The α-Effect Exhibited in Gas-Phase SN2@N and SN2@C Reactions

In order to explore the existence of -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 -oxy-Nus (FO-, ClO-, BrO-, HOO-, HSO-, H2NO-) in the S(N)2 reactions toward NR2Cl (R = H, Me) and RCl (R = Me, i-Pr) using the G2(+)(M) theory. An enhanced reactivity induced by the -atom is found in all examined systems. The magnitude of the -effect in the reactions of NR2Cl (R = H, Me) is generally smaller than that in the corresponding S(N)2 reaction, but their variation trend with the identity of -atom is very similar. The origin of the -effect of the S(N)2@N reactions is discussed in terms of activation strain analysis and thermodynamic analysis, indicating that the -effect in the S(N)2@N reactions largely arises from transition state stabilization, and the hyper-reactivity of these -Nus is also accompanied by an enhanced thermodynamic stability of products from the n((N)) sigma*((O-Y)) negative hyperconjugation. Meanwhile, it is found that the reactivity of oxy-Nus in the S(N)2 reactions toward NMe2Cl is lower than toward i-PrCl, which is different from previous experiments, that is, the S(N)2 reactions of NH2Cl is more facile than MeCl. (c) 2013 Wiley Periodicals, Inc.