DECOMPOSITION OF THE BENZYL RADICAL - QUANTUM-CHEMICAL AND EXPERIMENTAL (SHOCK-TUBE) INVESTIGATIONS OF REACTION PATHWAYS

Decomposition of the benzyl radical at a range of temperatures, simila r to 1450-1650 K, has been investigated using ab initio quantum chemic al and experimental (shock tube) techniques. Four possible decompositi on mechanisms are considered: (a) via a norbornadienyl intermediate, ( b) via a cycloheptatrienyl intermediate, (c) via direct ring opening, and (d) via a 6-methylenebicyclo[3.1.0]hex-3-en-2-yl (MBH) intermediat e. On the basis of the quantum chemical calculations, mechanisms c and d are found to be the dominant reaction channels. A theoretically der ived rate constant far the overall disappearance of benzyl is k = 10(1 6.6+/-0.3) exp(-97 +/- 3 kcal mol(-1)/RT) s(-1), in reasonable agreeme nt with that obtained in previous studies. The experiments were carrie d out by shock heating benzyl bromide to temperatures between 1050 and 1650 K, followed by analysis of the spectral components of benzyl bro mide, benzyl, and benzyl ''fragments''. The rate constants derived fro m these experiments by using a simple two-step kinetic model are in go od agreement with the theoretical values.