Disaccharides conformational equilibria

Disaccharide conformations are determined by their free energies, rather that just their mechanical potential energies, and as in the cases of trehalose and neocarrabiose, the solvent can affect the free energy surface governing conformational equilibrium. A more useful description of disaccharide energetics would be a Ramachandran conformational potential of mean force (pmf) which included not only entropic effects but also the influence of the solvent. 

D-(+)-galactose (15) is an example of the consecutive numbering of the carbon ring atoms in a monosaccharide (disaccharide see p. 253). Carbohydrates can exist in a cyclic and an acyclic structure. For this reason there is a special position in the structure of a monosaccharide, the carbon atom C-l and so called anomeric center. You can see that there is an equilibrium between er-anomer a-15 and / -anomer /3-15 of D-(+)-glucopyranose over the acyclic aldehyde structure 16. Both are cyclic hemi-acetals. The /Tanomer is the preferred conformation, but there are a few effects, like sterical or stereoelectronical effects (anomeric effect, inverse anomeric effect), which have influence on the a /i rate. 

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