Hydrogen Bonding Interactions in Three 2-Mercaptoethanol Systems: An Excess Infrared Spectroscopic Study

The hydrogen bonding properties of a representative molecule, 2-mercaptoethanol (ME), of which two functional groups OH and SH are believed to interact competitively or selectively with proton-accepting molecules, have been studied. Three binary systems, namely ME-CCl4, ME-dimethyl sulfoxide (DMSO), and ME-acetone, were investigated with excess infrared absorption spectroscopy. It is found that when DMSO or acetone is added into ME, they preferentially form hydrogen bonds with OH, and the hydrogen bonds in the ME-DMSO system are stronger than those in the ME-acetone system. When CCl4 is added into ME, the weak hydrogen bonds involving the SH group are broken preferentially with increasing CCl4 concentration. The dissociation process of ME in the inert diluent CCl4 over the entire concentration range has been discussed in detail. In the very low concentration range of CCl4, the highly hydrogen bonded ME multimers mainly break into medium-sized aggregates. The amount of the trimers and dimers first increases and then, at x(CCl4) = 0.77, begins to decrease. These results suggest that excess infrared spectroscopy can provide detailed molecular pictures in liquid solutions containing complex hydrogen bonding interactions. It can also help to locate individual peak positions in the deconvolution of overlapped absorption bands.