On the mechanism of intramolecular nitrogen‐atom hopping in the carbon chain of C 6 N radical: A Plausible 3c−4e crossover π ̂ Long‐Bond

Linear isomers of C 6 N radical differ in the position of the nitrogen atom in the carbon chain of C 6 N. Reaction routes, involving intramolecular nitrogen atom insertion at varying position in the carbon chain of C 6 N, are analyzed for the isomerisation between linear isomers of C 6 N. Through an automated and systematic search performed with global reaction route mapping of the potential energy surface, thermal isomerisation pathways for C 6 N radical are proposed based on the computations carried out at CASSCF/aug‐cc‐pVTZ, and CCSD(T)/6‐311++G(d,p)//B3LYP/6‐311++G(d,p) levels of the theory. Notably, a high lying linear isomer, centrosymmetric with respect to the nitrogen atom, is observed to be stabilized by a unique crossover three center‐four electron π long bond between the carbon atoms that are spatially separated by a nitrogen atom in a natural bond orbital. This long bond is concluded to be responsible for the predicted thermal isomerisation to be more feasible than the dissociation during the isomerisation pathway of a linear isomer of C 6 N. © 2014 Wiley Periodicals, Inc.