A DFT study of transition structures and reactivity in solvolyses of tert-butyl chloride, cumyl chlorides, and benzyl chlorides

DFT computations were performed on the SN1 and SN2 solvolyses of substituted cumyl chlorides and benzyl chlorides in ethanol and water, by increasing stepwise the CCl distance and by optimization. The total energy increases with the increase in the ClC distance in SN1 reactions, while free energy of activation pass through maximum. To validate the results, the calculated free energies of activation were compared with data obtained by kinetic measurements. The structural parameters of the transition states were correlated with the Hammett substituent constants and compared with the data of hydrolyses of tert‐butyl chloride and methyl chloride, which proceed with known mechanisms. Conclusions on the mechanisms of the reactions were driven from the effect of substituents on free energies of activation. Cumyl chlorides substituted with electron‐donating (e‐d) groups solvolyze with SN1 mechanism, while the reactions of substrates that bear electron‐withdrawing groups proceed with weak nucleophilic assistance of the solvent. Benzyl chlorides hydrolyze through an SN2 pathway except those derivatives that have strongly e‐d groups, where the reaction has SN1 character, but a weak nucleophilic assistance of the water should also be taken into consideration. Copyright © 2007 John Wiley & Sons, Ltd. In the studied SN1 reactions only ΔG‡ has maximum at the TS, while ΔE‡ ΔH‡, and ΔS‡ increase continuously with the increase in the CCl distance. The nucleophilic participation of the solvent decreases with the increasing electron donation and steric hindrance in SN2 reactions, and it occurs mainly in solvolyses of substrates bearing electron withdrawing groups.