Molecular structure, vibrational spectra and 13C and 1H NMR spectral analysis of 1-methylnaphthalene by ab initio HF and DFT methods

• FT-IR and FT-Raman spectra of 1-methylnaphthalene in the solid phase are recorded and analyzed.
• The optimized geometry and vibrational wavenumbers are computed using HF and DFT methods.
• The complete vibrational assignment and spectroscopic analysis have been carried out.
• The HOMO, LUMO energy gap is theoretically predicted.
• The NBO analysis explains the intramolecular hydrogen bonding.

The Fourier transform infrared (FT-IR) and FT-Raman of 1-methylnaphthalene (1MN) have been recorded and analyzed. The equilibrium geometry, bond lengths, bond angles and harmonic vibrational frequencies have been investigated with the help of density functional theory (DFT) method. Vibrational spectroscopic assignments of 1-methylnaphthalene (1MN) are carried out with the help of quantum chemical calculation. The 1H and 13C nuclear magnetic resonance (NMR) chemical shifts of the molecule are calculated by the Gauge including atomic orbital (GIAO) method. The molecular stability and bond strength have been investigated by using natural bond orbital analysis (NBO). The assignments of vibrational spectra have been carried out with the help of normal co-ordinate analysis (NCA) following the scaled quantum mechanical force field (SQMFF) methodology. The 1H and 13C nuclear magnetic resonance (NMR) chemical shift of the molecular is depend only on the structure of the molecule. The calculated HOMO and LUMO energy shows that charge transfer interactions take place within the molecule. Finally, the calculation results are applied to simulate infrared and Raman spectra of the title compound which show good agreement with observed spectra.

A complete vibrational analysis of 1-methylnaphthalene is performed by combining the experimental and theoretical information using density functional theory (DFT) based on scaled quantum chemical approach. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. Comparison of simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes.Figure optionsDownload as PowerPoint slide