Cryogenic Solutions as a Tool to Characterize Red-and Blue-Shifting C–H···X Hydrogen Bonding

During recent years, solutions in liquefied inert gases have proven to be an ideal medium to study molecular complexes involving C–H···X (with X = O, N, F, π, etc.) red- or blue-shifting hydrogen bonds. In this chapter, the experimental setups for the infrared and Raman studies of cryosolutions are described, and the general methodologies used to study weakly bound molecular complexes are discussed. The methods are illustrated using data obtained for a variety of C–H···X hydrogen-bonded complexes involving the mixed haloforms CHCl _x F_3-x and halothane CF₃CBrClH.