Spectroscopic investigation, natural bond orbital analysis, HOMO–LUMO and thermodynamic functions of 2-tert-butyl-5-methyl anisole using DFT (B3LYP) calculations

• Experimental FT-IR and FT-Raman spectra were recorded for 2-tert-butyl-5-methyl anisole.
• Theoretical spectra were interpreted with the aid of normal coordinate analysis.
• NBO, HOMO–LUMO, MEP and thermodynamic properties were also studied.

The optimized molecular structure and corresponding vibrational assignments of 2-tert-butyl-5-methyl anisole (TBMA) have been investigated using density functional theory (DFT)/B3LYP with 6-31G(d,p) and 6-311++G(d,p) basis sets investigation of the relative orientation of the methoxy group has shown two conformers (O-cis) and (O-trans) exist. The vibrational analysis of the stable conformer of the title compound is performed by means of infrared absorption and Raman spectroscopy in combination with theoretical simultaneously. The natural bond orbital (NBO) analysis is useful to understand the intra-molecular hyper conjugative interaction lone pair and π∗(CC), σ∗(CH) bond orbital. HOMO and LUMO energies show that charge transfer occurs in the molecule, therefore; HOMO, LUMO and molecular electrostatic potential (MEP) were calculated and analyzed. 1H and 13C NMR spectra by using gauge including atomic orbital (GIAO) method of studied compound were compared with experimental data. The thermodynamic functions of TBMA were calculated by B3LYP/6-311+G(d,p) basis set.

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