Quantum chemical calculations on elucidation of molecular structure and spectroscopic insights on 2-amino-4-methoxy-6-methylpyrimidine and 2-amino-5-bromo-6-methyl-4-pyrimidinol - A comparative study

The FTIR and FT-Raman spectra of 2-amino-4-methoxy-6-methylpyrimidine (AMMP) and 2-amino-5-bromo-6-methyl-4-pyrimidinol (ABMP) have been recorded in the region 4000-450 and 4000-100 cm(-1), respectively. The optimized geometry, frequency and intensity of the vibrational bands of AMMP and ABMP were obtained by the density functional theory (DFT) using 6-311++G** basis set. The harmonic vibrational frequencies were calculated and the scaled values have been compared with experimental FTIR and FT-Raman spectra. The observed and the calculated frequencies are found to be in good agreement. The H-1 and C-13 NMR spectra have been recorded. The H-1 and C-13 nuclear magnetic resonance chemical shifts of the molecule were also calculated using the gauge independent atomic orbital (GIAO) method. The theoretical UV-visible spectrum of the compound using TD-DFT method and the electronic properties, such as HOMO and LUMO energies, are performed by time-dependent DFT (TD-DFT) approach. The calculated HOMO and LUMO energies show that charge transfer occurs within molecule. The first order hyperpolarizability (beta(0)) and its related components of AMMP and ABMP are calculated using DFT/6-311++G** method on the finite-field approach. The natural atomic charges of the molecules were also discussed. The change in electron density (ED) in the sigma* antibonding orbitals and stabilization energies E(2) have been calculated by natural bond orbital (NBO) analysis to give clear evidence of stabilization originating in the hyper conjugation of hydrogen-bonded interactions. (C) 2014 Elsevier B.V. All rights reserved.