Consider the following sequence of reactions and identify \( A \), \( B \), and \( C \) respectively.
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When working with aromatic compounds, use the appropriate reagents to form diazonium salts and understand their subsequent reactions such as coupling and bromination.
To identify compounds \( A \), \( B \), and \( C \) in the given sequence of reactions, let's analyze each step using our knowledge of organic chemistry reactions.
Conversion of Aniline to Diazonium Salt: The first step involves the reaction of aniline (\(\text{C}_6\text{H}_5\text{NH}_2\)) with \(\text{NaNO}_2\) and \(\text{HCl}\) at \(0-5^\circ\text{C}\). This forms a diazonium salt (\(\text{C}_6\text{H}_5\text{N}_2^+\text{Cl}^-\)). This reaction is known as diazotization.
Therefore, compound \( A \) is the diazonium salt: \(\text{C}_6\text{H}_5\text{N}_2^+\).
Conversion of Diazonium Salt to Benzene: In the second step, the diazonium salt is treated with \(\text{H}_3\text{PO}_2\). This reaction replaces the diazonium group with hydrogen, resulting in the formation of benzene (\(\text{C}_6\text{H}_6\)).
Therefore, compound \( B \) is benzene: \(\text{C}_6\text{H}_6\).
Bromination of Benzene: The final step involves the bromination of benzene using \(\text{Br}_2\) in the presence of a catalyst \(\text{FeBr}_3\). This leads to the formation of bromobenzene (\(\text{C}_6\text{H}_5\text{Br}\)).
Therefore, compound \( C \) is bromobenzene: \(\text{C}_6\text{H}_5\text{Br}\).
Combining these steps, the correct sequence is: \( A \) is \(\text{C}_6\text{H}_5\text{N}_2^+\), \( B \) is \(\text{C}_6\text{H}_6\), and \( C \) is \(\text{C}_6\text{H}_5\text{Br}\).
Therefore, the correct answer is: \( \text{C}_6\text{H}_5\text{N}_2^+, \, \text{C}_6\text{H}_6, \, \text{C}_6\text{H}_5\text{Br} \).
