The methyl torsion in toluene (h8, d8) and nitromethane (h3, d3) in the polycrystalline state

Abstract

The Raman spectra of toluene and nitromethane at about −150 °C were observed in the region of 10–250 cm⁻¹. In toluene‐h₈ two weak and sharp bands observed at 77 and 115 cm⁻¹ were assigned to the CH₃ torsion. In toluene‐d₈ the CD₃ torsion was not observed distinctly. The assignment was confirmed by the calculation of the torsional energy levels on the basis of the C_2v symmetry by the finite element method. The potential function was assumed to be Σ1/2V_n(1−cosnβ) (n=2, 6, and 12). The best fit was obtained when V₂, V₆, and V₁₂ were 28, 99, and −42 cm⁻¹, respectively, and further confirmed that the other structures observed at 106 and 94 cm⁻¹ could be also assigned to the CH₃ torsion. In nitromethane‐h₃ or ‐d₃ a very weak and broad band observed at 148 or 132 cm⁻¹, respectively, was assigned to the methyl torsion. In the process of the adjustment of the potential constants it was found that V₃ was important. The best fit was obtained when V₃, V₆, and V₁₂ were 210, 150, and 30 cm⁻¹, respectively. This shows that a sort of association takes place between a hydrogen atom of a molecule and an oxygen atom of the other.