Conformational, structural, vibrational and quantum chemical analysis on 4-aminobenzohydrazide and 4-hydroxybenzohydrazide – A comparative study

Experimental and theoretical quantum chemical studies were carried out on 4-hydroxybenzohydrazide (4HBH) and 4-aminobenzohydrazide (4ABH) using FTIR and FT-Raman spectral data. The structural characteristics and vibrational spectroscopic analysis were carried performed by quantum chemical methods with the hybrid exchange-correlation functional B3LYP using 6-31G**, 6-311++G** and aug-cc-pVDZ basis sets. The most stable conformer of the title compounds have been determined from the analysis of potential energy surface. The stable molecular geometries, electronic and thermodynamic parameters, IR intensities, harmonic vibrational frequencies, depolarisation ratio and Raman intensities have been computed. Molecular electrostatic potential and frontier molecular orbitals were constructed to understand the electronic properties. The potential energy distributions (PEDs) were calculated to explain the mixing of fundamental modes. The theoretical geometrical parameters and the fundamental frequencies were compared with the experimental. The interactions of hydroxy and amino group substitutions on the characteristic vibrations of the ring and hydrazide group have been analysed.

Graphical abstractThe complete vibrational analyses of the fundamental modes of 4-hydroxybenzohydrazide (4HBH) and 4-aminobenzohydrazide (4ABH) molecules were performed. The experimental parameters were compared with the theoretical parameters of the compounds determined from the DFT–B3LYP gradient calculations employing the 6-31G**, 6-311++G** and aug-cc-pVDZ basis sets. The effect of substituents NH2 and OH in the benzohydrazide moiety have been analysed and compared. The kinetic and thermodynamic stability and chemical hardness of the molecules have been determined. The reactive centres were found from the molecular electrostatic potential of the molecules.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The vibrational analysis of 4-hydroxybenzohydrazide and 4-aminobenzohydrazide were performed. ► The experimental parameters were compared with DFT–B3LYP calculations. ► The effect of NH2 and OH in the benzohydrazide moiety have been analysed. ► Kinetic and thermodynamic stabilities and chemical hardness of the molecules were determined. ► The reactive centres were found from the electrostatic potential of the molecules.