Vibrational frequencies, structural confirmation stability and HOMO–LUMO analysis of nicotinic acid ethyl ester with experimental (FT-IR and FT-Raman) techniques and quantum mechanical calculations

The FT-IR and FT-Raman spectra of nicotinic acid ethyl ester (abbreviated as NAEE, C8H9NO2) have been recorded in the region 3600–10 cm−1. Potential energy curve was computed by means of scanning CCCO torsion angle. The optimized geometric parameters geometry optimization and the energies associated possible two conformers (C1 and C2) were computed. The computational results diagnose the most stable conformer of NAEE as the C1 form. The optimum molecular geometries, energies, normal mode wavenumbers, infrared and Raman intensities, corresponding vibrational assignments, atomic charges, HOMO–LUMO analysis and thermo-dynamical parameters were investigated with the help of HF, B3LYP and LSDA methods with 6-311G(d,p) and 6-311G++(d,p) basis sets. Reliable vibrational assignments were made on the basis of total energy distribution (TED) calculated with scaled quantum mechanics (SQM) method. Thermodynamic properties of the title compound at different temperatures were calculated. The results of the calculations were applied to simulate infrared and Raman spectra of the title compound which show excellent agreement with the observed spectra.