The effect of pressure on charge-enhanced C–H⋯O interactions in aqueous triethylamine hydrochloride probed by high pressure Raman spectroscopy

The weak hydrogen bonding structures of protonated triethylamine in aqueous solution were investigated by Raman spectroscopy as a function of hydrostatic pressure. The formation of a weak hydrogen bond was directly evidenced by a low-frequency shift of the hydrogen-bonded C–H stretches in the protonated triethylamine moiety. For pure triethylamine, an increase in pressure leads to a blue frequency shift of the C–H bands. Nevertheless, the high pressure study of the C–H bands for a dilute protonated triethylamine/D2O solution yielded an unusual nonmonotonic pressure dependence. This result indicates charge-enhanced C–H⋯O hydrogen-bond formation at high pressure.