Dynamics of nucleophilic substitution on ambident nucleophiles CN− and iodomethane: insights into the competition mechanism with neutral isomeric products

Abstract

Bimolecular nucleophilic substitution (S_N2) plays a vital role in organic synthesis. Compared with nucleophiles with one reactive center, ambident nucleophiles can form isomer products. Determining the isomer branching ratios through experiments is difficult, and research on related dynamics characteristics is limited. This study uses dynamics trajectory simulations to explore the dynamics characteristics of the S_N2 reaction of ambident nucleophiles CN⁻ and CH₃I. The calculated rate constants reproduce the experimental results at room temperature. The dynamics simulations reveal the mechanism of the competition between isomer products CH₃CN and CH₃NC with a ratio of 0.93 : 0.07. This mechanism is attributed to the height of the central barrier, which strongly stabilizes the transition state of the CH₃CN product channel of the formed C–C bond. The product internal energy partitionings and the velocity scattering angle distributions are calculated based on the trajectory simulations, and are in almost agreement with the experimental results obtained at a low collision energy. The dynamics of the title reaction with the ambident nucleophile CN⁻ are also compared with the S_N2 dynamics of one reactive center F⁻ and the substrate CH₃Y (Y = Cl, I) reactions. This intensive review shows the competition of isomer products for the S_N2 reaction of the ambident nucleophile CN⁻ in the current study. This work provides unique insights into reaction selectivity for organic synthesis.