O-17 NMR-SPECTROSCOPY - MULTIPLE INTRAMOLECULAR HYDROGEN-BONDED PHENOLIC CARBONYL SYSTEMS

O-17 NMR spectra of dihydroxyanthraquinones 1-2 in toluene show two carbonyl signals, the upfield one of which is assigned to the intramolecular hydrogen-bonded C=O. The O-17 NMR data for dithranol (1,8-dihydroxyanthrone) 5 are consistent with the keto-tautomer. The contribution of hydrogen-bonding (DELTA-delta(HB)) to the chemical shifts of the intramolecular hydrogen-bonded carbonyl groups, after correction for electronic effects, was determined to be 94, 94 and 79 ppm, respectively, for 1, 2 and 5 in toluene. No evidence for measurable intermolecular hydrogen bonding was noted (DELTA-delta(Ref) = 0). The results for 1, 2 and 5 in toluene and that for 5 in acetonitrile support the presence of two strong, intramolecular hydrogen bonds to the same carbonyl group. The O-17 NMR data for 2,2'-dihydroxybenzophenone 6 as well as a series of model compounds were obtained in toluene and in acetonitrile. The results for 6 in toluene show the presence of intramolecular and intermolecular components. The DELTA-delta(Ref) value in toluene of 2 ppm was 20% of that for the presence of "free' phenolic group. The data for 6 in acetonitrile were consistent with only one intramolecular hydrogen bond to the carbonyl. For the mobile system 6 the O-17 NMR data were found to be solvent dependent and to contain intermolecular hydrogen-bonding components. In the rigid planar systems, the O-17 NMR data were consistent with double intramolecular hydrogen-bonding