Question

Assertion (A): I-Bromopentane reacts with \(AgCN\) to give pentyl isocyanide.
Reason (R): \(AgCN\) is mainly ionic in nature.

• A. A is true, R is true and R is correct explanation of A
• B. A is true, R is true but R is not correct explanation of A
• C. A is true, R is false
• D. A is false, R is true

Hint:

Alkyl halides with \(KCN\) give alkyl cyanides because \(KCN\) is ionic, while alkyl halides with \(AgCN\) give alkyl isocyanides because \(AgCN\) is mainly covalent.

Answer 1

The Correct Option is C

Step 1: Write the reaction and identify the products.
1-Bromopentane + AgCN $\rightarrow$ Pentyl isocyanide (C₄H₉NC) rather than pentyl cyanide (C₄H₉CN). Assertion: this reaction gives isocyanide. The assertion is TRUE.
Step 2: Analyze the bonding in AgCN.
The reason relates to the nature of AgCN. The question states that the reason (R) is that AgCN is mainly ionic. Evaluate: AgCN actually has a significant COVALENT character due to the polarizable CN^- ion and Ag⁺ being a soft, polarizing metal. The bond in AgCN is mainly COVALENT, not ionic.
Step 3: Evaluate the truth of the Reason (R).
The Reason states that AgCN is mainly ionic. This is FALSE. AgCN is mainly covalent (Ag-CN bond has covalent character; it is also poorly soluble, indicating covalent nature).
Step 4: Explain the actual mechanism for isocyanide formation.
In AgCN (covalent), the Ag is bonded to C (Ag-CN). The CN^- ion attacks the alkyl halide through its C-end (since in AgCN the C is bonded to Ag, freeing the N-end to attack or more precisely the ambident nucleophile attacks via N to give isocyanide when covalent silver cyanide is used). Actually: KCN (ionic) gives cyanide (R-CN), AgCN (covalent) gives isocyanide (R-NC). The C-end attacks in KCN; N-end attacks in AgCN.
Step 5: Conclusion on Assertion and Reason.
Assertion (A) is TRUE - the reaction with AgCN gives isocyanide. Reason (R) is FALSE - AgCN is mainly covalent, not ionic. When A is true and R is false, the answer is option 3.
Step 6: Final answer.
A is true (isocyanide is formed), R is false (AgCN is mainly covalent, not ionic). The correct option is 3.
\[ \boxed{\text{A is true, R is false (option 3)}} \]