Probing the reactivity of microhydrated α‐nucleophile in the anionic gas‐phase S_N2 reaction

Abstract

To probe the kinetic performance of microsolvated α‐nucleophile, the G2(+) M calculations were carried out for the gas‐phase S N 2 reactions of monohydrated and dihydrated α‐oxy‐nucleophiles XO − (H 2 O) n = 1,2 (X = HO, CH 3 O, F, Cl, Br), and α‐sulfur‐nucleophile, HSS − (H 2 O) n = 1,2 , toward CH 3 Cl. We compared the reactivities of hydrated α‐nucleophiles to those of hydrated normal nucleophiles. Our calculations show that the α‐effect of monohydrated and dihydrated α‐oxy‐nucleophiles will become weaker than those of unhydrated ones if we apply a plot of activation barrier as a function of anion basicity. Whereas the enhanced reactivity of monohydrated and dihydrated ROO − (R = H, Me) could be observed if compared them with the specific normal nucleophiles, RO − (R = H, Me). This phenomena can not be seen in the comparisons of XO − (H 2 O) n = 1,2 (X = F, Cl, Br) with ClC 2 H 4 O − (H 2 O) n = 1,2 , a normal nucleophile with similar gas basicity to XO − (H 2 O) n = 1,2 . These results have been carefully analyzed by natural bond orbital theory and activation strain model. Meanwhile, the relationships between activation barriers with reaction energies and the ionization energies of α‐nucleophile are also discussed. © 2015 Wiley Periodicals, Inc.