H2O, HDO, and CH3OH Infrared Spectra and Correlation with Solvent Basicity and Hydrogen Bonding

Abstract

A study has been made of the infrared O—H bands for CH₃OH, DOH, and H₂O in solution and of their correlation with hydrogen bonding and solvent basicity. Infrared bands for the three fundamentals and the first bending overtone of H₂O and for the O—H stretching fundamentals of DOH and CH₃OH have been measured between 30 and −40 °C in a solvent range extending from weakly interacting fluorocarbons to strongly hydrogen-bonding organic amines. The O—H stretching bands for the weakly acidic solutes CH₃OH, DOH, and H₂O are mostly Lorentzian in shape and move to lower frequencies with higher extinctions in the more basic solvents. Many correlations are found between the stretching frequencies and band areas, and between the frequencies and solvent basicity. Monofunctional CH₃OH is found to be a stronger acid and forms stronger hydrogen-bonds with a given base than do the doubly bonded DOH and HOH which show equal dibasic acid strengths.The wide, overlapped, fundamental stretching bands for H₂O strongly hydrogen-bonded to the tertiary amines and for ice have been partially resolved and unequivocally assigned, showing that there is no cross-over of the ν ₃ and ν₁ bands despite the strong hydrogen-bonding.At higher temperatures in solvents containing both hydrophobic and strongly basic groups water was found with the lower C_s type symmetry, in which unbonded O—H groups gave sharp bands in the 3680–3650 cm⁻¹ region in addition to the wide hydrogen-bonded bands at lower frequencies.