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Long‐range deuterium isotope effects on 13 C chemical shifts of intramolecularly hydrogen‐bonded compounds. Purpurogallins
Author(s) -
Hansen Poul Erik
Publication year - 1993
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.1260310115
Subject(s) - chemistry , deuterium , kinetic isotope effect , chemical shift , hydrogen , hydrogen bond , deuterium nmr , isotope , carbon 13 , carbon 13 nmr , stereochemistry , molecule , organic chemistry , physics , quantum mechanics
Long‐range deuterium isotope effects on 13 C chemical shifts, n ΔC(OD), were studied in the intramolecularly hydrogen‐bonded purpurogallins (benzotropolones). A very large long‐range isotope effect from the hydrogenbonded 4‐OH(D) is observed over six bonds at C‐7. Further, long‐range isotope effects are transmitted over as many as eight bonds. The transmission pathway including the carbonyl carbon is favoured, and some of the long‐range effects are transmitted via the carbonyl group. Large long‐range isotope effects are thus observed in hydrogen‐bonded systems with effective conjugation to the carbonyl group via alternating double bonds. This study indirectly supports recent theoretical predictions. The 13 C and 1 H NMR spectra of purpurogallin and its 2,3‐dimethyl, 2,3,6‐trimethyl and 2,3,4,6‐tetramethyl derivatives are assigned, and the hydrogen bond patterns are established based on the O H chemical shifts and 2 ΔC(OD) isotope effects.