Infrared studies of rotational isomerism in α-halogeno-acetamides

Infrared spectra of fluoroacetamide, chloroacetamide, and iodoacetamide have been recorded in the solid, liquid, and vapour phases in the region 4000–200 cm^?1. A complete vibrational frequency assignment of the fundamental and non-fundamental bands has been made for each of these molecules. The results show that each of these compounds exists as an equilibrium mixture of gauche and trans isomers. Enthalpy differences (ΔH) between these isomers were calculated for each of these compounds in the liquid and vapour phases. The trans form is the most stable of the rotational isomers in all three phases.