JEE Main 2024 — Chemistry Organic Chemistry

2024mcqmedium

Given below are two statements : one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R).$

Assertion $(A):$ Haloalkanes react with $\mathrm{KCN}$ to form alkyl cyanides as a main product while with $\mathrm{AgCN}$ form isocyanide as the main product.

Reason $(R):$ $\mathrm{KCN}$ and $\mathrm{AgCN}$ both are highly ionic compounds.

In the light of the above statement, choose the most appropriate answer from the options given below.

Official previous-year question

Held on 1 Feb 2024 · Verified 6 Jul 2026.

Options

A
$(A)$ is correct but $(R)$ is not correct
B
Both $(A)$ and $(R)$ are correct but $(R)$ is not the correct explanation of $(A)$
C
$(A)$ is not correct but $(R)$ is correct
D
Both $(A)$ and $(R)$ are correct and $(R)$ is the correct explanation of $(A)$

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Solution

$\mathrm{KCN}$ is ionic in nature and provides cyanide ions in solution. Although both carbon and nitrogen atoms are in a position to donate electron pairs, the attack takes place mainly

through carbon atom and not through nitrogen atom since $C-C$ bond is more stable than $C-N$ bond.

Involved reaction is shown below:

$R-X\overset{}{\overset{\mathrm{Substitution}\mathrm{reaction}}{\rightarrow }R-\mathrm{CN}+\mathrm{KX}} \mathrm{Alkyl}\mathrm{halide}\mathrm{Cyanide}$

Reaction of alkyl halide with $\mathrm{AgCN}$

$\mathrm{AgCN}$ is mainly covalent in nature. Here only nitrogen is free to donate electron pairs,hence it forms isocyanide as the main product.

Involved reaction is shown below:

$R-X+\mathrm{AgCN}\overset{\mathrm{Substitution}\mathrm{reaction}}{\rightarrow }R-\mathrm{NC}+\mathrm{AgX} \mathrm{Alkyl}\mathrm{halide}\mathrm{Isocyanide}$

Hence, here isocyanide is formed as major product.

JEE Main 2024 Chemistry, Haloalkanes and Haloarenes — solution figure

$\mathrm{AgCN}$ is mainly covalent in nature and nitrogen is available for attack, so alkyl isocyanide is formed as main product.

Cyanide ion is an ambidentate ligand (nucleophile or lewis base). It means that donation of a pair of electrons can be through either carbon or nitrogen, so it has two nucleophilic centres. $\mathrm{KCN}$ is predominantly ionic and $\mathrm{AgCN}$ is predominantly covalent.

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Solution

$\mathrm{KCN}$ is ionic in nature and provides cyanide ions in solution. Although both carbon and nitrogen atoms are in a position to donate electron pairs, the attack takes place mainly

through carbon atom and not through nitrogen atom since $C-C$ bond is more stable than $C-N$ bond.

Involved reaction is shown below:

$R-X\overset{}{\overset{\mathrm{Substitution}\mathrm{reaction}}{\rightarrow }R-\mathrm{CN}+\mathrm{KX}} \mathrm{Alkyl}\mathrm{halide}\mathrm{Cyanide}$

Reaction of alkyl halide with $\mathrm{AgCN}$

$\mathrm{AgCN}$ is mainly covalent in nature. Here only nitrogen is free to donate electron pairs,hence it forms isocyanide as the main product.

Involved reaction is shown below:

$R-X+\mathrm{AgCN}\overset{\mathrm{Substitution}\mathrm{reaction}}{\rightarrow }R-\mathrm{NC}+\mathrm{AgX} \mathrm{Alkyl}\mathrm{halide}\mathrm{Isocyanide}$

Hence, here isocyanide is formed as major product.

JEE Main 2024 Chemistry, Haloalkanes and Haloarenes — solution figure

$\mathrm{AgCN}$ is mainly covalent in nature and nitrogen is available for attack, so alkyl isocyanide is formed as main product.

JEE Main 2024 — Chemistry Organic Chemistry

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Solution

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JEE Main 2024 — Chemistry Organic Chemistry

Options

Did you get this right?

Solution

Your note

JEE Main Organic Chemistry in other years

More JEE Main Organic Chemistry questions

Other Chemistry topics for JEE Main

Physical Chemistry

Inorganic Chemistry

Keep practicing Organic Chemistry