Low frequency modes in molecular crystals. XIX. Methyl torsions and barriers to internal rotation of some three top molecules with C3 symmetry

The low frequency infrared spectra of $({\mathrm{CH}}_3{)}_3\mathrm{COH,}\mathrm{\hspace{0.17em}(}{\mathrm{CD}}_3{)}_3\mathrm{COH,}\mathrm{\hspace{0.17em}(}{\mathrm{CH}}_3{)}_3\mathrm{CSH,}\mathrm{\hspace{0.17em}(}{\mathrm{CH}}_3{)}_3\mathrm{CNCO,}\mathrm{\hspace{0.17em}(}{\mathrm{CH}}_3{)}_{3^{-}}\mathrm{CNCS,}\mathrm{\hspace{0.17em}(}{\mathrm{CH}}_3{)}_3\mathrm{CCHO,}\mathrm{\hspace{0.17em}(}{\mathrm{CH}}_3{)}_3{\mathrm{CNH}}_2\mathrm{,\hspace{0.17em}(}{\mathrm{CH}}_3{)}_3{\mathrm{COCH}}_3$ and (CH₃)₃CODC₃ have been recorded for these molecules in both the gaseous and solid states. Harmonic barriers have been calculated for t‐butyl methyl group rotation from frequencies measured for the compounds in their solid state. The values are 4.13, 4.52, 4.41, 4.67, 4.86, 3.96, 4.28, 4.71, and 4.55 kcal/mole, respectively. Estimates of the periodic barriers to rotation of the tertiary butyl groups were also determined for $({\mathrm{CH}}_3{)}_3\mathrm{COH}\text{(∼ 1\hspace{0.17em}}\mathrm{kcal/mole}\mathrm{),\hspace{0.17em}(}{\mathrm{CH}}_3{)}_3\mathrm{CSH}\text{\hspace{0.17em}(1.5\hspace{0.17em}}\mathrm{kcal/mole}\mathrm{),\hspace{0.17em}(}{\mathrm{CH}}_3{)}_3\mathrm{CNCO}\text{\hspace{0.17em}(0.3\hspace{0.17em}}\mathrm{kcal/mole}\mathrm{),\hspace{0.17em}(}{\mathrm{CH}}_3{)}_3\mathrm{CNCS}\text{\hspace{0.17em}(1.3\hspace{0.17em}}\mathrm{kcal/mole}\mathrm{),\hspace{0.17em}(}{\mathrm{CH}}_3{)}_3\mathrm{CCHO}\text{\hspace{0.17em}(0.7\hspace{0.17em}}\mathrm{kcal/mole})$ , and (CH₃)₃COCH₃ (3.57 kcal/mole) from the observed fundamentals in the infrared spectra of the gases.