Class 12 Chemistry

Chapter 9 Solutions — Amines

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Solutions

Overview

Step-by-step NCERT solutions for Amines (Chapter 9, CBSE Class 12 Chemistry) — every question and answer worked out in full, not just the final result. You can also read the Amines textbook chapter.

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All 14 questions in Amines are solved in the PDF. Here's what's inside, exercise by exercise:

Exercises

1.
Write IUPAC names of the following compounds and classify them into primary, secondary and tertiary amines:
- (i) (CH₃)₂CHNH₂
- (ii) CH₃(CH₂)₂NH₂
- (iii) CH₃NHCH(CH₃)₂
- (iv) (CH₃)₃CNH₂
- (v) C₆H₅NHCH₃
- (vi) (CH₃CH₂)₂NCH₃
- (vii) m-BrC₆H₄NH₂
2.
Give one chemical test to distinguish between the following pairs of compounds:
- (i) Methylamine and dimethylamine
- (ii) Secondary and tertiary amines
- (iii) Ethylamine and aniline
- (iv) Aniline and benzylamine
- (v) Aniline and N-methylaniline.
3.
Account for the following:
- (i) pKb of aniline is more than that of methylamine.
- (ii) Ethylamine is soluble in water whereas aniline is not.
- (iii) Methylamine in water reacts with ferric chloride to precipitate hydrated ferric oxide.
- (iv) Although amino group is o- and p-directing in aromatic electrophilic substitution reactions, aniline on nitration gives a substantial amount of m-nitroaniline…
4.
Arrange the following:
- (i) In decreasing order of the pKb values: C₂H₅NH₂, C₆H₅NHCH₃, (C₂H₅)₂NH and C₆H₅NH₂.
- (ii) In increasing order of basic strength: C₆H₅NH₂, C₆H₅N(CH₃)₂, (C₂H₅)₂NH and CH₃NH₂.
- (iii) In increasing order of basic strength:
- (a) Aniline, p-nitroaniline and p-toluidine;
- (b) C₆H₅NH₂, C₆H₅NHCH₃, C₆H₅CH₂NH₂.
- (iv) In decreasing order of basic strength in gas phase: C₂H₅NH₂…
5.
How will you convert:
- (i) Ethanoic acid into methanamine
- (ii) Hexanenitrile into 1-aminopentane
- (iii) Methanol to ethanoic acid
- (iv) Ethanamine into methanamine
- (v) Ethanoic acid into propanoic acid
- (vi) Methanamine into ethanamine
- (vii) Nitromethane into dimethylamine
- (viii) Propanoic acid into ethanoic acid?
Describe a method for the identification of primary, secondary and tertiary amines. Also write chemical equations of the reactions involved.
7.
Write short notes on the following:
- (i) Carbylamine reaction
- (ii) Diazotisation
- (iii) Hofmann's bromamide reaction
- (iv) Coupling reaction
- (v) Ammonolysis
- (vi) Acetylation
- (vii) Gabriel phthalimide synthesis.
8.
Accomplish the following conversions:
- (i) Nitrobenzene to benzoic acid
- (ii) Benzene to m-bromophenol
- (iii) Benzoic acid to aniline
- (iv) Aniline to 2,4,6-tribromofluorobenzene
- (v) Benzyl chloride to 2-phenylethanamine
- (vi) Chlorobenzene to p-chloroaniline
- (vii) Aniline to p-bromoaniline
- (viii) Benzamide to toluene
- (ix) Aniline to benzyl alcohol.
9.
Give the structures of A, B and C in the following reactions:
- (i) CH₃CH₂I -(NaCN)-> A -(OH⁻, partial hydrolysis)-> B -(NaOH + Br₂)-> C
- (ii) C₆H₅N₂Cl -(CuCN)-> A -(H₂O/H⁺)-> B -(NH₃)-> C
- (iii) CH₃CH₂Br -(KCN)-> A -(LiAlH₄)-> B -(HNO₂, 0 C)-> C
- (iv) C₆H₅NO₂ -(Fe/HCl)-> A -(NaNO₂/HCl, 273 K)-> B -(H₂O/H⁺)-> C
- (v) CH₃COOH -(NH₃)-> A -(NaOBr)-> B -(NaNO₂/HCl)-> C
- (vi) C₆H₅NO₂ -(Fe/HCl)-> A -(HNO₂…
An aromatic compound 'A' on treatment with aqueous ammonia and heating forms compound 'B' which on heating with Br₂ and KOH forms a compound 'C' of molecular formula C₆H₇N. Write the structures and IUPAC names of compounds A, B and C.
11.
Complete the following reactions:
- (i) C₆H₅NH₂ + CHCl₃ + alc. KOH ->
- (ii) C₆H₅N₂Cl + H₃PO₂ + H₂O ->
- (iii) C₆H₅NH₂ + H₂SO₄ (conc.) ->
- (iv) C₆H₅N₂Cl + C₂H₅OH ->
- (v) C₆H₅NH₂ + Br₂(aq) ->
- (vi) C₆H₅NH₂ + (CH₃CO)₂O ->
- (vii) C₆H₅N₂Cl -(i) HBF₄
- (ii) NaNO₂/Cu, heat->
Why cannot aromatic primary amines be prepared by Gabriel phthalimide synthesis?
13.
Write the reactions of
- (i) aromatic and
- (ii) aliphatic primary amines with nitrous acid.
14.
Give plausible explanation for each of the following:
- (i) Why are amines less acidic than alcohols of comparable molecular masses?
- (ii) Why do primary amines have higher boiling point than tertiary amines?
- (iii) Why are aliphatic amines stronger bases than aromatic amines?

Sample

Worked examples

3 questions from Amines, solved step by step.

Exercises

Write IUPAC names of the following compounds and classify them into primary, secondary and tertiary amines: (i) (CH₃)₂CHNH₂ (ii) CH₃(CH₂)₂NH₂ (iii) CH₃NHCH(CH₃)₂ (iv) (CH₃)₃CNH₂ (v) C₆H₅NHCH₃ (vi) (CH₃CH₂)₂NCH₃ (vii) m-BrC₆H₄NH₂

(i) (CH₃)₂CHNH₂ — Propan-2-amine (1°)

(ii) CH₃(CH₂)₂NH₂ — Propan-1-amine (1°)

(iii) CH₃NHCH(CH₃)₂ — N-Methylpropan-2-amine (2°)

(iv) (CH₃)₃CNH₂ — 2-Methylpropan-2-amine (1°)

(v) C₆H₅NHCH₃ — N-Methylaniline / N-methylbenzenamine (2°)

(vi) (CH₃CH₂)₂NCH₃ — N-Ethyl-N-methylethanamine (3°)

(vii) m-BrC₆H₄NH₂ — 3-Bromoaniline / 3-bromobenzenamine (1°)

Answer: (i) propan-2-amine, 1° (ii) propan-1-amine, 1° (iii) N-methylpropan-2-amine, 2° (iv) 2-methylpropan-2-amine, 1° (v) N-methylaniline, 2° (vi) N-ethyl-N-methylethanamine, 3° (vii) 3-bromoaniline, 1°

Exercises

Give one chemical test to distinguish between the following pairs of compounds: (i) Methylamine and dimethylamine (ii) Secondary and tertiary amines (iii) Ethylamine and aniline (iv) Aniline and benzylamine (v) Aniline and N-methylaniline.

(i) Methylamine (1°) and dimethylamine (2°): Carbylamine test. Methylamine (1°) + CHCl₃ + alc. KOH gives foul-smelling methyl isocyanide; dimethylamine (2°) gives no such smell.

(ii) 2° and 3° amines: Hinsberg's test with benzenesulphonyl chloride. A 2° amine gives an N,N-disubstituted sulphonamide insoluble in KOH; a 3° amine does not react.

(iii) Ethylamine and aniline: Add to bromine water. Aniline gives a white precipitate (2,4,6-tribromoaniline); ethylamine does not. (Also, aniline gives an orange azo dye in the diazotisation-coupling test; ethylamine evolves N₂.)

(iv) Aniline and benzylamine: Diazotisation. Aniline (aromatic 1° amine) with HNO₂ at 273-278 K gives a stable diazonium salt (dye test positive); benzylamine (aliphatic 1° amine) evolves N₂ gas with effervescence.

(v) Aniline (1°) and N-methylaniline (2°): Hinsberg's test — aniline gives a sulphonamide soluble in KOH (acidic N-H); N-methylaniline gives one insoluble in KOH.

Answer: (i) carbylamine test (ii) Hinsberg's test (iii) bromine water / dye test (iv) nitrous acid (stable diazonium vs N₂) (v) Hinsberg's test

Exercises

How will you convert: (i) Ethanoic acid into methanamine (ii) Hexanenitrile into 1-aminopentane (iii) Methanol to ethanoic acid (iv) Ethanamine into methanamine (v) Ethanoic acid into propanoic acid (vi) Methanamine into ethanamine (vii) Nitromethane into dimethylamine (viii) Propanoic acid into ethanoic acid?

(i) CH₃COOH → (NH₃, heat) CH₃CONH₂ → (Br₂ + KOH, Hofmann bromamide) CH₃NH₂ (methanamine).

(ii) CH₃(CH₂)₄CN → (H₃O⁺ hydrolysis) CH₃(CH₂)₄COOH → (NH₃, heat) CH₃(CH₂)₄CONH₂ → (Br₂ + KOH, Hofmann) CH₃(CH₂)₃CH₂NH₂ = pentan-1-amine (1-aminopentane).

(iii) CH₃OH → (HBr / red P) CH₃Br → (alc. KCN) CH₃CN → (H₃O⁺ hydrolysis) CH₃COOH (ethanoic acid).

(iv) C₂H₅NH₂ → (HNO₂) C₂H₅OH → ([O]) CH₃COOH → (NH₃, heat) CH₃CONH₂ → (Br₂ + KOH, Hofmann) CH₃NH₂ (methanamine).

(v) CH₃COOH → (LiAlH₄) C₂H₅OH → (PBr₃) C₂H₅Br → (alc. KCN) C₂H₅CN → (H₃O⁺ hydrolysis) C₂H₅COOH (propanoic acid).

(vi) CH₃NH₂ → (HNO₂) CH₃OH → (HBr) CH₃Br → (alc. KCN) CH₃CN → (LiAlH₄) C₂H₅NH₂ (ethanamine).

(vii) CH₃NO₂ → (Sn/HCl reduction) CH₃NH₂; then CH₃NH₂ + CH₃I (controlled) → (CH₃)₂NH (dimethylamine) [remove excess by fractional distillation].

(viii) C₂H₅COOH → (NH₃, heat) C₂H₅CONH₂ → (Br₂ + KOH, Hofmann) C₂H₅NH₂ → (HNO₂) C₂H₅OH → ([O]) CH₃COOH (ethanoic acid).

Answer: (i)-(viii) achieved by ascending (nitrile route: -X/KCN then hydrolysis, adds 1 C) or descending (Hofmann bromamide on the amide, removes 1 C) the series, plus HNO₂ on 1° amines to give the alcohol

All 14 questions in Amines are solved step by step in the Solutions PDF above.

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Chapter 9 Solutions — Amines

Overview

What these solutions cover

Exercises

Worked examples

Write IUPAC names of the following compounds and classify them into primary, secondary and tertiary amines: (i) (CH₃)₂CHNH₂ (ii) CH₃(CH₂)₂NH₂ (iii) CH₃NHCH(CH₃)₂ (iv) (CH₃)₃CNH₂ (v) C₆H₅NHCH₃ (vi) (CH₃CH₂)₂NCH₃ (vii) m-BrC₆H₄NH₂

Give one chemical test to distinguish between the following pairs of compounds: (i) Methylamine and dimethylamine (ii) Secondary and tertiary amines (iii) Ethylamine and aniline (iv) Aniline and benzylamine (v) Aniline and N-methylaniline.

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