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Conformational nomenclature
The conformations adopted by a pyranose or furanose ring are denoted by a system in which a capital letter indicates the overall shape, C = chair, B = boat, H = half chair, S = skew boat, E = envelope [1]. The first four of these conformations has four atoms in a plane; the envelope conformation has five.
The particular conformation is then denoted by assigning the letter corresponding to the shape (C, B, H, S, E); determining the four (or five) atoms that define the plane; assigning a 'top' and 'bottom' face through the use of a left-hand rule counting in the order of increasing ring carbon; and then indicating the identities and relative positions (top face = superscript and prefix; bottom face = subscript and suffix) of the remaining two atoms on that capital letter. In the case of the envelope conformation, only a single atom is located outside of the plane. For a more detailed discussion see the excellent book by J. Fraser Stoddard [2].
References
- 1 Conformational nomenclature for five- and six-membered ring forms of monosaccharides and their derivatives, ure and Appl. Chem., 1981, 53, 1901—1905.
- 2 Stereochemistry of Carbohydrates, J. Fraser Stoddart, John Wiley & Sons Inc, 1971, 264 pages.