Carbohydrates, conformational energetics

It is very probable that the energetics favoring the left-handed helix are also effective when the molecule is in solution. These forces, therefore, would also affect the contribution of chain stiffness and form to the optical rotation. The relation between these two phenomena and the conformation revealed by x-rays remains to be explored. A preliminary attempt at relating the conformation of /3-d-(l— 4)-linked polysaccharides to simple conformational concepts in carbohydrate chemistry has focused on the carbon-oxygen bond sequence between the residues (see Fig. 22) that form the well-known molecule methylal. Measurements of dipole moments of methylal show that the conformation shown in Fig. 22A is favored here, the group moments are in partial opposition, and the O-C-4 bond is gauche, relative to C-1-0-5. This is exactly the con-... 

The historic development of the understanding of carbohydrate stereochemistry has been briefly reviewed, and a lecture with four references on the energetics and geometry of furanoid tems has been published. Two complementary descriptions of the conformational behaviour of furanose rings have been presented (i) quantum-mechanical energy calculations and (ii) by a geometrical model of pseudorotation in five-membered rings. ... 

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