Vibrational Spectra of Propionamide and Its C- and N-Deuterated Compounds

Abstract

Abstract The infrared and Raman spectra of CH3CH2CONH2, CH3CD2CONH2 and their N-deuterated compounds in the solid state have been measured. The normal coordinate analysis has been made by assuming the molecular symmetry of Cs. A Urey-Bradley force field was used for the in-plane vibrations and a valence force field for the out-of-plane vibrations of the amide group. The ethyl group was treated by a Urey-Bradley type force field as well as a valence type force field. The assignments of the fundamental frequencies have been made by referring to the infrared and Raman intensities, isotopic frequency shift and the calculated frequencies by using the force constants which were taken from n-paraffins and acetamide. The agreement between the observed and the calculated frequencies in the initial calculation was good for the CH3 and the amide group vibrations but was not good enough for some vibrations involving the α-carbon atom. Only the force constants related to these vibrations were refined by the least squares method in order to obtain the best fit. The calculated frequencies in this way fit to the observed satisfactorily.