301. Which compound can be prepared by reducing nitrobenzene?
ⓐ. Benzonitrile
ⓑ. Benzylamine
ⓒ. Benzamide
ⓓ. Aniline
Correct Answer: Aniline
Explanation: Nitrobenzene contains the nitro group directly attached to a benzene ring. Reduction converts this \(-NO_2\) group into \(-NH_2\), giving \(C_6H_5NH_2\). \(C_6H_5NH_2\) is aniline. Benzylamine, benzamide, and benzonitrile have different bonding patterns and are not the direct products of simple nitrobenzene reduction.
302. Which statement correctly compares reduction of aliphatic and aromatic nitro compounds?
ⓐ. Only aliphatic nitro compounds form amines on reduction.
ⓑ. Only aromatic nitro compounds form amines on reduction.
ⓒ. Both give nitriles first as the final isolated product.
ⓓ. Both can give corresponding amines on reduction.
Correct Answer: Both can give corresponding amines on reduction.
Explanation: Nitro compounds, whether aliphatic or aromatic, can be reduced to amines. An aliphatic example is \(RNO_2 \rightarrow RNH_2\). An aromatic example is \(C_6H_5NO_2 \rightarrow C_6H_5NH_2\). The nature of \(R\) affects the identity of the amine product, but the functional-group conversion remains reduction of \(-NO_2\) to \(-NH_2\).
303. Which route is most direct for preparing aniline from nitrobenzene?
ⓐ. Treat with \(NaNO_2/HCl\) at low temperature
ⓑ. Reduce with \(Sn/HCl\), then add alkali
ⓒ. Heat with \(CHCl_3\) and alcoholic \(KOH\)
ⓓ. React with \(CH_3COCl\) in base
Correct Answer: Reduce with \(Sn/HCl\), then add alkali
Explanation: Nitrobenzene is converted into aniline by reducing the nitro group to an amino group. \(Sn/HCl\) is a standard acidic reducing system for this conversion. Under acidic conditions, the amine may be present as its salt, so alkali is used to free aniline. \(NaNO_2/HCl\) is used after aniline has already been formed, not before.
304. Which statement about reduction of nitro compounds is accurate?
ⓐ. The nitro group remains unchanged and only the carbon chain is reduced.
ⓑ. The nitro group is replaced by a carbonyl group.
ⓒ. The nitro group is converted into an amino group.
ⓓ. The nitro group is converted into a diazonium group directly.
Correct Answer: The nitro group is converted into an amino group.
Explanation: Reduction of nitro compounds changes the \(-NO_2\) group into \(-NH_2\). This conversion is one of the most important methods for preparing amines, especially aromatic amines such as aniline. The carbon skeleton usually remains the same during this transformation. Diazonium salts are formed later from primary aromatic amines by diazotisation, not directly from nitro compounds.
305. Which reagent is suitable for reducing a nitrile to a primary amine?
ⓐ. \(NaNO_2/HCl\)
ⓑ. \(LiAlH_4\)
ⓒ. \(CuCl/HCl\)
ⓓ. \(Br_2/NaOH\)
Correct Answer: \(LiAlH_4\)
Explanation: Nitriles, \(RCN\), can be reduced to primary amines, \(RCH_2NH_2\). \(LiAlH_4\) is a strong reducing agent commonly used for this conversion. The carbon of the nitrile group is retained and becomes the \(CH_2\) group attached to \(-NH_2\). \(NaNO_2/HCl\) is used for diazotisation, while \(Br_2/NaOH\) is used in Hoffmann bromamide degradation.
306. Which equation represents reduction of a nitrile to a primary amine?
ⓐ. \(RCN + H_2O \rightarrow RCONH_2\)
ⓑ. \(RCN + NH_3 \rightarrow RCH_2CN\)
ⓒ. \(RCN + 2H_2O \rightarrow RCOOH + NH_3\)
ⓓ. \(RCN + 2H_2 \rightarrow RCH_2NH_2\)
Correct Answer: \(RCN + 2H_2 \rightarrow RCH_2NH_2\)
Explanation: \(\textbf{Starting group:}\)
A nitrile has the general formula \(RCN\).
\(\textbf{Reaction type:}\)
Reduction adds hydrogen across the nitrile group.
\(\textbf{Carbon retention:}\)
The carbon of the \(CN\) group remains in the product as the \(CH_2\) carbon.
\(\textbf{Product formed:}\)
The final product is a primary amine, \(RCH_2NH_2\).
\(\textbf{Balanced form:}\)
\[\boxed{RCN + 2H_2 \rightarrow RCH_2NH_2}\]
307. What is the main product when \(CH_3CN\) is reduced completely?
ⓐ. \(CH_3CH_2NH_2\)
ⓑ. \(CH_3NH_2\)
ⓒ. \(CH_3CONH_2\)
ⓓ. \(CH_3CH_2NO_2\)
Correct Answer: \(CH_3CH_2NH_2\)
Explanation: \(\textbf{Starting compound:}\)
\(CH_3CN\) is ethanenitrile.
\(\textbf{Reduction pattern:}\)
A nitrile, \(RCN\), is reduced to \(RCH_2NH_2\).
\(\textbf{Identify }R\textbf{:}\)
Here, \(R = CH_3\).
\(\textbf{Apply the pattern:}\)
\(CH_3CN\) becomes \(CH_3CH_2NH_2\).
\(\textbf{Final Answer:}\)
Reduction of \(CH_3CN\) gives ethylamine, \(CH_3CH_2NH_2\).
308. Which product is obtained by reducing \(CH_3CH_2CN\) with \(LiAlH_4\)?
ⓐ. \(CH_3CH_2NH_2\)
ⓑ. \(CH_3CH_2CH_2NO_2\)
ⓒ. \(CH_3CH_2CH_2NH_2\)
ⓓ. \(CH_3CH_2NO_2\)
Correct Answer: \(CH_3CH_2CH_2NH_2\)
Explanation: \(\textbf{Starting compound:}\)
\(CH_3CH_2CN\) is propanenitrile.
\(\textbf{Useful conversion:}\)
\[
RCN \rightarrow RCH_2NH_2
\]
\(\textbf{Identify }R\textbf{:}\)
For \(CH_3CH_2CN\), the \(R\) group is \(CH_3CH_2-\).
\(\textbf{Product formation:}\)
The nitrile carbon becomes \(CH_2\), giving \(CH_3CH_2CH_2NH_2\).
\(\textbf{Final Answer:}\)
The product is propan-1-amine, \(CH_3CH_2CH_2NH_2\).
309. Which statement correctly describes the carbon-count change during reduction of \(RCN\) to \(RCH_2NH_2\)?
ⓐ. One carbon atom is lost from the molecule.
ⓑ. The nitrile carbon is retained.
ⓒ. Two new carbon atoms are added to the chain.
ⓓ. The carbon chain is converted into a benzene ring.
Correct Answer: The nitrile carbon is retained.
Explanation: In nitrile reduction, the carbon atom of the \(CN\) group does not leave the molecule. It is converted into the \(CH_2\) carbon attached to the amino group in \(RCH_2NH_2\). This makes nitrile reduction useful for preparing amines with one more carbon than the original alkyl group \(R\). It is different from Hoffmann bromamide degradation, where a carbonyl carbon is lost.
310. Which two-step route can convert \(CH_3Br\) into \(CH_3CH_2NH_2\) with one-carbon chain extension?
ⓐ. \(KCN\), then reduction
ⓑ. \(NaOH\), then oxidation
ⓒ. \(Br_2/NaOH\), then hydrolysis
ⓓ. \(NaNO_2/HCl\), then warming
Correct Answer: \(KCN\), then reduction
Explanation: \(\textbf{Starting compound:}\)
\(CH_3Br\) has one carbon atom.
\(\textbf{Chain-extension step:}\)
Reaction with \(KCN\) gives \(CH_3CN\), adding the nitrile carbon to the chain.
\(\textbf{Reduction step:}\)
Reduction of \(CH_3CN\) gives \(CH_3CH_2NH_2\).
\(\textbf{Carbon-count check:}\)
The product has two carbon atoms, so the route extends the chain by one carbon.
\(\textbf{Final Answer:}\)
The suitable sequence is \(KCN\), followed by reduction.
311. Which conversion shows the chain-extension feature of nitrile reduction?
ⓐ. \(CH_3CONH_2 \rightarrow CH_3NH_2\)
ⓑ. \(C_6H_5NO_2 \rightarrow C_6H_5NH_2\)
ⓒ. \(CH_3CH_2Br \rightarrow CH_3CH_2OH\)
ⓓ. \(CH_3CN \rightarrow CH_3CH_2NH_2\)
Correct Answer: \(CH_3CN \rightarrow CH_3CH_2NH_2\)
Explanation: \(CH_3CN\) has two carbon atoms, and reduction gives \(CH_3CH_2NH_2\), also with two carbon atoms. If \(CH_3CN\) was prepared from \(CH_3X\) through cyanide substitution, the nitrile carbon represents one-carbon chain extension relative to the original methyl halide. The nitrile carbon becomes the \(CH_2\) carbon in the amine. This carbon-retention feature is characteristic of nitrile reduction.
312. Which product is formed when benzonitrile, \(C_6H_5CN\), is reduced?
ⓐ. \(C_6H_5CH_2NH_2\)
ⓑ. \(C_6H_5NH_2\)
ⓒ. \(C_6H_5CH_2NHCH_3\)
ⓓ. \(C_6H_5NO_2\)
Correct Answer: \(C_6H_5CH_2NH_2\)
Explanation: \(\textbf{Starting compound:}\)
Benzonitrile is \(C_6H_5CN\).
\(\textbf{Reduction pattern:}\)
A nitrile group, \(-CN\), is reduced to \(-CH_2NH_2\).
\(\textbf{Apply to benzonitrile:}\)
The ring remains unchanged, and the nitrile carbon becomes a \(CH_2\) group.
\(\textbf{Product:}\)
The product is benzylamine, \(C_6H_5CH_2NH_2\).
\(\textbf{Final Answer:}\)
Reduction of benzonitrile gives \(C_6H_5CH_2NH_2\).
313. Why does reduction of \(C_6H_5CN\) give benzylamine rather than aniline?
ⓐ. The nitrile carbon remains as \(CH_2\) between the ring and \(NH_2\).
ⓑ. The benzene ring is completely reduced to cyclohexane.
ⓒ. The nitrile nitrogen attaches directly to the aromatic ring.
ⓓ. The \(CN\) group is replaced by hydrogen before reduction.
Correct Answer: The nitrile carbon remains as \(CH_2\) between the ring and \(NH_2\).
Explanation: In benzonitrile, the nitrile carbon is directly attached to the benzene ring. On reduction, the \(CN\) carbon is not removed; it becomes the \(CH_2\) group of \(C_6H_5CH_2NH_2\). Aniline, \(C_6H_5NH_2\), would require nitrogen directly attached to the ring without a \(CH_2\) spacer. Therefore, nitrile reduction of benzonitrile gives benzylamine, not aniline.
314. Which statement is correct for reducing \(RCN\) with catalytic hydrogenation?
ⓐ. The product is a primary amine.
ⓑ. The product is a tertiary amine.
ⓒ. The product is a nitro compound.
ⓓ. The product is an amide only.
Correct Answer: The product is a primary amine.
Explanation: Catalytic hydrogenation of a nitrile reduces the \(C \equiv N\) group. The nitrile carbon becomes \(CH_2\), and nitrogen becomes part of the \(-NH_2\) group. This gives \(RCH_2NH_2\), a primary amine. The reaction does not directly give a tertiary amine because only one carbon group is attached to nitrogen in the product.
315. Which compound gives \(CH_3CH_2CH_2NH_2\) on reduction?
ⓐ. \(CH_3CH_2NO_2\)
ⓑ. \(CH_3CH_2CN\)
ⓒ. \(CH_3CH_2COOH\)
ⓓ. \(CH_3CN\)
Correct Answer: \(CH_3CH_2CN\)
Explanation: \(\textbf{Target product:}\)
The product is \(CH_3CH_2CH_2NH_2\), a three-carbon primary amine.
\(\textbf{Nitrile reduction rule:}\)
\(RCN\) gives \(RCH_2NH_2\).
\(\textbf{Work backward:}\)
To get \(CH_3CH_2CH_2NH_2\), \(R\) must be \(CH_3CH_2-\).
\(\textbf{Starting nitrile:}\)
The required nitrile is \(CH_3CH_2CN\).
\(\textbf{Final Answer:}\)
Reduction of \(CH_3CH_2CN\) gives \(CH_3CH_2CH_2NH_2\).
316. Which comparison between reduction of nitroethane and ethanenitrile is accurate?
ⓐ. Both give \(CH_3NH_2\) as the main product.
ⓑ. Both give \(CH_3CH_2NH_2\).
ⓒ. Nitroethane gives \(CH_3NH_2\), while ethanenitrile gives \(CH_3CH_2NH_2\).
ⓓ. Both give \(CH_3CONH_2\) as the main product.
Correct Answer: Both give \(CH_3CH_2NH_2\).
Explanation: Nitroethane, \(CH_3CH_2NO_2\), is reduced by converting \(-NO_2\) into \(-NH_2\), so it gives \(CH_3CH_2NH_2\). Ethanenitrile, \(CH_3CN\), is reduced by converting the nitrile carbon into \(CH_2\), also giving \(CH_3CH_2NH_2\). The two starting compounds reach the same product by different functional-group reductions. This comparison is useful because the carbon-count logic is different in the two routes.
317. Which starting nitrile should be reduced to prepare \(C_2H_5CH_2NH_2\)?
ⓐ. \(CH_3CN\)
ⓑ. \(C_2H_5CN\)
ⓒ. \(C_2H_5NO_2\)
ⓓ. \(C_2H_5CONH_2\)
Correct Answer: \(C_2H_5CN\)
Explanation: \(\textbf{Target product:}\)
\(C_2H_5CH_2NH_2\) has the form \(RCH_2NH_2\).
\(\textbf{Nitrile reduction pattern:}\)
\(RCN\) reduces to \(RCH_2NH_2\).
\(\textbf{Identify }R\textbf{:}\)
In \(C_2H_5CH_2NH_2\), \(R = C_2H_5\).
\(\textbf{Required nitrile:}\)
The corresponding nitrile is \(C_2H_5CN\).
\(\textbf{Final Answer:}\)
The starting nitrile should be \(C_2H_5CN\).
318. Which reaction best distinguishes nitrile reduction from Hoffmann bromamide degradation by carbon count?
ⓐ. \(RCN\) retains its nitrile carbon; \(RCONH_2\) loses its carbonyl carbon.
ⓑ. \(RCN\) loses its nitrile carbon; \(RCONH_2\) retains its carbonyl carbon.
ⓒ. Both \(RCN\) and \(RCONH_2\) retain the functional-group carbon.
ⓓ. Both \(RCN\) and \(RCONH_2\) lose the functional-group carbon.
Correct Answer: \(RCN\) retains its nitrile carbon; \(RCONH_2\) loses its carbonyl carbon.
Explanation: Nitrile reduction keeps the carbon of the nitrile group in the product, so \(RCN\) becomes \(RCH_2NH_2\). Hoffmann bromamide degradation behaves differently: \(RCONH_2\) gives \(RNH_2\), and the carbonyl carbon is lost. This contrast is one of the most important carbon-count traps in amine preparation. The two methods should not be interchanged when planning a synthesis.
319. Which product is obtained when \(CH_3CH_2CH_2CN\) is reduced?
ⓐ. \(CH_3CH_2CH_2NH_2\)
ⓑ. \(CH_3CH_2CH_2CH_2NH_2\)
ⓒ. \(CH_3CH_2CONH_2\)
ⓓ. \(CH_3CH_2CH_2CH_2NO_2\)
Correct Answer: \(CH_3CH_2CH_2CH_2NH_2\)
Explanation: \(\textbf{Starting nitrile:}\)
\(CH_3CH_2CH_2CN\) has the form \(RCN\), where \(R = CH_3CH_2CH_2-\).
\(\textbf{Reduction rule:}\)
A nitrile reduces to \(RCH_2NH_2\).
\(\textbf{Apply the rule:}\)
\(CH_3CH_2CH_2CN\) becomes \(CH_3CH_2CH_2CH_2NH_2\).
\(\textbf{Carbon-count check:}\)
The nitrile carbon is retained as the \(CH_2\) group next to \(NH_2\).
\(\textbf{Final Answer:}\)
The product is \(CH_3CH_2CH_2CH_2NH_2\).
320. Which statement correctly describes why nitrile reduction is useful in synthesis planning?
ⓐ. It removes nitrogen completely from the molecule.
ⓑ. It always converts aromatic rings into aliphatic chains.
ⓒ. It gives a primary amine without losing the nitrile carbon.
ⓓ. It always produces secondary amines from primary alkyl halides.
Correct Answer: It gives a primary amine without losing the nitrile carbon.
Explanation: Nitrile reduction converts \(RCN\) into \(RCH_2NH_2\). The carbon of the nitrile group becomes part of the final carbon skeleton, so this route can help prepare amines with a planned carbon count. It gives primary amines rather than secondary amines. The method is especially useful when the nitrile has been prepared from an alkyl halide using cyanide substitution, because the \(CN\) carbon extends the chain by one carbon.
