The interpretation of the infra-red and Raman spectra of the n -paraffins

Abstract Infra-red spectra of a series of crystalline n-paraffins containing an odd number of carbon atoms have been obtained. The spectrum of oriented crystals of n-nonadecane has also been examined. These new experimental results have been combined with the earlier data on the crystalline n-paraffins containing an even number of carbon atoms, and many series of absorption bands have been identified in the complete set of spectra. These regularities, as well as those present in the Raman spectra, have been interpreted in terms of CH2, CH3, and C—C stretching vibrations. Very regular distributions of frequencies have been found between 720 and 1030 cm-1 and between 1200 and ca. 1370 cm-1, which are assigned to CH2 rocking and wagging vibrations, respectively. The majority of the absorption bands between 1150 and 880 cm-1 can be attributed to C—C stretching or CH3 rocking modes, and assignments are suggested for the principal series observed in this region.