Ab initio kinetics of ethylene elimination in quinoline and azulene derivatives

This study examines the gas-phase elimination of ethylene from a series of quinoline and azulene derivatives namely, 2-ethoxyquinoline (2-EQ), 8-ethoxyquinoline (8-EQ), 2-ethoxyazulene (2-EA), and 8-ethoxyazulene (8-EA) using computational methods over the temperature range of 298-1200 K. Density functional theory (DFT) calculations were performed with the M06-2X and ωB97XD functionals and complemented by the composite G3MP2 method. Thermochemical and electronic properties, including enthalpies of formation, frontier molecular orbitals, chemical hardness, and molecular electrostatic potential, were analyzed. The reliability of the computational approach was evaluated through comparisons of calculated enthalpies of formation with available experimental and theoretical literature data, as well as by assessing correlations between G3MP2 and DFT results. Kinetic parameters for all proposed reaction pathways were determined at the G3MP2 level. The results reveal that formation of the keto tautomer of 1H-cyclohepta [b]pyrrol-8-one (P7) is the most kinetically favorable pathway, proceeding via a seven-membered-ring transition state (TS7) with an activation barrier of 35.11 kcal/mol.