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Can anyone explain to me how to identify epimers and anomers in carbohydrates (sugars)? Also, state examples.

1 Answer
Jul 21, 2015

Answer:

Epimers and anomers are both optical isomers that differ in the configuration at a single carbon atom, but there is a difference in their definitions.

Explanation:

Epimers

Epimers are optical isomers that differ in the configuration of a single carbon atom

For example, D-galactose and D-mannose are epimers of D-glucose.

biochemnoob.files.wordpress.com
(from biochemnoob.wordpress.com)

D-Galactose is an epimer of D-glucose because the two sugars differ only in the configuration at #"C-4"#.

D-Mannose is an epimer of D-glucose because the two sugars differ only in the configuration at #"C-2"#.

Anomers

When a molecule such as glucose converts to a cyclic form, it generates a new chiral centre at #"C-1"#.

www.chem.ucalgary.ca
(from www.chem.ucalgary.ca)

The carbon atom that generates the new chiral centre (#"C-1"#) is called the anomeric carbon.

Anomers are special cases — they are epimers that differ in configuration only at the anomeric carbon.

For example, α-D-glucose and β-D-glucose are anomers.

wikispaces.psu.edu
(from wikispaces.psu.edu)

The α form has the anomeric #"OH"# group at #"C-1"# on the opposite side of the ring from the #"CH"_2"OH"# group at #"C-5"#.

The β form has the anomeric #"OH"# group on the same side as the #"CH"_2"OH"#.

In D-fructose, the carbonyl group is at #"C-2"#.

web.pdx.edu
(fromweb.pdx.edu)

Here, #"C-2"# is the anomeric carbon.

Fructose
(From pinterest.com)

α-D-Fructofuranose and β-D-fructofuranose are anomers.