Implicit and explicit solvent effects on the selectivity of the cycloaddition reaction of cyclopentadiene and methyl acrylate; a theoretical study

Abstract

The product selectivity of the Diels-Alder reaction between cyclopentadiene and methyl acrylate has been studied through a solvent effect analysis by implicit and explicit solvent models. Two paths for this reaction have been proposed and thermodynamic and kinetic parameters for each path were calculated by the B3LYP functional with 6-311++G(d,p) basis set at 298.15 K. In the explicit solvent model, hydrogen bonds were investigated by the QM/MM method. According to the results, the proportion of the exo product in the gas phase is more than for the endo one, which is in contrast to the solvent phase. HOMO-LUMO analyses in the gas phase and different solvents have been done and solvent effects on the energies of the HOMO-LUMO orbitals were investigated. According to the results, the band gap of the TSs was increased in the presence of the solvents. Finally, natural population analysis has been performed to calculate the electronic charges of some atoms that are involved in the centre of the reaction. The data obtained showed that different solvents, including polar and nonpolar solvents, have different effects on the electronic charges of the atoms. Topological analysis of the structures during the reaction by the quantum theory of atoms in molecules (QTAIM) method in the gas phase and different solvents confirmed a cyclic structure for the transition state.

Understanding the role of noncovalent interactions on the rate of some Diels‐Alder reactions in different solvents

“…Calculated bond lengths of the reactants and TSs at M06‐2X level, Table S1, reveal that the average CC bond lengths at the TSs of the reactions A, B, and C (TSA, TSB, TSC) are 2.30, 2.25, and 2.25 Å, respectively, which are according to the previously reported data …”

“…Diels and Alder (DA) reactions in organic chemistry have many applications to synthesis new compounds and materials . They have several subclasses and different parameters, such as temperature, solvents and pressure have an important effect on the rate and mechanism of these reactions . In recent years, qualitative aspects of the solvent effects on the rate or selectivity and mechanism of the reactions have been investigated by employing theoretical and experimental methods .…”

“…In the previous studies, we theoretically investigated the solvent effects on different cycloaddition and electrocyclic reactions. By employing quantum chemistry calculations, solvent effects were analyzed on the kinetics and mechanism of cycloaddition reaction between cyclopentadiene and methyl acrylate . The obtained results indicate that endo product proportion in the solution phase is more than exo product in comparison with gas phase.…”

“…The obtained results indicate that endo product proportion in the solution phase is more than exo product in comparison with gas phase. Moreover, theoretical studies on different cycloaddtions reactions indicated that solvents have remarkable effects on the charge transfer, molecular orbital interactions, kinetic and thermodynamic parameters, IR vibrational frequencies at the TSs, topological parameters at the bond critical points and mechanism of the reaction . Although, in all cases, a change in the mentioned parameters was described in the presence of the solvent in comparison with gas phase, while our aim here, is to determine the nature of the solvent effects on different types of cycloaddition reactions (composed of different reactants) from the molecular viewpoint through the noncovalent interaction analysis.…”