A mechanistic study of the electrochemical reaction between nitrostyrene and benzaldehyde: DFT calculations on all possible routes and intermediates

A theoretical investigation of the electrochemical reaction between β-nitrostyrene and benzaldehyde was conducted at the DFT M06-2X/def2-TZVP level of theory. The reaction mechanism was dissected into five proposed routes, via 3 pathways, concluding with 4 possible products (P1 to P4). To gain a comprehensive understanding, we explored these routes both in the gas phase and in solution using three solvents: dimethylformamide, methanol, and water. In the gas phase, the overall barriers of these five routes (the energy in parentheses refers to the relative G versus reactants in kcal/mol) are in this order: A2 (− 48.22) < A1 (21.29) < C1 (21.59) < B (29.81) < C2 (77.59). The ΔG for the formation of four products (the energy in parentheses refers to the relative G versus reactants in kcal/mol) are in this order: P2 (− 233.40) < P4 (− 82.13) < P3 (− 74.18) < P1 (− 46.97). Therefore, in the extra amount of both benzaldehyde and proton, P2 is the major product, in the extra amount of benzaldehyde and minimum amount of proton, P1 is preferred, and in the small amount of benzaldehyde and proton, P4 is preferred (only via C1 route). In the solvents, despite the gas phase data, path B and product P3 are a favorable path and products. Thermodynamically, the average relative G in three solvents for P3 is − 112.09 kcal/mol, for P2 is − 112.1, for P4 is − 118.46, and for P1 is − 60.25. Kinetically, the average relative G in three solvents for the transition states of P3 is − 8.25 kcal/mol, P2 is − 42.84, P4 is 34.16 via route C1 and 29.05 via route C2, and P1 is 95.81. Therefore, in the excess concentration of proton, P2 is the most favorable product by both kinetic and thermodynamic data and in low concentration of proton, P3 is the most favorable product.