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MCQMediumJEE 2026Reaction Mechanisms (Substitution, Addition, Elimination)

JEE Chemistry 2026 Question with Solution

Given below are two statements:

Statement I: The dipole moment of R–CNR\text{–}CN is greater than R–NCR\text{–}NC and R–NCR\text{–}NC can undergo hydrolysis under acidic medium to produce R–COOHR\text{–}COOH.

Statement II: R–CNR\text{–}CN hydrolyses under acidic medium to produce a compound which on treatment with SOCl2SOCl_2, followed by the addition of NH3NH_3 gives another compound (X)(X). This compound (X)(X) on treatment with NaOCl/NaOHNaOCl/NaOH gives a product, that on treatment with CHCl3/KOH/ΔCHCl_3/KOH/\Delta produces R–NCR\text{–}NC.

In the light of the above statements, choose the correct answer from the options given below.

  • A

    Both Statement I and Statement II are true

  • B

    Both Statement I and Statement II are false

  • C

    Statement I is true but Statement II is false

  • D

    Statement I is false but Statement II is true

Answer

Correct answer:D

Step-by-step solution

Standard Method

Given: Two statements about hydrolysis of R–CNR\text{–}CN and R–NCR\text{–}NC, and a reaction sequence involving SOCl2SOCl_2, NH3NH_3, NaOCl/NaOHNaOCl/NaOH and CHCl3/KOH/ΔCHCl_3/KOH/\Delta.

Find: Which statement is true.

For Statement I, although the dipole moment of R–CNR\text{–}CN is greater than that of R–NCR\text{–}NC, the statement is incorrect in saying that R–NCR\text{–}NC undergoes acidic hydrolysis to form R–COOHR\text{–}COOH. In reality, nitriles R–CNR\text{–}CN undergo acidic hydrolysis to give carboxylic acids, whereas isocyanides R–NCR\text{–}NC do not give R–COOHR\text{–}COOH in this way. Therefore, Statement I is false.

For Statement II, the sequence given is correct:

R–CN→acidic hydrolysisR–COOHR\text{–}CN \xrightarrow[\text{acidic hydrolysis}]{} R\text{–}COOH R–COOH→SOCl2R–COClR\text{–}COOH \xrightarrow{SOCl_2} R\text{–}COCl R–COCl→NH3R–CONH2 (X)R\text{–}COCl \xrightarrow{NH_3} R\text{–}CONH_2 \,(X) R–CONH2→NaOCl/NaOHR–NH2R\text{–}CONH_2 \xrightarrow{NaOCl/NaOH} R\text{–}NH_2 R–NH2→CHCl3/KOH/ΔR–NCR\text{–}NH_2 \xrightarrow{CHCl_3/KOH/\Delta} R\text{–}NC

The last step is the carbylamine reaction, so Statement II is true.

Therefore, Statement I is false and Statement II is true. The correct option is D.

Reaction Sequence Check

Given: A comparison of nitriles and isocyanides, and a multistep conversion starting from R–CNR\text{–}CN.

Find: Whether each statement is true or false.

  1. Check the hydrolysis part first.
  • Nitrile R–CNR\text{–}CN on acidic hydrolysis gives carboxylic acid R–COOHR\text{–}COOH.
  • So the claim that R–NCR\text{–}NC gives R–COOHR\text{–}COOH is incorrect.
  1. Now verify the second statement step by step.
  • Acidic hydrolysis:
R–CN→R–COOHR\text{–}CN \rightarrow R\text{–}COOH
  • Conversion of acid to acid chloride:
R–COOH→SOCl2R–COClR\text{–}COOH \xrightarrow{SOCl_2} R\text{–}COCl
  • Reaction with ammonia to form amide:
R–COCl→NH3R–CONH2R\text{–}COCl \xrightarrow{NH_3} R\text{–}CONH_2
  • Hofmann degradation:
R–CONH2→NaOCl/NaOHR–NH2R\text{–}CONH_2 \xrightarrow{NaOCl/NaOH} R\text{–}NH_2
  • Carbylamine reaction:
R–NH2→CHCl3/KOH/ΔR–NCR\text{–}NH_2 \xrightarrow{CHCl_3/KOH/\Delta} R\text{–}NC
  1. Hence the full sequence is chemically valid, so Statement II is true.

Therefore, the correct option is D.

Common mistakes

  • Confusing nitriles R–CNR\text{–}CN with isocyanides R–NCR\text{–}NC. This is wrong because their connectivity and reactions are different. Check which atom of the –C ⁣N\text{–}C\!N unit is attached to RR before deciding the hydrolysis product.

  • Assuming that both R–CNR\text{–}CN and R–NCR\text{–}NC give R–COOHR\text{–}COOH on acidic hydrolysis. This is wrong because the standard acidic hydrolysis to carboxylic acid applies to nitriles, not the isocyanide statement given here. Identify the functional group first, then apply the reaction.

  • Missing that R–CONH2R\text{–}CONH_2 undergoes Hofmann degradation with NaOCl/NaOHNaOCl/NaOH to form R–NH2R\text{–}NH_2. Without this step, the final formation of R–NCR\text{–}NC cannot be justified. Track each intermediate carefully.

  • Forgetting that the reaction of a primary amine with CHCl3/KOH/ΔCHCl_3/KOH/\Delta is the carbylamine reaction. This is wrong because that named reaction is the key step producing R–NCR\text{–}NC. Recognize the reagent pattern to identify the product.

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