In the Classroom
A Very Simple Method for Converting Haworth Representation to Zigzag Representation Janine Cossy* and Véronique Bellosta Laboratoire de Chimie Organique, Associé au CNRS, ESPCI, 10 Rue Vauquelin 75231, Paris Cedex 05, France
Monosaccharides generally exist in cyclic forms that are in equilibrium through the corresponding open-chain structures (1). Transforming the open chain into the corresponding Haworth structure (2), or the Fischer projection (3) or the Haworth structure into a zigzag representation is a frequent difficulty for undergraduate students taking a basic organic chemistry course. Here, we would like to present a very simple method to achieve the conversion of a Haworth representation to a zigzag representation. In the Haworth representation of aldohexoses and aldopentoses, the anomeric carbon is numbered 1 and the carbon of the hydroxymethyl is numbered 6 for hexoses and 5 for pentoses:
Examples
In converting a Haworth representation to a zigzag representation, one has to draw two parallel lines. The oddnumbered carbons are situated on the top line and the even-numbered carbons are situated on the bottom line. Carbon C-1 is situated on the right-hand side and on the top line:
The hydroxy groups are represented as follows: OH on
Haworth
Zigzag
odd carbon†
below the "plane"
above the "plane"
even carbon†
below the "plane"
below the "plane"
odd carbon††
above the "plane"
below the "plane"
even carbon††
above the "plane"
above the "plane"
In the particular case of Cn–Oring bond, if the CH2OH moiety is above the “plane’’ († ), the C5 – Oring bond (for hexoses) and the C 4 – Oring bond (for pentoses) have to be considered below the “plane’’. If the CH 2OH moiety is below the “plane’’ (††), the C 5 – Oring bond (for hexoses) and the C4 –Oring bond (for pentoses) have to be considered above the “plane’’. The same protocol can be applied to ketoses and to the open-chain portion of reducing disaccharides such as lactose or maltose, as the open chain portion of these disaccharides is an aldohexose unit. *Corresponding author.
Literature Cited 1. Ferrier, R. J.; Collins, P. M. Monosaccharide Chemistry, 1st ed.; Penguin: Harmondsworth, England, 1972; Chapter 2. 2. Wheeler, D. M. S.; Wheeler, M. M.; Wheeler, T. S. J. Chem. Educ. 1982, 59, 969. 3. Signorella, S.; Sala, L. F. J. Chem. Educ. 1991, 68, 105.
JChemEd.chem.wisc.edu • Vol. 75 No. 10 October 1998 • Journal of Chemical Education
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