Synthesis, spectroscopic investigations and computational study of monomeric and dimeric structures of 2-methyl-4-quinolinol

Abstract

The present study aimed to determine an efficient and solvent-free method to synthesize 2-methyl-4-quinolinol (2MQ, also known as 4-hydroxy-2-methylquinoline) and includes spectroscopic investigations and computational studies. Molecular geometry and vibrational wavenumbers of 2MQ were investigated using the density functional (DFT/B3LYP) method with 6-311++G(d,p) and 6-311++G(2d,p) basis sets. According to calculations, the keto form of 2MQ is more stable than the annual form, and the dimeric conformation is predicted to be more stable than the monomeric conformations. A detailed analysis of the nature of the hydrogen bonding, using topological parameters such as electronic charge density, Laplacian, kinetic and potential energy density evaluated at the bond critical point, is also presented. The 1H nuclear magnetic resonance chemical shifts of the molecule were calculated by the GIAO method. The molecule orbital contributions were studied by using total (TDOS) and partial (PDOS) density of states. The UV–visible spectrum of the compound was recorded and the electronic properties, such as HOMO and LUMO energies, were investigated by the time-dependent DFT (TD-DFT) approach. The linear polarizability (α) and the first-order hyperpolarizability (β) values of the investigated molecule were computed using DFT quantum mechanical calculations. The results show that the 2MQ molecule may have a nonlinear optical comportment with non-zero values. The stability and charge delocalization of the molecule was studied by natural bond orbital analysis. In addition, a molecular electrostatic potential map of the title compound was studied for predicting the reactive sites. Local reactivity descriptors, such as Fukui functions, local softness and electrophilicity indices analyses, were studied to determine the reactive sites within the molecule.