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Anomer
 
 
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In sugar
Sugar

Sugar is a class of edible crystalline substances, mainly sucrose, lactose, and fructose. Human taste buds interpret its flavor as sweet. Sugar as a basic food carbohydrate primarily comes from sugar cane and from sugar beet, but also appears in fruit, honey, sorghum, sugar maple , and in many other sources....
 chemistry
Chemistry

Chemistry is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions....
, an anomer is a special type of epimer
Epimer

In chemistry, epimers are diastereomers that differ in configuration of only one stereogenic center. Diastereomers are a class of stereoisomers that are non-superposable, non-mirror images of one another, unlike enantiomers which are non-superposable mirror images of one another....
. It is a stereoisomer (diastereomer
Diastereomer

Diastereomers are stereoisomers that are not enantiomers . Diastereomers can have different physical properties and different reactivity. In another definition diastereomers are pairs of isomers that have opposite configurations at one or more of the chiral centers but are not mirror images of each other ....
, more exactly) of a saccharide (in the cyclic form) that differs only in its configuration at the hemiacetal
Hemiacetal

Hemiacetals and hemiketals are compounds of the general formula R1R'1COR2, where R2 is not hydrogen....
 (or hemiketal) carbon, also called the anomeric carbon. If the structure is analogous to one with the hydroxyl group on the anomeric carbon in the axial position
Cyclohexane conformation

Cyclohexane conformation is a much studied topic in organic chemistry because of the complex interrelationship between the different conformational isomerisms of cyclohexane and its derivatives....
 of glucose, then the sugar is an alpha anomer. If, however, that hydroxyl is in the equatorial
Equatorial

Equatorial has different meanings:* In geography it relates to the equator of the Earth.* In meteorology, an Equatorial climate is the type of climate experienced near the equator....
 position, then the sugar is a beta anomer.






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In sugar
Sugar

Sugar is a class of edible crystalline substances, mainly sucrose, lactose, and fructose. Human taste buds interpret its flavor as sweet. Sugar as a basic food carbohydrate primarily comes from sugar cane and from sugar beet, but also appears in fruit, honey, sorghum, sugar maple , and in many other sources....
 chemistry
Chemistry

Chemistry is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions....
, an anomer is a special type of epimer
Epimer

In chemistry, epimers are diastereomers that differ in configuration of only one stereogenic center. Diastereomers are a class of stereoisomers that are non-superposable, non-mirror images of one another, unlike enantiomers which are non-superposable mirror images of one another....
. It is a stereoisomer (diastereomer
Diastereomer

Diastereomers are stereoisomers that are not enantiomers . Diastereomers can have different physical properties and different reactivity. In another definition diastereomers are pairs of isomers that have opposite configurations at one or more of the chiral centers but are not mirror images of each other ....
, more exactly) of a saccharide (in the cyclic form) that differs only in its configuration at the hemiacetal
Hemiacetal

Hemiacetals and hemiketals are compounds of the general formula R1R'1COR2, where R2 is not hydrogen....
 (or hemiketal) carbon, also called the anomeric carbon. If the structure is analogous to one with the hydroxyl group on the anomeric carbon in the axial position
Cyclohexane conformation

Cyclohexane conformation is a much studied topic in organic chemistry because of the complex interrelationship between the different conformational isomerisms of cyclohexane and its derivatives....
 of glucose, then the sugar is an alpha anomer. If, however, that hydroxyl is in the equatorial
Equatorial

Equatorial has different meanings:* In geography it relates to the equator of the Earth.* In meteorology, an Equatorial climate is the type of climate experienced near the equator....
 position, then the sugar is a beta anomer. For example, a-D-glucopyranose and ß-D-glucopyranose, the two cyclic forms of glucose
Glucose

Glucose , a monosaccharide also known as grape sugar, blood sugar, or corn sugar, is a very important carbohydrate in biology....
, are anomers. For -L- the a and ß are contrarywise. (see Glycosidic bond
Glycosidic bond

In chemistry, a glycosidic bond is a certain type of functional group that joins a carbohydrate molecule to another, which may be another carbohydrate....
 for details)

Glucoseab
The anomeric effect
Anomeric effect

In organic chemistry, the anomeric effect or Edward-Lemieux effect is a stereoelectronic effect that describes the tendency of heteroatomic substituents adjacent to a heteroatom within a cyclohexane ring to prefer the axial orientation instead of the less hindered equatorial orientation that would be expected from steric effects...
 helps stabilize the a-anomer. The term for interconversion between the two anomers is mutarotation
Mutarotation

'Mutarotation is the term given to the change in the specific rotation of a cyclic monosaccharide as it reaches an equilibrium between its α and β anomeric forms....
.

The two different anomers are two distinct chemical structures, and thus have different physical and chemical properties, notably optical rotation
Optical rotation

Optical rotation is the rotation of Linear polarization light as it travels through certain materials. It occurs in solutions of chirality molecules such as sucrose , solids with rotated crystal planes such as quartz, and Spin polarization gases of atoms or molecules....
. For example, a-D-glucose
Glucose

Glucose , a monosaccharide also known as grape sugar, blood sugar, or corn sugar, is a very important carbohydrate in biology....
 has an optical rotation of +112 degrees and its anomer, ß-D-glucose, has an optical rotation of +19 degrees.

Anomerization is the interconversion between the alpha and beta anomers.

See also

  • Haworth projection
    Haworth projection

    A Haworth projection is a common way of representing the cyclic Structural formula of monosaccharides with a simple three-dimensional perspective....


External links

  • On the Assignment of Anomeric Configuration (pdf)