In this work, density functional theory (DFT) method was employed at the M062X/6–311G (d,p) level of theory to investigate the Diels-Alder reaction of isobenzofuran and ethylene in the gas and solution phases theoretically. To perform the computations in the solution phase, the polarizable continuum model (PCM) was applied. It was evaluated how the solvent affects the barrier height (DE‡) and thermodynamic parameters (DG‡ and DH‡) in this reaction. The dependency of these parameters on the Onsager function was discussed. The polar character of the reaction was measured through the global electron density transfer (GEDT). The Wiberg bond indices were used to assess the progress of the reactions, and the synchronicity values of the reactions were determined. Results revealed that, the barrier energy values of the reaction increased in solution phase compared to gas phase. GEDT values were lower than 0.15 e and activation barrier higher than 18 kcal/mol in the gas and solution phases. Therefore, this reaction was considered as a non-polar DA reaction.