Abstract
Proton magnetic resonance and its simulation studies were performed on diacetyldehydroascorbic acid dimer and 5,6-diacetylascorbic acid. Even though great care was paid on the compas work to measure the chemical shifts and coupling constants of the compounds, some deviations were found between the observed NMR constants and the simulated values which gave spectrum similar to the observed lines. And it was concluded that a simulation procedure was indispensable to get NMR constants which fit to a theoretical treatment. The present work elucidated that the hindrance of free rotation of the carbon atoms of 5 and 6 position of 5,6-diacetylascorbic acid by neighbouring acetyl groups caused to give different vicinal coupling constants (5.45 and 9.00 Hz respectively), and the values of diacetyl dehydroascorbic acid dimer were almost similar (6.25 and 6.00 Hz, respectively), although ⊿■ of the geminal protons of the 6 position were nearly 2.5 times larger than that of 5,6-diacetylascorbic acid. The signs of the vicinal and geminal coupling constants were determined.
