✍ Scribed by Takashi Yoshida; Tsutomu Hatano; Takuo Okuda
No coin nor oath required. For personal study only.
The structures of hydrolysable tannins, each existing as an equilibrium mixture due to tautomerization at the sugar core(s) or at the dehydrohexahydroxydiphenoyl group (five‐ and six‐membered hemiacetal forms) in the molecule, were elucidated by NMR, employing 2D NMR techniques (COSY, NOESY, ^1^H^13^C long‐range COSY, etc.), on derivatives which avoid the spectral complication due to equilibration.
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6-Azidopurine nucleoside labeled with 15 N at N-1 position was synthesized. 15 N NMR spectra, 15 N-1 H and 15 N-13 C coupling constants were measured. Two well-separated sets of signals for two tautomeric forms were detected.
The =C chemical shifts of the four isomeric ring forms of D-digitoxose in dimethyl sulfoxide-d, solution have been assigned completely by DEPT 13C NMR spectrum editing and two-dimensional carbon-proton chemical shift correlation spectroscopy. The =C chemical shifts are discussed in terms of their de