New insight into experimental and theoretical properties of some para-like substituted 2-azidothiophenes
Abstract
The para-like substituent effect on the thermolysis of a number of 5-substituted (-Me, -SiMe3, -COMe, COCF3) 2-azidothiophenes 1a–4a is investigated experimentally and at the AM1 and RHF/6-31G* + ZPE levels of theory. Calculated structures located along the reaction coordinate from the reactant azides 1a–4a show that the extrusion of the N2 molecule is the rate determining step of the process and leads to neutral ring-opened 4-cyano-1-heterodiene products 1c–4c in a concerted manner. The activating 5-methyl substituent of 1a causes rate enhancement with respect to the 2-azidothiophene (2ATh), whereas decreasing rates are observed in the cases of the deactivating 5-COMe and 5-COCF3 groups, 3a and 4a. Theoretical results provide a reasonable description of the para-like substituent effects on the dissociation, giving electronic structural changes and the corresponding energies involved, as practical support to the experimental data.