Rotational isomerism and barriers to internal rotation in hydroxyacetonitrile from microwave spectroscopy

Abstract

The microwave spectra of HOCH₂CN and DOCH₂CN show that the molecule exists as the gauche rotamer in the gas phase. A large number of intense lines converging to a band head near 16 800 MHz for DOCH₂CN and 110 700 MHz for HOCH₂CN are attributed to the v= 1 â†� 0 transitions of the hydroxyl torsion. The rotational constants indicate that α_e, the angle between the HOC and OCC planes at the potential minima is approximately 123° from the trans position. Potential functions which reproduce the observed v= 1 â†� 0 torsional frequencies have been obtained for 106° < α_e < 116° and show there is a barrier of 270 ± 50 cm^–1 at the cis position and one of 570 ± 200 cm^–1 at the trans position. The rotational constants calculated from a molecular model and the potential functions indicate that α_e is probably closer to 116° than 106°.