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Long-range deuterium isotope effects on 13C chemical shifts of intramolecularly hydrogen-bonded compounds. Purpurogallins

✍ Scribed by Poul Erik Hansen

Publisher
John Wiley and Sons
Year
1993
Tongue
English
Weight
351 KB
Volume
31
Category
Article
ISSN
0749-1581

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✦ Synopsis

Abstract

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.

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