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(-)(H2O)(n = 1,2) (X = HO, CH3O, F, Cl, Br), and α-sulfur-nucleophile, HSS(-)(H2O)(n = 1,2), toward CH3Cl. 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(-)(H2O)(n = 1,2) (X = F, Cl, Br) with ClC2H4O(-)(H2O)(n = 1,2), a normal nucleophile with similar gas basicity to XO(-)(H2O)(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.

Microsolvated Ion‐Molecule SN2 Reactions with Dual Nucleophiles Induced by Solvent Molecules

“…Usually, the study [4q,5b] of α‐effect compares HOO − (H 2 O) n with HO − (H 2 O) n , where the solvent molecules are the same. Here we found, although the solvent molecules differ, the comparison between HOO − (H 2 O) n=1‐3 and HO − (HOOH)(H 2 O) n‐1 also suggests that α‐effect exists.…”

Single Solvent Molecules Induce Dual Nucleophiles in Gas-Phase Ion–Molecule Nucleophilic Substitution Reactions

“…Understanding the effect of solvents on chemical reactions is a central subject in chemistry. − Gas-phase studies of microsolvated ions provide a means to investigate the role of individual solvent molecules and may shed light on the transition between gas-phase and condensed-phase reactivity. , The ion–molecule nucleophilic substitution (S N 2) reaction is a fundamental organic reaction. − Numerous experimental and computational studies on microsolvated S N 2 reactions revealed that individual solvent molecules have multiple influences on the reaction, , including reduced reactivity, ,− altered reaction dynamics, − complex reaction mechanisms, − and the enhanced α-effect. − …”

Shapeshifting Nucleophiles HO–(NH3)n React with Methyl Chloride

“…The HOO – anion is an α-nucleophile, possessing a lone pair-bearing electron adjacent to the α-position O atom, and HO – is its corresponding normal nucleophile. When α-nucleophiles display enhanced nucleophilicity relative to normal nucleophiles of similar basicity, ,,,− the term α-effect was used to describe this deviation in reactivity relative to that expected from Brønsted-type correlations …”