Force constants for 3-chloropropyne and chloro-2-butyne

Normal coordinate calculations were carried out for H-C=C-CH₂Cl using a valence force field and the force constants obtained were transferred to CH₃-C=C-CH₂Cl. There seem to be small but significant differences in some of the force constants of the -CH₂Cl group of these two molecules. The vibrational assignment of McLachland 1] is confirmed, and the calculations show that the fundamental vibrations are relatively pure except for the C-C symmetric stretch and the skeletal bends.