Quantum Chemistry Aspects of the Solvent Effects on 3,4-Dimethyl-2,5-dihydrothiophen-1,1-dioxide Pyrolysis Reaction

A theoretical density functional theory (DFT) study was employed to investigate solvent effects on a retro-cheletropic ene reaction. The use of a nonpolar solvent in this retro-ene reaction is desirable to improve the reaction rate. Interactions between 14 different solvents and the reaction mixtures (reactant and transition state) were considered using DFT solvation calculations. These results were used to determine the role of solvents on the rate constants. Theoretical calculations at the B3LYP/6-311++G­(d,p) level revealed that in the presence of solvents with low polarity the reaction becomes faster, which is in accordance with experimental data. Transition state–solvent interactions were analyzed by the quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analysis. Finally, several correlations between electron densities in bond critical points of the C–S bond and interaction energy as well as vibrational frequencies at the transition state have been investigated