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.