Shapeshifting Nucleophiles HO - (NH 3 ) n React with Methyl Chloride.

The microsolvated anions HO - (NH 3 ) n were found to induce new nucleophile NH 2 - (H 2 O)(NH 3 ) n -1 via intramolecular proton transfer. Hence, the ion-molecule nucleophilic substitution (S N 2) reaction between CH 3 Cl and these shapeshifting nucleophiles lead to both the HO - path and NH 2 - path, meaning that the respective attacking nucleophile is HO - or NH 2 - . The CCSD(T) level of calculation was performed to characterize the potential energy surfaces. Calculations indicate that the HO - species are lower in energy than the NH 2 - species, and the S N 2 reaction barriers are lower for the HO - path than the NH 2 - -path. Incremental solvation increases the barrier for both paths. Comparison between HO - (NH 3 ) n and HOO - (NH 3 ) n confirmed the existence of an α-effect under microsolvated conditions. Comparison between HO - (NH 3 ) n and HO - (H 2 O) n indicated that the more polarized H 2 O stabilizes the nucleophiles more than NH 3 , and thus, the hydrated systems have higher S N 2 reaction barriers. The aforementioned barrier changes can be explained by the differential stabilization of the nucleophile and HOMO levels upon solvation, thus affecting the HOMO-LUMO interaction between the nucleophile and substrate. For the same kind of nucleophilic attacking atom, O or N, the reaction barrier has a good linear correlation with the HOMO level of the nucleophiles. Hence, the HOMO level or the binding energy of microsolvated nucleophiles is a good indicator to evaluate the order of barrier heights. This work expands our understanding of the microsolvation effect on prototype S N 2 reactions beyond the water solvent.