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17 O NMR spectra of the 1,6‐anhydro‐β‐ D ‐hexopyranoses and related‐compounds. Determination of configurational effects on the chemical shifts
Author(s) -
Lauterwein Jürgen,
Schulte Jürgen,
Schumacher Martin,
Černý Miloslav
Publication year - 1992
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260300408
Subject(s) - chemistry , chemical shift , steric effects , ether , nmr spectra database , stereochemistry , crystallography , reagent , spectral line , medicinal chemistry , organic chemistry , physics , astronomy
Well resolved natural‐abundance 17 O NMR spectra of the eight 1,6‐anhydro‐β‐D‐hexopyranoses and three deoxy model compounds were recorded in aqueous solution at 90°C. The assignment of the resonances was obtained by chemical shift comparison, O ‐acetylation, lanthanide shift reagents (Eu 3+ ) and, more generally applicable, by a computational search for the minimum of the sum of the squared deviations between the observed and calculated shifts. The 17 O chemical shifts were evaluated depending on the orientation of the hydroxyl groups, expressed in terms of additive γ‐ and δ‐interactions between the hydroxyl and ring ether groups. The γ‐ gauche effects were dominant in a range between −7 and −20 ppm. No appreciable effects have been detected of anti ‐periplanar hydroxyl groups on the 17 O chemical shifts. The syn ‐diaxial δ‐interaction was deshielding between hydroxyl groups, but shielding between a hydroxyl group and the bridge‐ether oxygen. A new type of interaction, a δ‐effect between equatorial hydroxyl oxygens in a planar zig‐zag arrangement, was detected. Arguments are presented suggesting that γ‐ gauche effects between oxygens are not related to steric compression.