It is shown that steric repulsions stabilize one of the three rotational isomers of 2 : 3-dibromobutyric acid at the expense of the others. The high resolution proton magnetic resonance spectra may be analysed as ABX3systems, but preferential solvent shifts cause the observed patterns to change drastically with solvent. The spin coupling between the methyl group and the proton in the gauche configuration, an interaction over four chemical bonds, is found to be -0·35 c/s.