The manifestation of hydrogen bonding in the IR spectra of DL-threitol anderythritol (300-20 K)

The infrared (4000-400 cm(-1)) and, in part, Raman spectra were recorded fo r the two isomeric polycrystalline sugar alcohols, DL-threitol and erythrit ol. 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-group s of different H-bond systems is based on isotope exchange and temperature variations. At least seven bands for threitol and two for erythritol corres pond to differently H-bonded OH/OD-groups. Relative strengths and quantity of different H-bonds were evaluated. Unlike erythritol, threitol contains o ver 5% of weak H-bonds. The formation from the melt of a crystalline racema te as a molecular compound of D- and L-forms is suggested. Comparisons with previous neutron scattering results are discussed. In solution, all four O H-groups of both tetritols form H-bonds of equal strength in accord with th e basicity of the solvent. (C) 1999 Elsevier Science Ltd. All rights reserv ed.