Nontotally symmetric trifurcation of an S N 2 reaction pathway

A new type of reaction pathway which involves a nontotally symmetric trifurcation was found and investigated for a typical S N 2‐type reaction, NC ‐  + CH 3 X → NCCH 3  + X ‐ (X = F, Cl). A nontotally symmetric valley‐ridge inflection (VRI) point was located along the C 3 v reaction path. For X = F, the minimum energy path (MEP) starting from the transition state (TS) leads to a second‐order saddle point with C 3 v symmetry, which connects three product minima of C s symmetry. For X = Cl, four product minima have been observed, of which three belong to C s symmetry and one to C 3 v symmetry. The branching path from the VRI point to the lower symmetry minima was determined by a linear interpolation technique. The branching mechanism is discussed based on the reaction path curvature and net atomic charges, and the possibility of a nonotally symmetric n‐furcation is discussed. © 2015 Wiley Periodicals, Inc.