A comparative study on vibrational, conformational and electronic structure of 2-chloro-4-methyl-3-nitropyridine and 2-chloro-6-methylpyridine

Experimental FTIR and FT-Raman spectroscopic analysis of 2-chloro-4-methyl-3-nitropyridine (2C4M3NP) and 2-chloro-6-methylpyridine (2C6MP) have been performed. A detailed quantum chemical calculations have been carried out using B3LYP and B3PW91 methods with 6-311++G** and cc-pVTZ basis sets. Conformation analysis was carried for 2C4M3NP and 2C6MP. The temperature dependence of thermodynamic properties has been analysed. The atomic charges, electronic exchange interaction and charge delocalisation of the molecule have been performed by natural bond orbital (NBO) analysis. Molecular electrostatic surface potential (MESP), total electron density distribution and frontier molecular orbitals (FMOs) are constructed at B3LYP/6-311++G** level to understand the electronic properties. The charge density distribution and site of chemical reactivity of the molecules have been obtained by mapping electron density isosurface with electrostatic potential surfaces (ESP). The electronic properties, HOMO and LUMO energies were measured by time-dependent TD-DFT approach.

The FT-IR and FT-Raman spectra of 2-chloro-4-methyl-3-nitropyridine (2C4M3NP) and 2-chloro-6-methylpyridine (2C6MP) were recorded and complete assignments of the observed spectra have been proposed. DFT calculations have been performed and the structural parameters of the compounds were determined from the optimised geometry with 6-311++G(d,p) and cc-pVTZ basis sets and giving energies, harmonic vibrational frequencies, depolarisation ratios, IR and Raman intensities. The influences of chlorine, methyl and nitro groups on the skeletal modes have been investigated. A detailed natural bond orbital analysis was also carried out.Figure optionsDownload as PowerPoint slideHighlights
► FTIR and FT-Raman investigations of 2-chloro-4-methyl-3-nitropyridine and 2-chloro-6-methylpyridine were carried out.
► Conformational analysis was performed to determine the stale geometry.
► Energy, structural, thermodynamical and vibrational characteristics were determined.
► The electronic properties and NBO analysis were carried out.
► Effects of chlorine, methyl and nitro groups on the pyridine ring parameters have been analysed.