Intramolecular, negatively charged, easily polarizable hydrogen bonds in monosalts of diols. Infrared and nuclear magnetic resonance studies

Abstract

Monotetraethylammonium salt solutions of o-bis(hydroxymethyl)benzene (compound 1), of 2,5-dimethylhexane-2,5-diol (compound 2), of 2,4-dimethyl-pentane-2,4-diol (compound 3), and of 2,3-dimethylbutane-2,3-diol (compound 4) were studied by n.m.r. and i.r. spectroscopies. In the mono salts, intramolecular OH…O^–⇌^–O…HO hydrogen bonds are formed quantitatively. Very intense continua in the i.r. spectra demonstrate that these hydrogen bonds are easily polarizable. With compounds 1 and 2 these continua extend from 3000 cm^–1 over the whole region studied. Comparison with theory shows that these hydrogen bonds are of medium length, and that typical double-minimum proton potentials are present in these hydrogen bonds. This confirms the n.m.r. result that the proton is delocalized in these hydrogen bonds. In the series of compounds 2–4, owing to sterical conditions, these intramolecular hydrogen bonds become weaker, the intensity of the continua decreases a little, and at smaller wavenumbers it vanishes to a large extent.