Answer to Question #7181 in Organic Chemistry for saeed ahmad

Question

why glucose have different arrangment of the hydroxal group at C-3 then the other hydroxal group ?

Answer 1

The glucose molecule has an open as opposed to cyclic and unbranched backbone of six carbon atoms, C-1 through C-6; where C-1 is part of an aldehyde group H(C=O)-, and each of the other five carbons bears one hydroxyl group -OH. The remaining bonds of the backbone carbons are satisfied by hydrogen atoms -H.Each of the four carbons C-2 through C-5 is chiral, meaning that its four bonds connect to four different substituents. In D-glucose, these four parts must be in a specific three-dimensional arrangement. Namely, when the molecule is drawn in the Fischer projection, the hydroxyls on C-2, C-4, and C-5 must be on the right side, while that on C-3 must be on the left side.