Question

Which of the following represents the C-4 epimer of L-glucose?

(A)

(B)

(C)

(D)

Answer 1

Hint: To answer this question, start by drawing the structure of L-glucose. You should know that epimers are diastereomers that differ from each other at one chiral centre. Number the carbon atoms in the L-glucose and find the C-4 carbon and then draw its epimer to find the correct answer.

Complete step by step solution:
We know that glucose is basically a sugar which is a carbohydrate and its structure is-

To answer the given question, firstly let us discuss what epimer and L-glucose is. In organic chemistry, we identify the stereoisomers by finding out the absolute configuration i.e. R or S for the chiral centres in a molecule. An epimer is basically a diastereomer which has at least two chiral centres but are different from each other in absolute configuration at one centre only. We generally find epimers for carbohydrate chains like glucose, galactose etc. Now let’s discuss L-glucose.
We know that mirror images of each other are known as enantiomers. One of the enantiomers is designated as the L-enantiomer and the other as R-enantiomer. When we pass a plane of polarised light through a compound, the isomer which rotated the plane of polarised light towards right, or clockwise direction is known as the Dextro (D) isomer and the isomer which rotates the plane of polarised light in the anti-clockwise direction or towards left side is known as the Levo (L) isomer. Now let us draw the structure of L-glucose.

Now we have to find the C-4 epimer i.e. the configuration at C-4 will be different i.e. H and OH are simply interconverted. Therefore, the C-4 epimer of L-glucose is-

Therefore, the correct answer is option [C]

Note: The isomers which are mirror images of each other are known as enantiomers. We generally found enantiomers of compounds having a chiral centre and are asymmetric. The mirror images are non-superimposable. The stereoisomers which are not mirror images of each other are diastereomers. They are neither superimposable non mirror images of each other. Generally, compounds having two or more stereo-centres are diastereomers.