On the factors affecting tautomerism: consequences of N-substituents (Me/NR2) in structures derived from salicylaldimines

Abstract

This computational organic chemistry study was performed using the B3LYP and the Hartree–Fock methods. Other methods were compared using two model compounds, and these methods are: second-order Møller–Plesset, fourth-order Møller–Plesset, quadratic configuration interaction with single and double excitation and coupled cluster single and double excitations. The study included discussions of the following aspects: the molecular structures, the harmonic oscillator measure of aromaticity, the energy differences between the tautomers, selected infrared stretching frequencies, the atomic charges (Mulliken and natural population analysis), selected NMR chemical shifts, the molecular orbital diagrams and the R groups. The calculations revealed that the electronic structure of salicylaldimines is sensitive to this substitution and may change the physical organic aspects including tautomerism significantly. The results illustrate that the proton–electron delocalisation as a sub-molecular event might be a controllable process when a powerful H-bond exists. This is a new discovery in the area of tautomerism-based functional materials that will help in fine-tuning their properties.