Consider the following compounds :
\( \text{C}_2\text{H}_5\text{NH}_2, (\text{C}_2\text{H}_5)_2\text{NH}, \text{C}_6\text{H}_5\text{CH}_2\text{NH}_2, \text{NH}_3, \text{C}_6\text{H}_5\text{NH}_2 \)
The correct increasing order of the above compounds on the basis of their basic strength is :
\( \text{C}_2\text{H}_5\text{NH}_2, (\text{C}_2\text{H}_5)_2\text{NH}, \text{C}_6\text{H}_5\text{CH}_2\text{NH}_2, \text{NH}_3, \text{C}_6\text{H}_5\text{NH}_2 \)
The correct increasing order of the above compounds on the basis of their basic strength is :
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For ethyl substituted amines in water, the order is 2, 1, 3 (213).
For methyl substituted amines in water, the order is 2, 3, 1 (231).
- \( \text{C}_6\text{H}_5\text{NH}_2 \lt \text{NH}_3 \lt \text{C}_6\text{H}_5\text{CH}_2\text{NH}_2 \lt \text{C}_2\text{H}_5\text{NH}_2 \lt (\text{C}_2\text{H}_5)_2\text{NH} \)
- \( \text{NH}_3 \lt \text{C}_6\text{H}_5\text{NH}_2 \lt \text{C}_6\text{H}_5\text{CH}_2\text{NH}_2 \lt \text{C}_2\text{H}_5\text{NH}_2 \lt (\text{C}_2\text{H}_5)_2\text{NH} \)
- \( \text{C}_6\text{H}_5\text{CH}_2\text{NH}_2 \lt (\text{C}_2\text{H}_5)_2\text{NH} \lt \text{NH}_3 \lt \text{C}_6\text{H}_5\text{NH}_2 \lt \text{C}_2\text{H}_5\text{NH}_2 \)
- \( \text{C}_2\text{H}_5\text{NH}_2 \lt \text{C}_6\text{H}_5\text{NH}_2 \lt \text{NH}_3 \lt \text{C}_6\text{H}_5\text{CH}_2\text{NH}_2 \lt (\text{C}_2\text{H}_5)_2\text{NH} \)
The Correct Option is A
Solution and Explanation
• Basic strength of amines depends on the availability of the lone pair of electrons on the nitrogen atom.
• It is influenced by the +I (Inductive) effect, resonance effect, and steric hindrance.
• Alkyl groups increase basicity via +I effect, while aryl groups (phenyl) decrease it via resonance.
Step 1: Comparing Ammonia and Aniline
In Aniline \( (\text{C}_6\text{H}_5\text{NH}_2) \), the lone pair on nitrogen is delocalized into the benzene ring due to resonance.
This makes the lone pair less available for donation compared to Ammonia \( (\text{NH}_3) \).
Order: \( \text{C}_6\text{H}_5\text{NH}_2 \lt \text{NH}_3 \).
Step 2: Evaluating Benzylamine and Aliphatic Amines
In Benzylamine \( (\text{C}_6\text{H}_5\text{CH}_2\text{NH}_2) \), the nitrogen is not directly attached to the ring, so no resonance occurs.
The benzyl group has a weak electron-withdrawing effect compared to ethyl groups.
In Ethylamines \( (\text{C}_2\text{H}_5\text{NH}_2 \text{ and } (\text{C}_2\text{H}_5)_2\text{NH}) \), the +I effect of ethyl groups significantly increases electron density on nitrogen.
Step 3: Ordering the ethylamines in aqueous solution
For the ethyl group, the basicity order in aqueous solution is \( 2^\circ \gt 1^\circ \gt 3^\circ \gt \text{NH}_3 \).
Thus, \( (\text{C}_2\text{H}_5)_2\text{NH} \gt \text{C}_2\text{H}_5\text{NH}_2 \).
Step 4: Final assembly of the order
Combining all factors: Aniline (weakest) < Ammonia < Benzylamine < Ethylamine < Diethylamine (strongest).
This matches the sequence: \( \text{C}_6\text{H}_5\text{NH}_2 \lt \text{NH}_3 \lt \text{C}_6\text{H}_5\text{CH}_2\text{NH}_2 \lt \text{C}_2\text{H}_5\text{NH}_2 \lt (\text{C}_2\text{H}_5)_2\text{NH} \).
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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-methylanilineAccount 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.
(v) Aniline does not undergo Friedel-Crafts reaction.
(vi) Diazonium salts of aromatic amines are more stable than those of aliphatic amines. (vii) Gabriel phthalimide synthesis is preferred for synthesising primary amines.
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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-methylanilineAccount 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.
(v) Aniline does not undergo Friedel-Crafts reaction.
(vi) Diazonium salts of aromatic amines are more stable than those of aliphatic amines. (vii) Gabriel phthalimide synthesis is preferred for synthesising primary amines.
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 Exercises Rationalised 2023-24 279 Amines (b) C6H5NH2 , C6H5NHCH3 , C6H5CH2NH2 .
(iv) In decreasing order of basic strength in gas phase: C2H5NH2 , (C2H5 )2NH, (C2H5 )3N and NH3
(v) In increasing order of boiling point: C2H5OH, (CH3 )2NH, C2H5NH2
(vi) In increasing order of solubility in water: C6H5NH2 , (C2H5 )2NH, C2H5NH2 .
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?
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