The Steric Effects of Alkyl Groups on the N–H Stretching Vibrations and the Rotational Isomerism of Alkylureas

Publisher Website
Google Scholar
Abstract
The free N–H stretching vibrations of various trialkylureas, R2UR′, in dilute solutions were studied in order to resolve our questions concerning the rotational isomerism of dialkylureas. In the infrared spectrum of R2UR′, where R is isopropyl or cyclohexyl, an additional N–H band appears on the higher-frequency side of the trans N–H band. It was also observed that the larger the effective size of the R′ group on R2UR′ is, the stronger the intensity of the additional band becomes. It was concluded, in connection with the rotational isomerism of dialkylureas, that the additional band arises from a form in which the N–H group is out of the skeletal plane.