Tautomers of 2,4-dihydro-3H-1,2,4-triazol-3-one and their Composites with NTO - A DFT Treatment

In the present density functional study, some tautomers of 2,4-dihydro-3H-1,2,4-triazol-3-one (1,2-dihydro-1,2,4-triazol-3-one) and their composites formed with NTO have been considered within the constraints of the density functional theory and the basis set employed (B3LYP/6-311++G(d,p)). The triazolone considered is the precursor of NTO in various methods. It may exhibit 1,3-proton tautomerism. Various energies, QASR, quantum chemical and spectral properties have been harvested and discussed. All the considered species have exothermic heat of formation and favorable Gibbs free energy of formation values at the standard states and they are stable electronically. Although most of the composites considered exhibit a directed interaction between their partners, one of them possesses perpendicular (T-type) orientation. Certain hydrogen bondings between the tautomers and NTO occur at different extents, depending on the particular tautomer involved in the composite. Both of the components have hydrogen bond donor and acceptor properties except composite NTO+T2, in which the tautomer is the hydrogen bond donor and NTO is the acceptor. The tautomers absorb in the UV region of the spectrum like NTO, whereas in all the composites appreciable changes in the appearance of the spectra happen and certain degree of bathochromic effect occurs as compared to the respective spectra of the partners.