Exams › JEE Main › Chemistry

Which of the following compounds is an example of a conjugated diketone (the two C=O groups in conjugation through the pi system)?

1. CH3-C(=O)-CH2-CH2-CH2-C(=O)-CH3
2. CH3-C(=O)-CH2-(cyclohexane ring)-C(=O)
3. A benzene ring bearing two carbonyl groups at the para positions
4. A benzene ring attached to C(=O)-CH2-CH2-C(=O)-CH3

Correct answer: A benzene ring bearing two carbonyl groups at the para positions

Solution

In the para-diacylbenzene (e.g. terephthalaldehyde / p-diketone), both C=O groups are directly bonded to the benzene ring, so the carbonyl pi systems are conjugated through the aromatic ring. The other options have sp3 CH2 spacers that break conjugation.

Related JEE Main Chemistry questions

• What is the product formed when toluene (C6H5CH3) is treated with chromyl chloride (CrO2Cl2)?
• o-Xylene is first treated with HNO3 to give compound X, which on reaction with phenol in the presence of H2SO4 forms product Y. What is Y?
• What products are formed when a benzene ring containing a formyl group (–CHO) and a chloro substituent is treated with 50% KOH?
• Which of the following compounds contains a carboxyl group (–COOH)?
• Which of the following compounds is converted to the corresponding hydrocarbon on reduction with zinc and hydrochloric acid?
• Why do carboxylic acids not undergo the typical addition–elimination reactions shown by aldehydes and ketones?

⚔️ Practice JEE Main Chemistry free + battle 1v1 →