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Difference between revisions of "Anomeric centre (alpha and beta)"
(Created page with ' * Author: Stephen Withers * Responsible Curator: Spencer Williams ---- The '''anomeric''' centre of a sugar is a stereocentr…') |
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* [[Author]]: [[User:Withers|Stephen Withers]] | * [[Author]]: [[User:Withers|Stephen Withers]] | ||
* [[Responsible Curator]]: [[User:SpencerWilliams|Spencer Williams]] | * [[Responsible Curator]]: [[User:SpencerWilliams|Spencer Williams]] | ||
---- | ---- | ||
| − | The '''anomeric''' | + | The '''anomeric centre''' of a sugar is a stereocentre created from the intramolecular formation of an acetal (or ketal) of a sugar hydroxyl group and an aldehyde (or ketone) group. The two stereoisomers formed from the two possible stereochemistries at the anomeric centre are called anomers. They are diastereoisomers of one another. |
| − | The configuration at the anomeric centre ( | + | The configuration at the anomeric centre (that derived from the carbonyl carbon) is denoted alpha- (α-) or beta- (β-) by reference to the stereocentre that determines the absolute configuration. In a Fischer projection, if the substituent off the anomeric centre is on the same side as the oxygen of the configurational (D- or L-) carbon, then it is the α--anomer. If it is directed in the opposite direction it is the β-anomer. |
| − | + | [[File:Alphabeta arabinose.png|center|700px]] | |
| + | <center>'''Example 1. Fischer projections and Haworth conformational projections of L-arabinose.</center> | ||
| + | <br> | ||
| − | + | [[File:alpha&beta_fructose.png|center|1000px]] | |
| + | <center>'''Example 2. Fischer projections and Haworth conformational projections of D-fructose.'''</center> | ||
| + | |||
| + | In the case of D-hexopyranoses drawn in the 'usual' Haworth projection, the α-D-anomer is the isomer with the anomeric substituent on the opposite face to the C5 (hydroxymethyl) substitutent, ie directed ‘down’; the β-D-anomer is that with the anomeric substituent being on the same face as the C5 hydroxymethyl substitutent, ie directed up. For L-hexoses the α-L-anomer has the anomeric group pointing up; the β-L-anomer has this group pointing down. | ||
| + | |||
| + | [[File:alpha&beta_glucose.png|center|700px]] | ||
| + | <center>'''Example 3. Fischer projections and Haworth conformational projections of D-glucose.'''</center> | ||
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==References== | ==References== | ||
| − | # | + | <biblio> |
| − | + | #StickWilliams2009 isbn=9780240521183 | |
| + | </biblio> | ||
[[Category:Definitions and explanations]] | [[Category:Definitions and explanations]] | ||
Latest revision as of 10:19, 7 November 2014
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The anomeric centre of a sugar is a stereocentre created from the intramolecular formation of an acetal (or ketal) of a sugar hydroxyl group and an aldehyde (or ketone) group. The two stereoisomers formed from the two possible stereochemistries at the anomeric centre are called anomers. They are diastereoisomers of one another.
The configuration at the anomeric centre (that derived from the carbonyl carbon) is denoted alpha- (α-) or beta- (β-) by reference to the stereocentre that determines the absolute configuration. In a Fischer projection, if the substituent off the anomeric centre is on the same side as the oxygen of the configurational (D- or L-) carbon, then it is the α--anomer. If it is directed in the opposite direction it is the β-anomer.
In the case of D-hexopyranoses drawn in the 'usual' Haworth projection, the α-D-anomer is the isomer with the anomeric substituent on the opposite face to the C5 (hydroxymethyl) substitutent, ie directed ‘down’; the β-D-anomer is that with the anomeric substituent being on the same face as the C5 hydroxymethyl substitutent, ie directed up. For L-hexoses the α-L-anomer has the anomeric group pointing up; the β-L-anomer has this group pointing down.
References
- Robert V. Stick and Spencer J. Williams. (2009) Carbohydrates. Elsevier Science.