First-Principles Calculations on the Kinetics and Mechanism of the Retro-Ene Reaction of Diallyl Amine in the Gas Phase

Abstract

A computational study has been carried out on the gas-phase retro-ene reaction of diallyl amine. The energies of the stationary points have also been evaluated with the B3LYP and MP2 methods on the optimized structure using the different basis sets. The kinetic activation parameters were calculated at 648 K to enable comparison with experimental data. Two probable mechanisms are suggested for the reaction. Since the radical mechanism produced a high activation energy conflicting with the experimental results, the concerted cyclic pathway of the retro-ene reaction was considered completely and comprehensively. Natural bond orbital analysis showed that the acidic character of the HI atom plays an important role in the reaction process. Wiberg bond indices were calculated throughout the reaction, and an asynchronousity value of 70% was obtained, confirming a distorted chair-like geometry for the transition state with the early and advanced natures of bond formation and bond cleavage. To provide a reasonable analysis of the critical points and the Laplacian of the electronic charge density in the TS, the atoms-in-molecule method was applied. Topological analysis showed the expected ring point for the best transition state corresponding to the cyclic six- membered structure. Comparison between the computational data and experiment showed a good agreement.