the neutral electrophile a ffects both the complexation energy and Delta E-diff but in a different man ner; the energy difference between the complex and the transition state doe s not remain constant for the entire system. This is different from the sub stituted benzyl chloride S(N)2 system, in which the intrinsic activation en ergy remains constant for the entire series, but can be explained in terms of the structures of the complex and transition state for these reactions.