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MCQMediumJEE 2023Aldehydes & Ketones

JEE Chemistry 2023 Question with Solution

Cyclohexylamine when treated with nitrous acid yields (P). On treating (P) with PCC results in (Q). When (Q) is heated with dilute NaOH, we get (R). The final product (R) is:

Four product structures labeled 1 to 4 showing cyclohexanone-derived compounds for identifying the final reaction product.
  • A

    Option (1)

  • B

    Option (2)

  • C

    Option (3)

  • D

    Option (4)

Answer

Correct answer:B

Step-by-step solution

Standard Method

Given: Cyclohexylamine is treated successively with nitrous acid, PCC, and dilute NaOH on heating.

Find: The final product (R).

Cyclohexylamine reacts with nitrous acid to give the corresponding alcohol (P). Oxidation of this alcohol with PCC gives the ketone (Q).

Reaction scheme showing cyclohexylamine converted to cyclohexanol with HNO2, then oxidized by PCC and finally treated with concentrated sodium hydroxide and heat to give the final conjugated ketone product.

On heating (Q) with dilute NaOH, condensation occurs to form the cyclohexene derivative shown in option (2).

Therefore, the correct option is B.

Extracted Explanation

Given: Cyclohexylamine (C6H11NH2)\left(\text{C}_6\text{H}_{11}\text{NH}_2\right) reacts with nitrous acid.

Find: Which structure corresponds to the final product (R).

Cyclohexylamine (C6H11NH2)\left(\text{C}_6\text{H}_{11}\text{NH}_2\right) reacts with nitrous acid (HNO2)\left(\text{HNO}_2\right) to form (P). On treating this with PCC (Pyridinium chlorochromate), oxidation occurs to form a ketone (Q). When (Q) is heated with dilute NaOH, it undergoes a condensation reaction forming a cyclohexene derivative (R). Thus, the final product (R) is the structure shown in option (2).

Therefore, the correct option is B.

Common mistakes

  • Assuming nitrous acid forms a stable diazonium salt here is incorrect because a primary aliphatic amine typically gives the corresponding alcohol. Convert cyclohexylamine first to cyclohexanol, not to an isolable diazonium product.

  • Treating PCC as if it gives an alkene directly is wrong. PCC oxidizes the alcohol intermediate to the ketone (Q), which then undergoes base-induced condensation on heating.

  • Choosing a saturated ketone product misses the effect of heating with NaOH. Under these conditions, condensation gives a more conjugated unsaturated product, so look for the alkene-containing structure.

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