Thermolysis of 2-methyloxetane: a computational study

Abstract

Thermal fragmentation of 2-methyloxetane (2MO), which yields two different sets of products by virtue of ring asymmetry, was studied theoretically by using DFT, MPn and CASPT2//CASSCF methods. At the MPn and DFT theoretical levels, only concerted transition states were located on the ground state potential energy surface (PES). The CASSCF approach leads to different stepwise pathways for the two fragmentation modes, with biradical as intermediates, in addition to the concerted paths, with a very shallow PES for the asynchronous region in which intermediates becomes unstable under CASPT2//CASSCF calculations. Nevertheless, activation barriers thus calculated were quite consistent with experimental values. The reaction pathway that experimentally renders the main set of products was calculated as the lowest-energy path for the fragmentation of the 2-methyloxetane heterocycle, and this evolves with an initial cleavage of the C–O bond of the oxetane ring.