Theoretical Study on Imidazopyridinyl-chalcones based Dimers Mechanism of Formation Using Quantum Chemistry Methods

Abstract

Imidazo[1,2-a]pyridinyl-chalcones (IPCs) offer a broad spectrum of biological activities with molecular diversity possible by synthesis. Two potential reactive sites were identified within their basic molecular skeleton from which obtaining dimers by synthesis is possible. In this study, at the level B3LYP/6-311G(d), work focused on elucidating both the mode of bond formation between the two reactive sites and the concerted course of dimerization reaction in the IPC series according to the concepts and tools of transition state theory. Four substituted IPC molecules with stronger nematicidal activity were used in addition to the unsubstituted IPC molecule as monomers. Calculations performed on each initial reactive system modelled using two IPCs led to a unique transition structure in each case. Molecular dimerization in IPC series was found to follow a one-step reaction mechanism. It involved the formation of two covalent bonds, C5–C14׳, and C14–C29׳. The stabilization of the second bond was faster than the first which, moreover, required less energy for establishment. Analysis of bond lengths confirmed the stability of the bonds formed. The energy parameters and the characteristics of the reaction path proved the stability of the dimers envisaged with respect to the reagents used. The path of dimerization reaction in the IPC series was found to be substitution independent but the activation energies depended on the overall nucleophilicity of monomers.