CHAPTER 2. Rate Constant Calculation of Benzylperoxy Radical Isomerization

Abstract

Theoretical calculations are carried out on the benzylperoxy radical four‐centre isomerization reaction. Geometry optimizations and vibrational frequency calculations are performed using three different methods (B3LYP, MPW1K and MP2) and seven basis sets [6–31G(d,p), 6–31+G(d,p), 6–31++G(d,p), 6–311G(d,p), cc‐pVDZ, aug‐cc‐pVDZ and cc‐pVTZ]. Single‐point energy calculations are performed with the highly correlated ab initio coupled cluster method in the space of single, double and triple (perturbatively) electron excitations CCSD(T) using the 6–311G(d,p), 6–311+G(d,p), 6–311++G(d,p), 6–311+G(3df,2p) and cc‐pVTZ basis sets, and with the CASPT2/ANO‐L‐VDZP level of theory. Canonical transition state theory with a Wigner tunnelling correction is used to calculate the high‐pressure limit rate constant. The rate constants at 773 K calculated with the CASPT2/ANO‐L‐VDZP//B3LYP/cc‐pVDZ and CASPT2/ANO‐L‐VDZP//B3LYP/aug‐cc‐pVDZ levels of theory are in very good agreement with the literature. These levels of theory are then used to compute the temperature dependence of the rate constant and leds to the following three‐parameter Arrhenius expressions over the temperature range 600–2000 K: k(in s−1) = (1.34×1010) T0.79 exp((‐133.1 in kJ mol−1)/RT) and k(in s−1) = (1.85×1010) T0.78 exp((‐133.9 in kJ mol−1)/RT) at the CASPT2/ANO‐L‐VDZP//B3LYP/cc‐pVDZ and CASPT2/ANO‐L‐VDZP//B3LYP/aug‐cc‐pVDZ levels of theory, respectively. These relations can be used in thermokinetic models involving toluene and alkylbenzenes.