Question 27: [Organic > Carbonyl Compounds]:
Burnt sugar has a characteristic smell caused partly by the following compound. It has two functional groups indicated by Q and R.
When this compound is tested in a laboratory with 2,4-dinitrophenylhydrazine and Fehling’s reagent, which functional groups are responsible for positive tests?
| | 2,4-dinitrophenylhydrazine | Fehling’s reagent |
| A | Q and R | Q and R |
| B | R only | Q and R |
| C | Q and R | R only |
| D | Q only | R only |
Reference: Past Exam Paper – November 2002 Paper 1 Q27
Solution 27:
Answer: C.
Both carbonyl groups will react with 2,4 DNPH due to the presence of the C=O bond. Thus options B and D are eliminated.
Fehling’s reagent is a solution which reacts only with the aldehyde group, the CHO.
Thus option A is eliminated leaving C as the correct answer.
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