Comparison of temperature effect on electroreduction of tert-butyl chloride and tert-butyl bromide—Theoretical study

Abstract

An effect of temperature on kinetics and mechanism of the reaction RX+e→R+X− is studied using molecular dynamics simulations method for two molecules: t-BuCl and t-BuBr in two different solvent viscosities γx=2ps−1 and γx=40ps−1. The potential surfaces used in the simulations are two-dimensional and depend on the solvent generalized coordinate x and the C–X bond elongation y, the latter part based on quantum calculations. For both systems the transfer coefficient α is found to decrease with temperature and this effect is stronger in the more viscous solvent. For γx=40ps−1 the following α values are reported: at T=278K 0.234 (t-BuCl) and 0.264 (t-BuBr), while at T=398K 0.208 (t-BuCl) and 0.222 (t-BuBr). In identical conditions and for the same height of the energy barrier, α(t-BuCl) is always lower than α(t-BuBr). The results are interpreted as an effect of the saddle point avoidance phenomenon.