Which of the following are epimers a glucose and fructose bg

Which of the following are epimers?

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

Solution

Galactose and Mannose are different from each other in the stereochemistry of carbons 2 and 4. They are described as “Diastereoisomers”. They are not mirror images and differ widely in both physical and chemical properties.(2,4-epimers)

“Epimers” are diastereoisomers which differ in configuration of single asymmetric center adjacent to anomeric one (C=O)

A. Glucose and fructose is not a epimer.   

B. D glucose and D galactose are epimer which differ at C4.

C. D galactose and D mannose are Diastereoisomers of glucose but they are called as 2, 4 epimer

D. Lactose and maltose are not epimer