Amines for NEET UG
Amines are organic derivatives of ammonia. Their basicity, the tests that tell primary, secondary and tertiary amines apart, and diazonium salts are the key topics.
ChemistryClass 1269 MCQs2 lessons14 flashcards3 memory tricks
What you'll learn
- Basicity of amines
Compare the basic strength of aliphatic amines, aniline and ammonia. - Tests and diazonium salts
Distinguish 1°, 2° and 3° amines, and use diazonium salts to make other compounds.
Key formulas
| In water (methyl amines) | (CH₃)₂NH > CH₃NH₂ > (CH₃)₃N > NH₃ |
|---|---|
| In water (ethyl amines) | (C₂H₅)₂NH > (C₂H₅)₃N > C₂H₅NH₂ > NH₃ |
| Aromatic vs aliphatic | Aliphatic amines > NH₃ > aniline |
Memory tricks
Ethylamines: 2° > 3° > 1° > NH₃. Methylamines: 2° > 1° > 3° > NH₃. Basicity is a balance of the +I effect, solvation and crowding.
Primary amines (aliphatic or aromatic) heated with CHCl₃ and alcoholic KOH give foul-smelling isocyanides. 2° and 3° amines don't.
Aniline + NaNO₂ + HCl at 0–5 °C gives benzenediazonium chloride, which couples with phenol to give an orange azo dye.
Try 3 NEET-style questions
Q1. Which amine is the strongest base in the gas phase?
- (CH₃)₂NH
- (CH₃)₃N
- CH₃NH₂
- NH₃
Show answer
Answer: (2) (CH₃)₃N
In the gas phase, there is no solvation, so the +I effect dominates: 3° > 2° > 1° > NH₃.
Q2. The arrangement of the three methyl groups around nitrogen in trimethylamine is
- trigonal planar
- linear
- pyramidal
- square planar
Show answer
Answer: (3) pyramidal
N is sp³ hybridised with three bond pairs and one lone pair, so the molecule is pyramidal (C–N–C angle about 108°).
Q3. In ammonolysis of an alkyl halide, a primary amine can be obtained as the major product by
- using excess alkyl halide
- adding water
- using a large excess of ammonia
- heating without ammonia
Show answer
Answer: (3) using a large excess of ammonia
Ammonolysis gives a mixture of 1°, 2°, 3° amines and quaternary salts. Using a large excess of ammonia favours the primary amine.
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