Published volumetric mixing data for DMSO-n-alcohol systems show a transition from attractive to repulsive interaction dominance for increasing alkyl chain length. A spectroscopic marker for the relative dominance of these interactions is investigated by FTIR measurements. While most vibrational modes show very similar behavior for the alcohols (C3-C5) studied, the CO torsion mode reveals a strong correlation between maximum red-shift and the balance of attraction and repulsion.