0Class 12 Chemistry – Amines
1. Introduction
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Amines are organic compounds in which one or more hydrogen atoms of ammonia (NH₃) are replaced by alkyl or aryl groups.
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They are derivatives of ammonia and are classified based on how many hydrogens are replaced.
2. Classification of Amines
a) Primary Amines (1°)
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One hydrogen of ammonia is replaced by an alkyl or aryl group.
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Structure concept: R–NH₂
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Example: Methylamine
b) Secondary Amines (2°)
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Two hydrogens replaced by alkyl or aryl groups.
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Structure concept: R–NH–R’
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Example: Dimethylamine
c) Tertiary Amines (3°)
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All three hydrogens replaced by alkyl or aryl groups.
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Structure concept: R–N–R’R’’
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Example: Trimethylamine
3. Physical Properties
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State: Low molecular weight amines are gaseous or liquids; higher ones are liquids or solids.
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Odor: Have a fishy smell.
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Solubility: Small amines are soluble in water due to hydrogen bonding.
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Boiling Point: Lower than alcohols of similar mass, increases with hydrogen bonding.
4. Chemical Properties
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Basic Nature: Amines are basic because of the lone pair of electrons on nitrogen.
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Reactions with acids: Form salts when reacted with acids.
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Acylation: Can react with acid derivatives to form amides.
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Alkylation: Can react to form higher amines.
5. Aromatic Amines
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Example: Aniline (C₆H₅–NH₂)
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Amines attached to aromatic rings have different reactivity due to the resonance effect of the ring.
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They are less basic than aliphatic amines because the lone pair on nitrogen is partially delocalized into the ring.
6. Applications
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Aliphatic amines: Used in dyes, pharmaceuticals, and synthetic intermediates.
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Aromatic amines: Used in dye industries, drugs, and polymers.
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Basic nature: Useful in neutralizing acids and preparing salts.
7. Key Points to Remember
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Amines are derivatives of ammonia, classified as primary, secondary, and tertiary.
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Basicity: Aliphatic amines are more basic than aromatic amines.
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Solubility and odor: Small amines are soluble and have a fishy smell.
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Aromatic amines are less reactive due to resonance stabilization.
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Important in chemical industries, pharmaceuticals, and synthetic organic chemistry.
