Experimental and density functional theory study on structure, vibrational and molecular characteristics of 2-chloro-5-methylpyrimidine and 2,4-dichloro-5-methylpyrimidine

ABSTRACT

This study deals with the determination of torsional potentials, optimised geometry in monomer and dimer form for gas phase for the molecular ground state and vibrational assignments of 2-chloro-5-methyl pyrimidine; and 2,4-dichloro-5-methyl pyrimidine carried out by density functional theory employing B3LYP exchange and correlational functional in conjunction with 6-311++G(d,p) basis set using quantum chemical calculations. The existence of inter-molecular hydrogen bonds was also predicted. Fourier Transform infrared and Fourier Transform Raman spectra were recorded and vibrational analysis of the molecules was made using potential energy distribution and eigen vectors obtained in the computations. Observed and calculated frequencies agreed with an rms error 10.03 and 10.0 cm⁻¹ for 2-chloro-5-methyl pyrimidine and 2,4-dichloro-5-methyl pyrimidine, respectively. Electronic transitions were analysed using experimental and simulated Ultraviolet–Visible spectra of the two molecules wherein polarisable, continuum model in solvent phase was used for simulations. Molecular characteristics like highest occupied molecular orbital, lowest unoccupied molecular orbital, molecular electrostatic surface potential and thermodynamic parameters were also investigated. Stability of the molecules arising from hyper conjugative interactions, charge delocalisation has been analysed using natural bond orbital analysis.

KEYWORDS:

• Chloro-methylpyrimidine
• DFT
• HOMO–LUMO
• NBO
• MESP

Acknowledgements

The authors sincerely acknowledge Sophisticated Analytical Instrumentation Facility (SAIF), IIT Madras, Chennai, India, for spectral measurements (IR &Raman). They are also grateful to NIPER, Hyderabad, for recording UV-Visible spectra.

Disclosure statement

No potential conflict of interest was reported by the author(s).