Quantum chemical aspects of solvent effects on the Diels-Alder reaction of 2,3-dimethyl-1,3-butadiene and diethyl azodicarboxylate

A comprehensive theoretical study was performed regarding the solvent effect on the Diels Alder reaction of 2,3-dimethyl-1,3-butadiene and the hetero-dienophile, diethyl azodicarboxylate. Reaction rates in the various solutions were studied using SCRF DFT theory and good agreement with the experimental results was obtained. According to natural bond orbital analysis, it was confirmed that the stabilisation energy of the C-N bonds contributes to the strong interaction between the solvents and transition state (TS) structures. Topological analyses showed a linear correlation between the interaction energy and the sum of electron density at the bond critical point of C-N at the TS. Moreover, with an increase in the overall electron density of the C-N bond critical point, the vibrational frequencies were decreased. Finally, some correlations between the quantum reactivity indices and the rate constants in the presence of 23 solvents were investigated.