Control aromaticity in the thermal decomposition of 2,5-dihydrofuran, 2,5-dihydrothiophene and 3-pyrroline: a kinetic and thermodynamic study via DFT

Abstract

A theoretical study of the thermal decomposition kinetics of 2,5-dihydrofuran (1), 2,5-dihydrothiophene (2), and 3-pyrroline (3) has been carried out at the B3LYP/6-31++G**, B3PW91/6-31++G** and MPW1PW91/6-31++G** levels of theory. Our results show that the MPW1PW91/6-31++G** method is in good agreement with the available experimental values. The nucleus independent chemical shift (NICS) values of all reactants, TSs and products indicate that all studied structures are aromatic and the studied reactions are controlled kinetically and thermodynamically by the change of the aromaticity. Based on the optimized ground state geometries using the MPW1PW91/6-31++G** method, the natural bond orbital analysis (NBO) of donor–acceptor (bonding-antibonding) interactions revealed that by the increase of electronegativity of atom \( {\text{X }}\left( {{\text{O}},{\text{ S}},{\text{ NH}}} \right),{\text{ LP}}\left( {\text{e}} \right)_{\text{X1}} \to \sigma_{{{\text{C}}_{ 2} - {\text{H}}_{ 6} }}^{*} \) resonance energies and also, the HOMO-LUMO energy-gaps in the ground state structures increase. The results also suggest that in compounds 1–3, the hydrogen elimination are controlled by LP(e) → σ* resonance energies.