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Conformational nomenclature

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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, 2]. 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 [3].

It should be noted that the conformational symbols for enantiomers are different. This is because the reference plane is the same, yet application of the left-hand rule results in a different 'top' and 'bottom' face. Thus the mirror image of α~D-glucose-4C1 is α-L-g1ucose-1C4. It is therefore important to state whether the D or L form is under consideration.

Conformations.png

References

  1. Conformational nomenclature for five- and six-membered ring forms of monosaccharides and their derivatives, Pure and Appl. Chem., 1981, 53, 1901—1905. DOI: 10.1351/pac198153101901
    [IUPACNomenclature1981]
  2. (1980) IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN). Conformational nomenclature for five and six-membered ring forms of monosaccharides and their derivatives: recommendations 1980. Eur J Biochem. 111, 295-8. PubMed ID:7460897 | HubMed [IUPACNomenclature1980]
  3. Stereochemistry of Carbohydrates, J. Fraser Stoddart, John Wiley & Sons Inc, 1971, 264 pages.
    [Stoddart1971]