Vibrational analysis of 1,2-dichloroalkanes

IR and Raman spectra have been obtained for 1,2-dichlorobutane and 1,2-dichloro- pentane. The butane crystallizes in the P_XS_XH conformation, but the pentane could not be made to crystallize. Normal coordinate calculations were made for the P_XS_XH, P_CS_HH, and P_HS_HH conformers of these two compounds and for 1,2-dichloropropane. The ob- served spectra were interpreted with the aid of these calculations, and it was concluded that all three conformers exist for each of these compounds. The force field that was obtained should be applicable to other 1,2-dichloroalkanes.