Question

Structure of D mannose is as shown.

Structure of L mannose will be:
(A)

(B)

(C)

(D)

Answer 1

Hint: We know that consider the number of carbon atoms found in L-mannose and also all of the options given here. Also consider the nature of the given options as aldoses or ketoses. Structures are a specific type of stereoisomer that has multiple stereocenters but only differs from one another by the configuration at one of the stereogenic centers.

Complete step by step solution:
By stereogenic center, we mean, the carbon atom that has four different atoms or groups of atoms bonded to it. The molecular formula and the functional groups found in Structures is the same. We know that D-fructose is a ketose (having ketone group) sugar while L-mannose, D-glucose, as well as D-galactose are all aldose (having aldehyde group) sugars. Thus, we can directly rule out D-fructose as one of our answers. In this case, we need to examine the structure of all the mentioned options to the structure of L-Mannose. The structure of L-mannose is:

The D and L-mannose are enantiomers and thus will be a mirror image of each other. Thus the structure of L-mannose will be the mirror image of D-mannose.
Hence the correct answer is (C).

Additional Information:
Here, we can see the aldose group at the leftmost end of the molecule. Compare the structure of this molecule with the structure of L-mannose, you will see that the position of the hydroxyl group differs in two places. The second and the fourth carbons have hydroxyl groups that are in different positions than L-mannose. From this, we see that in D-glucose and L-mannose, one of the stereocenters has a different stereochemistry. So according to the definitions L-mannose can be the epimer of only D-glucose.

Note:
Remember that we should know that Mannose is a $C-2$ epimer of glucose and a sugar molecule of the aldohexose series of carbohydrates. D-galactose is also a carbohydrate of the aldohexose series of carbohydrates but it is a $C-4$ epimer of glucose. Mannose is important in human metabolism, particularly in the proper glycosylation of native proteins.