In this work, quantum chemistry and kinetics calculations have been performed on the retro-cheletropic ene reactions of N-phenyl-1-methyl-6-methylenecyclohexa- 2,4-dienylmethanimine (R1) and N-phenyl-2,2-dimethylbut- 3-en (R2). Two major possible mechanisms have been considered and rate constants have been calculated using the transition state theory. The simple Wigner, Eckart zero-curvature tunneling and small-curvature tunneling (SCT) methods were evaluated. The best agreement with experimental rate coefficients was found when SCT correction was applied. A mean deviation of a factor 3 on the rate coefficients is found for the studied reactions at the temperatures of 417 and 773 K. Calculated rate coefficients showed that the tunneling corrections played a critical role in obtaining accurate rate coefficients, especially at lower temperature (417 K). Calculated rate coefficients are in good agreement with the reported experimental data and similar compounds in the case of R1 and R2, respectively. These results support the concerted and stepwise paths for the gas phase reactions of R1 and R2, respectively. Computed kinetic parameters confirmed that R1 had greater reactivity than R2. This trend explains the effects of an extra phenyl-like system on the stability of the transition state and hence increases the R1 rate constant. Calculated rate constants especially at the M06 level are in better agreement with the experimental values than the B3LYP ones. Natural bond orbital (NBO) studies of the reactants and their transition states reveal that their electron delocalization change is an important factor in the determination of the reactivity order for these compounds. Finally, the nature of bond making and breaking during the reactions has been investigated using the concepts of electron charge density and Laplacian in atom in the molecule method.

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