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20.4: Conventions for Indicating Ring Size and Anomer Configurations of Monosaccharides

  • Page ID
    22303
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    The oxide ring is six-membered in some sugars and five-membered in others, and it is helpful to use names that indicate the ring size. The five- and six-membered oxide rings bear a formal relationship to oxa-2,5-cyclohexadiene and oxa-2,4-cyclopentadiene that commonly are known as pyran and furan, respectively:

    Roberts and Caserio Screenshot 20-3-1.png
    Figures 20-1 and 20-2).

    There is an important question as to which one of the two anomeric forms of a sugar should be designated as \(\alpha\) and which one as \(\beta\). The convention is simple; the \(\alpha\) anomer is the one that has the same configuration of the \(\ce{OH}\) at the anomeric carbon as the carbon which determines the configuration of the sugar itself:

    Roberts and Caserio Screenshot 20-3-2.png

    Contributors and Attributions

    John D. Robert and Marjorie C. Caserio (1977) Basic Principles of Organic Chemistry, second edition. W. A. Benjamin, Inc. , Menlo Park, CA. ISBN 0-8053-8329-8. This content is copyrighted under the following conditions, "You are granted permission for individual, educational, research and non-commercial reproduction, distribution, display and performance of this work in any format."