The infra-red spectrum of dimethylacetylene and the torsional barrier

Abstract
The perpendicular C—H stretching band of dimethylacetylene is studied theoretically. It is shown that the doubling of the main peaks observed by Mills & Thompson (1954) is probably due to vibrational coupling between the two methyl groups. The torsional barrier is estimated to be not greater than about 10 cm -1 , and it is shown how the barrier could be accurately evaluated from a somewhat better-resolved infra-red spectrum.