Chapter Exam

Chapter-9 Amines — Online MCQ Test

Q: Amines are organic compounds derived from ammonia by replacement of one or more hydrogen atoms with alkyl or aryl groups. Which of the following is a primary amine?

Answer: A. CH₃-NH₂ — Primary amines have one alkyl/aryl group attached to nitrogen (RNH₂). CH₃-NH₂ (methylamine) is a primary amine with one methyl group and two hydrogen atoms bonded to nitrogen.

Q: Which classification is correct for (CH₃)₂NH?

Answer: B. Secondary amine — Secondary amines have two alkyl/aryl groups attached to nitrogen (R₂NH). In (CH₃)₂NH, two methyl groups are bonded to nitrogen with one hydrogen, making it a secondary amine.

Q: What is the IUPAC name for C₂H₅-NH₂?

Answer: B. Ethylamine — C₂H₅-NH₂ contains an ethyl group (2 carbons) attached to ammonia, so it is ethylamine or ethanamine as per IUPAC nomenclature.

Q: Diazonium salts are formed by the reaction of primary aromatic amines with nitrous acid. What is the general formula for an aryl diazonium salt?

Answer: A. [Ar-N=N]⁺ X⁻ — Aryl diazonium salts have the structure [Ar-N=N]⁺ X⁻ where Ar is an aryl group and X⁻ is a counterion like Cl⁻ or BF₄⁻.

Q: Amines are basic in nature because the nitrogen atom possesses a lone pair of electrons. Arrange the following amines in order of increasing basicity in water: NH₃, CH₃NH₂, (CH₃)₂NH, (CH₃)₃N

Answer: C. (CH₃)₃N CH₃NH₂ > NH₃ > (CH₃)₃N. Secondary amines are most basic in water due to balance between electron donation and hydrogen bonding effects; tertiary amines are least basic due to steric hindrance.

Q: Gabriel's phthalimide synthesis is used for the preparation of which type of amines?

Answer: A. Primary amines — Gabriel's synthesis converts phthalimide to N-alkylphthalimide followed by hydrolysis to give primary amines. It is specific for preparing primary amines from alkyl halides.

Q: Which of the following amines will NOT undergo the Hofmann elimination reaction?

Answer: D. Primary aromatic amines — Primary aromatic amines do not undergo Hofmann elimination because the aromatic ring is not broken under these conditions. Hofmann elimination is specific for aliphatic amines and converts them to alkenes.

Q: The reaction of diazonium salts with cuprous iodide produces iodobenzene, while the same reaction with hypophosphorous acid produces benzene. What does this tell us about the reactivity of these reagents toward diazonium salts?

Answer: A. CuI is a nucleophile; H₃PO₂ is a reducing agent — CuI acts as a nucleophile, replacing the diazo group with I⁻ (Sandmeyer reaction); H₃PO₂ acts as a reducing agent, replacing the diazo group with H⁻ (Gattermann reaction), demonstrating different reaction mechanisms.

Q: A unknown primary amine C₆H₅-CH₂-NH₂ is treated with excess CH₃I followed by AgOH and heat. The major organic product would be:

Answer: B. Styrene (C₆H₅-CH=CH₂) — This is the Hofmann elimination reaction. Excess CH₃I methylates the primary amine to form the quaternary ammonium salt, which undergoes elimination with AgOH/heat, producing the alkene (styrene) as the major product.

CHEMISTRY · Grade 12 · CBSE(NCERT)

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Chapter-9 Amines — Important Questions & Answers (FAQ)

Frequently asked questions from CBSE(NCERT) Grade 12 CHEMISTRY — Chapter-9 Amines, with answers and explanations. These are sample questions; the exam has its own separate question set.

Amines are organic compounds derived from ammonia by replacement of one or more hydrogen atoms with alkyl or aryl groups. Which of the following is a primary amine?

A. CH₃-NH₂ ✓
B. CH₃-NH-CH₃
C. (CH₃)₃N
D. C₆H₅-N(CH₃)₂

Answer: A. CH₃-NH₂
Primary amines have one alkyl/aryl group attached to nitrogen (RNH₂). CH₃-NH₂ (methylamine) is a primary amine with one methyl group and two hydrogen atoms bonded to nitrogen.

Which classification is correct for (CH₃)₂NH?

A. Primary amine
B. Secondary amine ✓
C. Tertiary amine
D. Quaternary amine

Answer: B. Secondary amine
Secondary amines have two alkyl/aryl groups attached to nitrogen (R₂NH). In (CH₃)₂NH, two methyl groups are bonded to nitrogen with one hydrogen, making it a secondary amine.

What is the IUPAC name for C₂H₅-NH₂?

A. Methylamine
B. Ethylamine ✓
C. Propylamine
D. Aminoethane

Answer: B. Ethylamine
C₂H₅-NH₂ contains an ethyl group (2 carbons) attached to ammonia, so it is ethylamine or ethanamine as per IUPAC nomenclature.

Diazonium salts are formed by the reaction of primary aromatic amines with nitrous acid. What is the general formula for an aryl diazonium salt?

A. [Ar-N=N]⁺ X⁻ ✓
B. [Ar-NH-NH₂]⁺
C. Ar-N₂⁻
D. [Ar-N≡N]⁺ X⁻

Answer: A. [Ar-N=N]⁺ X⁻
Aryl diazonium salts have the structure [Ar-N=N]⁺ X⁻ where Ar is an aryl group and X⁻ is a counterion like Cl⁻ or BF₄⁻.

Amines are basic in nature because the nitrogen atom possesses a lone pair of electrons. Arrange the following amines in order of increasing basicity in water: NH₃, CH₃NH₂, (CH₃)₂NH, (CH₃)₃N

A. (CH₃)₃N < (CH₃)₂NH < CH₃NH₂ < NH₃
B. NH₃ < CH₃NH₂ < (CH₃)₂NH < (CH₃)₃N
C. (CH₃)₃N < NH₃ < CH₃NH₂ < (CH₃)₂NH ✓
D. NH₃ < (CH₃)₃N < (CH₃)₂NH < CH₃NH₂

Answer: C. (CH₃)₃N < NH₃ < CH₃NH₂ < (CH₃)₂NH
In aqueous solution, basicity order is (CH₃)₂NH > CH₃NH₂ > NH₃ > (CH₃)₃N. Secondary amines are most basic in water due to balance between electron donation and hydrogen bonding effects; tertiary amines are least basic due to steric hindrance.

Gabriel's phthalimide synthesis is used for the preparation of which type of amines?

A. Primary amines ✓
B. Secondary amines
C. Tertiary amines
D. Aromatic amines

Answer: A. Primary amines
Gabriel's synthesis converts phthalimide to N-alkylphthalimide followed by hydrolysis to give primary amines. It is specific for preparing primary amines from alkyl halides.

Which of the following amines will NOT undergo the Hofmann elimination reaction?

A. Primary aliphatic amines
B. Secondary aliphatic amines
C. Tertiary aliphatic amines
D. Primary aromatic amines ✓

Answer: D. Primary aromatic amines
Primary aromatic amines do not undergo Hofmann elimination because the aromatic ring is not broken under these conditions. Hofmann elimination is specific for aliphatic amines and converts them to alkenes.

Compare the basicity of aniline (C₆H₅NH₂) and methylamine (CH₃NH₂) in aqueous solution. Which statement is correct?

A. Aniline is more basic because aromatic rings are electron-donating
B. Methylamine is more basic due to stronger electron-donating effect of methyl group vs. phenyl group ✓
C. Both have equal basicity
D. Aniline is more basic because of resonance stabilization of the aromatic ring

Answer: B. Methylamine is more basic due to stronger electron-donating effect of methyl group vs. phenyl group
Methylamine (pKb ≈ 3.3) is more basic than aniline (pKb ≈ 9.4). The phenyl group in aniline is weakly electron-donating, and the lone pair on N is partially delocalized into the aromatic ring, reducing basicity.

The reaction of diazonium salts with cuprous iodide produces iodobenzene, while the same reaction with hypophosphorous acid produces benzene. What does this tell us about the reactivity of these reagents toward diazonium salts?

A. CuI is a nucleophile; H₃PO₂ is a reducing agent ✓
B. Both are equally reactive nucleophiles
C. H₃PO₂ is more reactive than CuI
D. Neither is reactive; the products form spontaneously

Answer: A. CuI is a nucleophile; H₃PO₂ is a reducing agent
CuI acts as a nucleophile, replacing the diazo group with I⁻ (Sandmeyer reaction); H₃PO₂ acts as a reducing agent, replacing the diazo group with H⁻ (Gattermann reaction), demonstrating different reaction mechanisms.

A unknown primary amine C₆H₅-CH₂-NH₂ is treated with excess CH₃I followed by AgOH and heat. The major organic product would be:

A. Benzylamine (C₆H₅-CH₂-NH₂)
B. Styrene (C₆H₅-CH=CH₂) ✓
C. Methylbenzene/Toluene (C₆H₅-CH₃)
D. N,N-dimethylbenzylamine (C₆H₅-CH₂-N(CH₃)₂)

Answer: B. Styrene (C₆H₅-CH=CH₂)
This is the Hofmann elimination reaction. Excess CH₃I methylates the primary amine to form the quaternary ammonium salt, which undergoes elimination with AgOH/heat, producing the alkene (styrene) as the major product.

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