Computational study of the transition state of the 2,4-dimethyl-2,4-pentanediol pyrolysis reaction in gas phase by ab initio methods

Abstract

The elimination kinetics study of 2,4-dimethyl-2,4-pentanediol in gas phase at 440°C has been carried out using ab initio MP2 method with 6-31G, 6-31Gd, 6-31Gd,p, 6-31+Gd,p, 6-311Gd and 6-311Gd,p basis functions set to explore the possibility of determining a possible concerted process with a six-membered cyclic transition state TS. Vibrational frequencies analysis was realized in order to confirm the reactant, TS and products structures. The nature of these chemical species is examined in terms of geometrical parameters and of the charge density on the TQAIM analysis. IRC calculations have been performed in order to verify that localized TS structure connect with the corresponding minimum stationary points of the reactant and products. With the aim of corroborating the reaction mechanics postulated by Chuchani et al. [1] in their experimental work, we present a theoretical study in order to calculate the rate constant and the activation parameters. Results from MP2/6-311Gd,p method was found to be in better agreement with the experimental values of the A-factor Arrhenius, activation energy and, activation enthalpy. However, at these levels of theory, it was not possible to reproduce the experimental values of the rate constant and, activation entropy.