Unusual reaction paths of SN2 nucleophile substitution reactions CH4 + H− → CH4 + H− and CH4 + F− → CH3F + H−: Quantum chemical calculations

•High level quantum chemical calculations are performed for two SN2 reactions.•The calculated gradient reaction pathways for reactions have an unusual behavior.•An unusual saddle point of index two lies on the gradient reaction path.•VRI points have been detected by using Newton trajectories for the reaction path.•An infinite flow of gradient lines emanates at three equivalent product minima.

Quantum chemical (CCSD(full)/6-311++G(3df,3pd), CCSD(T)(full)/6-311++G(3df,3pd)) and density function theory (B3LYP/6-311++G(3df,3pd)) calculations were performed for the SN2 nucleophile substitution reactions CH4 + H− → CH4 + H− and CH4 + F− → CH3F + H−. The calculated gradient reaction pathways for both reactions have an unusual behavior. An unusual stationary point of index 2 lies on the gradient reaction path. Using Newton trajectories for the reaction path, we can detect VRI point at which the reaction path branches.

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