Amines – NEET Chemistry Class 12

Amines are organic compounds containing nitrogen with a lone pair, typically in the form –NH₂, –NHR, or –NR₂. This chapter is crucial for NEET as it covers classification, basicity, reactions, and electrophilic substitution in aromatic amines.

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Introduction to Amines

• Definition: Organic derivatives of ammonia (NH₃) in which one or more hydrogen atoms are replaced by alkyl or aryl groups.

• General Formula:

  • Primary amine (1°): R–NH₂

  • Secondary amine (2°): R–NH–R’

  • Tertiary amine (3°): R–N–R’₂

• Importance: Amines are widely used in dyes, pharmaceuticals, and agrochemicals and frequently appear in NEET questions.

Nomenclature

• IUPAC Names: Based on longest carbon chain attached to nitrogen:

  • Primary amines: Suffix –amine (e.g., Ethanamine)

  • Secondary/tertiary amines: N-substituted (e.g., N-Methylethanamine)

• Common Names: Used for simpler amines (e.g., Methylamine, Dimethylamine)

Classification

1. Based on Structure:

   • Aliphatic amines: R–NH₂, R–NHR’, R–NR’₂

   • Aromatic amines: Ar–NH₂ (e.g., Aniline)

2. Based on Substitution:

   • Primary (1°), Secondary (2°), Tertiary (3°)

3. Cyclic Amines: Nitrogen incorporated in rings (e.g., Piperidine)

Physical Properties

• Small amines are soluble in water due to hydrogen bonding

• Higher amines have lower solubility due to increasing nonpolar alkyl chains

• Boiling points: Primary > Secondary > Tertiary amines (except H-bonding exceptions)

• Aromatic amines like aniline show weaker H-bonding due to delocalization of nitrogen lone pair

Chemical Properties

1. Basicity:

   • Lone pair on nitrogen accepts a proton → basic behavior

   • Aliphatic amines > Aromatic amines (aniline less basic due to resonance)

2. Reactions with Nitrous Acid (HNO₂):

   • Primary aliphatic amines → Alcohols (via diazonium intermediates)

   • Primary aromatic amines → Diazonium salts (important in dye chemistry)

3. Acylation and Alkylation:

   • Acylation forms amides

   • Alkylation can lead to over-alkylation forming tertiary amines

4. Electrophilic Substitution in Aromatic Amines:

   • Amino group is activating and ortho/para directing

   • Examples: Nitration of aniline, halogenation

Importance for NEET Preparation

• Questions often involve basicity, reaction with nitrous acid, acylation, and aromatic substitution.

• Amines appear in organic reaction mechanisms and industrial applications, making them high-yield for NEET.

• Understanding structure-reactivity relationship is crucial for solving NEET questions efficiently.

Previous Year NEET Questions – Insights

• Comparing basicity of aliphatic vs aromatic amines

• Formation and reactions of diazonium salts

• Electrophilic substitution reactions (e.g., nitration, halogenation)

• Reactions with acyl halides forming amides

• Alkylation reactions of primary amines

Study Tips for Students

1. Memorize Nomenclature Rules – Primary, secondary, tertiary, aromatic amines

2. Practice Mechanisms – Diazotization, electrophilic substitution, acylation

3. Understand Physical Properties and Basicity Trends – Compare aliphatic vs aromatic amines

4. Refer NCERT Examples – NEET follows NCERT closely

5. Solve Previous Year Questions – Reinforces reaction mechanisms and product predictions

Conclusion

Mastering Amines is essential for NEET success. It allows students to predict reaction outcomes, understand basicity trends, and solve mechanism-based questions confidently. A strong understanding ensures high scoring potential in Class 12 organic chemistry.