Question

Which of the following are epimers?

a) glucose and fructose, b)glucose and galactose, c) galactose and mannose, OR d) lactose and maltose

Answer 1

Two sugars are called epimers that differ by stereochemistry at only a single carbon .

Out of the given options , glucose and galactose are epimers .

Explanation:

Galactose and glucose differ only at C4 carbon, thus galactose and glucose are epimers.

Fructose and glucose as well as maltose and lactose differ at more than one carbon, hence they are not epimers. Also, galactose and mannose are not epimers as they differ at two chiral carbons (C2 and C4).

Correct choice should be:

(b) Glucose and galactose

Note :

Mannose and glucose are also epimers.

D-	D-glucose	D-
СНО Но-С—н 3! Но - С- н Н-С-ОН Н-С-ОН 6, CH,OН D-mannose	'сно СНО H-C-OH 3! HO-C-H H-C-OH Н-с-оН 6. CH-ОН D-glucose	СНО H-C-OH 3 Но -с—н но-с— н 5! Н-с-ОН 6. CH,OH D-galactose