ABSTRACT: The Diels–Alder cycloaddition between furan and ethyl acrylate in the gas phase was investigated using density functional theory in order to elucidate its reaction mechanism and regioselectivity. Calculations were performed with the B3LYP hybrid functional and the 6-311G(d,p) basis set. Transition states were located using the QST2 algorithm, allowing construction of the reaction potential energy surface. The results indicate that the cycloaddition is a spontaneous and exothermic process that proceeds through a single concerted elementary step No stable intermediates were identified along the reaction pathway, supporting a concerted mechanism. Analysis of relative energies suggests that the reaction is governed by kinetic control. Furthermore, global and local reactivity indices derived from conceptual DFT confirm the feasibility of the reaction and are consistent with the proposed mechanistic description.

Keywords – Diels–Alder reaction , Cycloaddition,  Density functional theory , Regioselectivity, Potential energy surface.