question_answer 81)

  How do you explain the presence of an aldehydic group in a glucose molecule ?

Answer:

                  Glucose reacts with hydroxylamine to form a monoxime and adds one molecule of hydrogen cyanide (HCN) to give a cyanohydrin. Therefore, glucose contains a carbonyl group which can be either an aldehyde or a ketone. On mild oxidation with , glucose gives a carboxylic acid, i.e., gluconic acid containing the same six carbon atoms as present in glucose. This indicates that the carbonyl group present in glucose is an aldehydic group and not a ketonic group. For structures ofoxime, cyanohydrin and gluconic acid, refer to sec. 14.2.4, pages 14/5-14/6.