Question

The reaction of glucose with hydrogen cyanide confirms the ______

(a) straight chain structure of glucose

(b) presence of a carbonyl group in glucose

(c) presence of an aldehyde group in glucose

(d) presence of a keto group in glucose

The question was asked in an internship interview.

My enquiry is from Biomolecules Carbohydrates topic in chapter Biomolecules of Chemistry – Class 12

Answer 1

Right choice is (b) presence of a carbonyl group in glucose

To elaborate: Glucose reacts with hydrogen cyanide to form glucose cyanohydrin, where the carbonyl double bond gets cleaved to form one C-OH bond and one C-CN bond. This indicates the presence of a carbonyl group but does not confirm whether it is an aldehydic or a keto group.