The manifestation of hydrogen bonding in the IR spectra of dl-threitol and erythritol (300–20 K)

The infrared (4000–400 cm−1) and, in part, Raman spectra were recorded for the two isomeric polycrystalline sugar alcohols, dl-threitol and erythritol. Samples were pure substances and isotopically diluted OH/OD compounds. IR spectra were recorded in the 300–20 K range. Assignment of hydrogen bond structure sensitive out-of-plane bending vibrational modes for OH/OD-groups of different H-bond systems is based on isotope exchange and temperature variations. At least seven bands for threitol and two for erythritol correspond to differently H-bonded OH/OD-groups. Relative strengths and quantity of different H-bonds were evaluated. Unlike erythritol, threitol contains over 5% of weak H-bonds. The formation from the melt of a crystalline racemate as a molecular compound of d- and l-forms is suggested. Comparisons with previous neutron scattering results are discussed. In solution, all four OH-groups of both tetritols form H-bonds of equal strength in accord with the basicity of the solvent.