In contrast to the THF situation, the monohydrate of THT has been structurally characterised in much detail , also with respect to the water orientation relative to the ring. We are not aware of a complementary vibrational gas phase study and thus consider this to be a valuable diversification of the test set, also in preparation for more challenging thio compounds . In TFE, as in many fluorinated alcohols , the first solvating water acts primarily as a hydrogen bond acceptor, but the symmetric stretching mode is only subtly shifted from the water monomer value by this interaction and by an additional donor contact to the CF 3 group. This provides valuable benchmark information for small complexation shifts, but the IR activity of such weakly perturbed symmetric OH stretching motions in water molecules is low. Therefore, Raman spectroscopy 14 is expected to provide key vibrational information in this case. Structurally, the preference of the monohydrate for an insertion complex is well established and the related, structurally more diverse case of hexafluoroisopropanol is also well studied . By including the simplest model of a peptide co-solvent 85 monohydrate into the vibrational target systems, the characterisation of their unusual biochemical properties can be supported .