1H NMR and IR spectra of methyl dichloropropanoates and butanoates

Methyl dichloropropanoates and butanoates were synthesized and their ¹H NMR and IR spectra were studied. Comparisons were made with the spectral characteristics of corresponding monochlorocompounds. Special attention was given to the elucidation of the characteristic spectral features associated with particular chlorine substitution patterns. The ¹H NMR of erythro and threo methyl 2,3-dichlorobutanoates were analyzed using a computer program MAOCON, a modified LAOCOON 3 program. In the spectrum of the threo form the order of the chemical shifts of protons on asymmetric carbons seems to be opposite to that reported in earlier literature. Also vicinal coupling constants J₂₃ were found to be greater than those reported earlier.