ring have distinct effects on its conformational preference. There are also conformational and stereochemical effects specific to the pyranose ring. Nomenclature To name conformations of pyranose, first the conformer is determined. The common conformers are similar to those found in cyclohexane, and these form the basis of the name. Common conformations are chair (C), boat (B), skew (S), half-chair (H) or envelope (E). The ring atoms are then numbered; the anomeric, or hemiacetal, carbon is always 1. Oxygen atoms in the structure are, in general, referred to by the carbon atom they are attached to in the acyclic form, and designated O. Then: Position the ring so that, if looking at the top face, the atoms are numbered clockwise. In the chair and skew conformations, the reference plane should be selected. In the chair conformation, the reference plane is chosen such that the lowest-numbered atom (usually C-1) is exoplanar. In the skew conformation, the plane contains three adjacent atoms and one other with the atom with the lowest possible number exoplanar. Atoms above the plane are written before the conformer label, as a superscript Atoms below the plane are written following the conformer label, as a subscript NMR spectroscopy As shown by the relative structure energies in the diagram above, the chair structures are the most stable carbohydrate form. This relatively defined and stable conformation means that the hydrogen atoms of the pyranose ring are held at relatively constant angles to one another. Carbohydrate NMR takes advantage of these dihedral angles to determine the configuration of each of the hydroxyl groups around the ring. See also Furanose Mutarotation Monosaccharide Carbohydrate conformation References Carbohydrate chemistry