Nature of the transition state in gas phase SN2 identity reactions: correlation between nucleophilicity and proton affinity
Abstract
The potential energy profiles of the cationic: A + CH3A+→+ACH3 + A (A = NH3, H2O, HF), and anionic: A– + CH3A→ACH3 + A– (A– = NH2–, OH–, F–) SN2 reactions were obtained using quantum chemical methods [MP2, G2, CCSD(T)]. A linear rate–energy relationship in the form of a correlation between the critical energy, ΔE diff, and the proton affinity of A was found within subgroups of similar nucleophiles (NH3, H2O, HF; NH2–, OH–, F– ; F–, Cl–, Br–, I–). The analysis shows that the different susceptibility for each class is due to properties of the transition structures alone, and not of the reactants.