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 (1)H and (13)C NMR spectra have been recorded. The (1)H and (13)C 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 (β0) 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 σ(∗) 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.