FT-IR, FT-Raman, ab initio and DFT structural, vibrational frequency and HOMO–LUMO analysis of 1-naphthaleneacetic acid methyl ester

In this work, the FT-IR and FT-Raman spectra of 1-naphthaleneacetic acid methyl ester (abbreviated as 1-NAAME, C10H7CH2CO2CH3) have been recorded in the region 3600–10 cm−1. The optimum molecular geometry, normal mode wavenumbers, infrared and Raman intensities, Raman scattering activities, corresponding vibrational assignments, Mullikan atomic charges and other thermo-dynamical parameters were investigated with the help of HF and B3LYP (DFT) method using 6-31G(d,p), 6-311G(d,p) basis sets. Reliable vibrational assignments were made on the basis of total energy distribution (TED) calculated with scaled quantum mechanical (SQM) method. From the calculations, the molecules are predicted to exist predominantly as the C1 conformer. The correlation equations between heat capacity, entropy, enthalpy changes and temperatures were fitted by quadratic formulae. Lower value in the HOMO and LUMO energy gap explains the eventual charge transfer interactions taking place within the molecule. UV–VIS spectral analyses of 1NAAME have been researched by theoretical calculations. In order to understand electronic transitions of the compound, TD-DFT calculations on electronic absorption spectra in gas phase and solvent (DMSO and chloroform) were performed. The calculated frontier orbital energies, absorption wavelengths (λ), oscillator strengths (f) and excitation energies (E) for gas phase and solvent (DMSO and chloroform) are also illustrated.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Molecular geometry and vibrational frequencies of 1-naphthalneacetic acid methyl ester were calculated. ► The calculated DFT results were compared with both FT-IR and FT-Raman data. ► The electronic properties, such as HOMO and LUMO energies, absorption wavelength and excitation energies, were performed by time-dependent DFT (TD-DFT) approach for different solvents. ► The thermodynamic properties (heat capacity, entropy and enthalpy changes) of the title compound at different temperatures have been calculated by the theoretical vibrational analysis.