The α‐effect exhibited in gas‐phase S N 2@N and S N 2@C reactions

In order to explore the existence of α‐effect in gas‐phase S N 2@N reactions, and to compare its similarity and difference with its counterpart in S N 2@C reactions, we have carried out a theoretical study on the reactivity of six α‐oxy‐Nus (FO − , ClO − , BrO − , HOO − , HSO − , H 2 NO − ) in the S N 2 reactions toward NR 2 Cl (R = H, Me) and RCl (R = Me, i ‐Pr) using the G2(+) M theory. An enhanced reactivity induced by the α‐atom is found in all examined systems. The magnitude of the α‐effect in the reactions of NR 2 Cl (R = H, Me) is generally smaller than that in the corresponding S N 2 reaction, but their variation trend with the identity of α‐atom is very similar. The origin of the α‐effect of the S N 2@N reactions is discussed in terms of activation strain analysis and thermodynamic analysis, indicating that the α‐effect in the S N 2@N reactions largely arises from transition state stabilization, and the “hyper‐reactivity” of these α‐Nus is also accompanied by an enhanced thermodynamic stability of products from the n (N) → σ* (O−Y) negative hyperconjugation. Meanwhile, it is found that the reactivity of oxy‐Nus in the S N 2 reactions toward NMe 2 Cl is lower than toward i ‐PrCl, which is different from previous experiments, that is, the S N 2 reactions of NH 2 Cl is more facile than MeCl. © 2013 Wiley Periodicals, Inc.