SPECTROSCOPIC DETECTION OF FREE LONE-PAIR GROUPS OR TERMINAL METHANOL MOLECULES IN METHANOL SOLUTIONS

When basic aprotic solvents are added to methanol they become hydrogen bonded, and there is a consequent growth in non-bonded lone-pairs, (LP)free. Although corresponding non-bonded OH groups, (OH)free, have been detected for alcohols and for water, using overtone infrared spectroscopy, no different spectroscopic evidence for (LP)free groups has previously been reported. We have found that unique OH stretching bands develop when strongly basic solvents such as dimethylsulphoxide are added to methanol. Band maxima assigned to (LP)free groups occur at 3440 cm-1 in the fundamental and 6790 cm-1 in the overtone region. These are at considerably higher frequencies than those for bulk methanol (3340 cm-1 and 6600 cm-1) showing that the hydrogen bond is weakened in this unit, as expected. Proton resonance shifts for the OH protons of methanol on adding basic aprotic cosolvents are reported, and explained in terms of these results. © 1979.