Molecular structures, FT-IR and FT-Raman spectra, NBO analysis, NLO properties, reactive sites and quantum chemical calculations of keto–enol tautomerism (2-amino-4-pyrimidinol and 2-amino-pyrimidine-4(1H)-one)

The keto–enol tautomerism of 2-amino-4-pyrimidinol (APN) and 2-amino-pyrimidine-4(1H)-one (APO) are investigated by vibrational spectroscopy and quantum chemical method. FT-IR and FT-Raman spectra are recorded in the regions of 4000–400 cm−1 and 3500–100 cm−1, respectively for APN. Geometrical parameters, vibrational wavenumbers of APN and APO are predicted by density functional theory (DFT) employing B3LYP level with 6-311++G(d,p) and 6-311++G(2d,p) basis sets. The non-linear optical (NLO) properties of the title molecules are computed. The molecular electrostatic potential (MEP) surface maps are plotted and explained in detail. Natural bond orbital (NBO) analyses have been performed on APN molecule. The significant changes in occupancies and the energies of bonding and antibonding orbital have been explained in detail. Thermodynamic properties (heat capacities, entropies, and enthalpy) and their correlations with temperatures are also obtained from the calculated frequencies of the optimized structures. Reactivity descriptors, Fukui functions and electrophilic sites are found and discussed.

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► 2-Amino-4-pyrimidinol and 2-amino-pyrimidine-4(1H)-one are studied using B3LYP level of theory.
► Experimental FT-IR and FT-Raman spectra recorded.
► Non-linear optical properties were studied.
► HOMO, LUMO, local reactivity and chemical reactivity were performed.
► Thermodynamic properties and their correlations with temperature have been obtained.