Study of vibrational spectra, normal coordinate analysis and molecular structure of 6-(2,3-dichlorophenyl)-1,2,4-triazine-3,5-diamine using density functional theory

• Vibrational assignments with PED of DCTDA were calculated.
• Potential energy surface scan with the B3LYP/6-311G(d,p) level of theoretical approximations was performed.
• NLO, NBO and HOMO and LUMO energies of DCTDA were studied.

In the present analysis, the FT-IR, FT-Raman spectra of 6-(2,3-dichlorophenyl)-1,2,4 triazine-3,5-diamine (DCTDA) have been recorded in the region 4000–450 cm−1 and 4000–100 cm−1 respectively. The stable structure geometry of the isolated molecule in the gas phase was investigated theoretically using density functional theory (B3LYP) with 6-311G(d,p) basis set. The assignment of the vibrational spectra has been calculated to aid with normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMF). UV–Vis spectra of the compound was recorded in water solvent and the electronic properties, such as HOMO and LUMO energies were calculated by time-dependent density functional theory (TD-DFT) approach. The various intramolecular interactions which are responsible for the stabilization of the molecule were revealed by the natural bond orbital analysis. The molecule orbital contributions are studied by density of energy states (DOS). The other molecular properties like molecular electrostatic potential (MEP), NLO and thermodynamic properties of the title compound at different temperatures have been calculated. Finally the calculation results were applied to stimulate infrared and Raman spectra of the title compound which show good agreement with observed spectra.

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