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Encyclopedia of Physical Science and Technology EN002C-80 May 25, 2001 20:18

Carbohydrates 401

SCHEME 22 Elucidation of the structure of melibiose.

purity in order to prevent misleading results caused by angle between H-1 and H-2 in the disaccharide. Since this
contaminants. angle depends not only on the anomeric configuration,
but also on the ring conformation, both are determined
concurrently. The sample is irradiated at the frequency
6. Conformation
of the H-1, so that the signal of H-2 is identified (since
a. By NMR spectroscopy. The most common it is decoupled partly), and J 2,3 determined. The proce-
method for determining both the anomeric configuration dure is repeated by irradiating the sample at the frequency
and the ring conformation of oligosaccharides is NMR of the H-2 absorption (to identify the signal due to H-3
spectroscopy. The coupling constant of the anomeric pro- and measure J 3,4 ) and then at the frequency of H-3 to
ton (J 1,2 ) is measured and used to determine the dihedral identify the signal due to H-4 and so on. When all the