Q.Explain following:

Showing the 12 most recent of 25 on this concept.

1. CBSE 2026Set ANNUAL1 mark
   Q.Write chemical equation for conversion from methylamine into methylisocyanide.

   ›Reveal solutionSolution

   Primary amines react with chloroform and alcoholic KOH to give a foul-smelling isocyanide - this is the carbylamine reaction, a test unique to primary amines.

   …

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2. CBSE 2026Set ANNUAL1 markMCQ
   Q.The reaction of ethylamine with chloroform in the alcoholic KOH gives:

   (a) C2H5NC

   (b) C2H5CN

   (c) CH3CN

   (d) CH3NC

   ›Reveal solutionSolution

   This is the carbylamine (isocyanide) test — a primary amine + chloroform + alcoholic KOH gives a foul-smelling alkyl isocyanide.

   When a primary amine reacts with chloroform in the presence of alcoholic KOH, the carbylamine reaction occurs:

   $C_2H_5NH_2 + CHCl_3 + 3KOH \xrightarrow{\Delta} C_2H_5NC + 3KCl + 3H_2O$

   …

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3. CBSE 2026Set ANNUAL1 mark
   Q.Identify the products of the following: $C_6H_5NH_2 + CHCl_3 + KOH(alc.) \rightarrow ?$

   ›Reveal solutionSolution

   This is the carbylamine (isocyanide) test, specific to primary amines: aniline reacts with chloroform and alcoholic KOH to give the foul-smelling phenyl isocyanide.

   Reaction

   $C_6H_5-NH_2 + CHCl_3 + 3KOH\ (alc.) \rightarrow C_6H_5-\overset{-}{N}\equiv \overset{+}{C} + 3KCl + 3H_2O$

   Alcoholic KOH generates dichlorocarbene ($:CCl_2$) from chloroform; this electrophilic carbene inserts into the N–H of the primary aromatic amine, and after loss of the remaining chlorines (as KCl, with KOH supplying the base) the isocyanide (carbylamine, $-NC$) functional group is formed. This reaction is diagnostic for …

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4. CBSE 2025Set ANNUAL1 markMCQ
   Q.The compound obtained by heating a mixture of 1° amine and chloroform with ethanolic KOH is -

   (a) Alkyl cyanide

   (b) Amide

   (c) Alkyl isocyanide

   (d) None of these

   ›Reveal solutionSolution

   This is the carbylamine (isocyanide) test for primary amines.

   A primary amine, on heating with chloroform and ethanolic KOH, undergoes the carbylamine reaction to form a foul-smelling alkyl isocyanide:

   $RNH_2 + CHCl_3 + 3KOH \xrightarrow{\Delta} RNC + 3KCl + 3H_2O$

   …

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5. CBSE 2025Set D1 markMCQ
   Q.Reaction of primary amine with chloroform in the presence of alcoholic KOH is called

   (a) Hydrolysis

   (b) Reduction

   (c) Wurtz reaction

   (d) Carbylamine reaction

   ›Reveal solutionSolution

   Primary amine + CHCl3 + alcoholic KOH -> isocyanide (carbylamine reaction), a test for 1deg amines.

   When a primary amine (aliphatic or aromatic) is warmed with chloroform and alcoholic potassium hydroxide, it forms an alkyl or aryl isocyanide (carbylamine), which has an extremely offensive smell:

   R-NH2 + CHCl3 + 3KOH -> R-NC + 3KCl + 3H2O

   …

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6. CBSE 2025Set ANNUAL1 markMCQ
   Q.The test which is used to distinguish between primary amine and secondary amine is

   (a) Lucas test

   (b) Carbylamine test

   (c) Fehling's test

   (d) Tollen's test

   ›Reveal solutionSolution

   The carbylamine (isocyanide) test is positive only for primary amines, so it cleanly distinguishes them from secondary (and tertiary) amines, which give no reaction.

   $\text{R-NH}_2 + \text{CHCl}_3 + 3\text{KOH (alc.)} \xrightarrow{\Delta} \text{R-NC (foul smell)} + 3\text{KCl} + 3\text{H}_2\text{O}$

   …

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7. CBSE 2025Set ANNUAL1 mark
   Q.Complete the reaction: CH3CH2NH2 + CHCl3 + 3KOH(alc.) → ?

   ›Reveal solutionSolution

   A primary amine's nitrogen attacks dichlorocarbene (generated from CHCl3+KOH), and after loss of two more HCl equivalents, an isocyanide is formed.

   This is the carbylamine (isocyanide) reaction, specific to primary amines. Alcoholic KOH first generates dichlorocarbene (:CCl₂) from chloroform by α-elimination; the primary amine's nitrogen lone pair attacks this electrophilic carbene carbon, and subsequent loss of two more equivalents of HCl (neutralized …

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8. CBSE 2024Set D1 markMCQ
   Q.Methylamine on heating with chloroform and alcoholic KOH gives

   (a) CH3OH

   (b) CH3CN

   (c) CH3CHO

   (d) CH3NC

   ›Reveal solutionSolution

   Carbylamine reaction: 1° amine + CHCl3 + alc. KOH -> isocyanide (foul smell).

   Primary amines undergo the carbylamine (isocyanide) test: heating with chloroform and alcoholic potassium hydroxide gives a foul-smelling alkyl isocyanide.

   CH3NH2 + CHCl3 + 3KOH -> CH3NC + 3KCl + 3H2O

   …

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9. CBSE 2024Set ANNUAL1 mark
   Q.Write isocyanide test for primary amines.

   ›Reveal solutionSolution

   Primary amines uniquely form foul-smelling isocyanides when heated with chloroform and alcoholic KOH; this odour is used as a positive test for primary amines (secondary/tertiary amines do not respond).

   Procedure: a small amount of the amine is warmed gently with a few drops of chloroform (CHCl3) and alcoholic potassium hydroxide (KOH).

   Reaction: R-NH2 + CHCl3 + 3KOH (alc., heat) -> R-NC (alkyl isocyanide) + 3KCl + 3H2O

   Observation: an extremely unpleasant, characteristic smell of the isocyanide (carbylamine) is produced, confirming a primary amine. …

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10. CBSE 2024Set ANNUAL1 mark
    Q.What is Carbylamine reaction?

    ›Reveal solutionSolution

    Only primary amines give this test — the offensive-smelling isocyanide product is the diagnostic signal.

    When a primary amine is heated with chloroform (CHCl3) and alcoholic potassium hydroxide (KOH), it forms an isocyanide (carbylamine), which has a characteristically unpleasant, penetrating odour:

    R-NH2 + CHCl3 + 3KOH (alc., Δ) → R-NC + 3KCl + 3H2O

    …

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11. CBSE 2023Set ANNUAL1 markMCQ
    Q.When benzyl amine is treated with chloroform in presence of ethanolic KOH, then the product formed is

    (a) structure

    (a)

    (b) structure

    (b)

    (c) structure

    (c)

    (d) structure (d)

    ›Reveal solutionSolution

    Any primary amine, treated with chloroform and ethanolic KOH, gives a foul-smelling isocyanide (carbylamine reaction) — a diagnostic test for -NH2 primary amines.

    Benzylamine is PhCH2-NH2, a primary amine (the -NH2 is on the benzylic carbon, not directly on the ring). The carbylamine reaction is:

    $R\text{-}NH_2 + CHCl_3 + 3KOH \rightarrow R\text{-}NC + 3KCl + 3H_2O$

    Here R = PhCH2-, so the product is PhCH2-NC, benzyl isocyanide — a phenyl ring bearing a -CH2NC group, exactly structure (c).

    …

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12. CBSE 2022Set GH1 markMCQ
    Q.The reaction $R-NH_2 + CHCl_3 + KOH\ (alc) \longrightarrow$ is known as:

    (a) Gattermann-Koch reaction

    (b) Carbylamine reaction

    (c) Hoffman bromomide reaction

    (d) Schmidt reaction

    ›Reveal solutionSolution

    A primary amine heated with chloroform and alcoholic KOH forms an isocyanide (carbylamine); this is the carbylamine test for $1^\circ$ amines.

    Concept — the carbylamine reaction. Aliphatic and aromatic primary amines, when warmed with chloroform and alcoholic potassium hydroxide, form isocyanides (carbylamines) — recognised by their extremely offensive smell. Secondary and tertiary amines do not give this reaction, so it is used as a test to detect a primary amino group.

    …

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