Examples of S_N2 reactions with small or non-existent energy barriers

Abstract

The potential energy profiles of the following S_N2 reactions were obtained using the G2 quantum chemical method: H₃N + CH₃OH₂⁺→⁺H₃NCH₃ + H₂O, H₂O + CH₃FH⁺→⁺H₂OCH₃ + FH and H₃N + CH₃FH⁺→⁺H₃NCH₃ + FH. The activation energy for the first is only ΔE ° = 6.9 kJ mol^–1, while the others have no energy barrier. These findings are discussed in the light of Marcus theory.

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