Carbohydrate conformation

Carbohydrate conformation refers to the overall three-dimensional structure adopted by a carbohydrate (saccharide) molecule as a result of the through-bond and through-space physical forces it experiences arising from its molecular structure.

The physical forces that dictate the three-dimensional shapes of all molecules—here, of all monosaccharide, oligosaccharide, and polysaccharide molecules—are sometimes summarily captured by such terms as "steric interactions" and "stereoelectronic effects" (see below).

Saccharide and other chemical conformations can be reasonably shown using two-dimensional structure representations that follow set conventions; these capture for a trained viewer an understanding of the three-dimensional structure via structure drawings (see organic chemistry article, and "3D Representations" section in molecular geometry article); they are also represented by stereograms on the two dimensional page, and increasingly using 3D display technologies on computer monitors.

Chemical transformations and biological signalling mediated by conformation-dependent molecular recognition between molecules underlie all essential processes in living organisms.

In the pyranose system five conformers are possible: chair (C), boat (B), skew (S), half-chair (H) or envelope (E).

Conformations with 1,3-diaxial interactions are usually disfavored due to steric congestion and can shift equilibrium to the other chair form (example: 1C4 to 4C1).

However, since the substituent can be either axial or equatorial there are two types of exo-anomeric effects, one from axial glycosides and one from equatorial glycosides as long as the donating orbital is anti-periplanar to the accepting orbital.

The open chain form can close to give the pyranose and furanose with both the α- and β-anomers present for each.

The equilibrium population of conformers depends on their relative energies which can be determined to a rough approximation using steric and stereoelectronic arguments.