FT-IR, FT-Raman spectra, density functional computations of the vibrational spectra and molecular geometry of butylated hydroxy toluene

The FT-IR spectrum of 2,6-di-tert-butyl-4-methylphenol [butylated hydroxy toluene] was recorded in the region 4000–400 cm−1. The FT-Raman spectrum of butylated hydroxy toluene was also recorded in the region 3500–50 cm−1. The molecular structure and vibrational frequencies of butylated hydroxy toluene (BHT) have been investigated with combined experimental and theoretical study. Two stable conformers of the title compound were obtained from the result of geometry optimizations of these possible conformers. The conformer 1 is (approximately 2.6 kcal/mol) more stable than conformer 2. Geometry optimizations and vibrational frequency calculations were performed by BLYP and B3LYP methods using 6-31G(d), 6-31G(d,p) and 6-31+G(d,p) as basis sets. The scaled frequencies were compared with experimental spectrum and on the basis of this comparison; assignments of fundamental vibrational modes were examined. Comparison of the experimental spectra with harmonic vibrational wavenumbers indicates that B3LYP/6-31G(d) results are more accurate. Predicted electronic absorption spectra of BHT from TD-DFT calculation have been analyzed and compared with the experimental UV–vis spectrum. The calculated HOMO and LUMO energies show that the charge transfer occurs within the molecule.

Figure optionsDownload as PowerPoint slideHighlights
► Molecular geometry and vibrational assignments were carried out for BHT.
► PES scan was performed for the dihedral angle C5–C6–C11–C12.
► All the calculations were performed by using BLYP and B3LYP methods.
► TD-DFT calculation was also carried out for BHT molecule.