Low frequency modes in molecular crystals. XIX. Methyl torsions and barriers to internal rotation of some three top molecules with <i>C</i>3 symmetry

Abstract

The low frequency infrared spectra of (CH3)3COH, (CD3)3COH, (CH3)3CSH, (CH3)3CNCO, (CH3)3−CNCS, (CH3)3CCHO, (CH3)3CNH2, (CH3)3COCH3 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 (CH3)3COH(∼ 1 kcal/mole), (CH3)3CSH (1.5 kcal/mole), (CH3)3CNCO (0.3 kcal/mole), (CH3)3CNCS (1.3 kcal/mole), (CH3)3CCHO (0.7 kcal/mole), and (CH3)3COCH3 (3.57 kcal/mole) from the observed fundamentals in the infrared spectra of the gases.