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Amines and Diazonium Salts: one-page cheat sheet

NEET Chemistry · Unit 18 · Organic Chemistry

ScoreChemby CSJ Sir
Weightage: 2–3 questions · 8–12 marks

1 · Structure & naming

ShapeN is

s p^{3}

, pyramidal; C–N–C about

10 8^{\circ}

in Me

_{3}

Classes

1^{\circ}

RNH

_{2}

;

2^{\circ}

_{2}

NH;

3^{\circ}

_{3}

N; quaternary R

_{4}

^{+}

^{-}

IUPACalkanamine;

N

-methylethanamine;

N, N

-dimethylaniline

2 · Preparation

NitroFe / HCl, Sn / HCl or H

_{2}

/ Pd: ArNO

_{2}

\to

ArNH

_{2}

NitrileLiAlH

_{4}

or Na(Hg) / EtOH: R–CN

\to

RCH

_{2}

_{2}

(one C more)

AmideLiAlH

_{4}

: RCONH

_{2}

\to

RCH

_{2}

_{2}

(same C)

IsocyanideLiAlH

_{4}

: RNC

\to

secondary RNHCH

_{3}

AmmonolysisRX + NH

_{3}

gives a mixture of

1^{\circ}

2^{\circ}

3^{\circ}

and quaternary salts

Gabrielpotassium phthalimide + R–X: pure

1^{\circ}

aliphatic only; not aniline

RCONH_{2} + Br_{2} + 4 NaOH \to RNH_{2} + Na_{2} CO_{3} + 2 NaBr + 2 H_{2} O

Hofmann bromamide: one carbon less.

3 · Basicity

b.p.

1^{\circ} > 2^{\circ} > 3^{\circ}

(N–H hydrogen bonds)

Gas phase

3^{\circ} > 2^{\circ} > 1^{\circ} > NH_{3}

(

+ I

)

Water, ethyl

2^{\circ} > 3^{\circ} > 1^{\circ} > NH_{3}

Water, methyl

2^{\circ} > 1^{\circ} > 3^{\circ} > NH_{3}

K_{b}

_{3}

4.75; aniline 9.38 (lone pair delocalised)

Donor groups (CH $_{3}$ , OCH $_{3}$ ) raise basicity of aniline; NO $_{2}$ , CN, halogens lower it.

4 · Reactions & tests

Acylation

1^{\circ}

2^{\circ}

+ RCOCl (pyridine)

\to

amide;

3^{\circ}

Carbylamine

1^{\circ}

only: CHCl

_{3}

+ alc. KOH gives foul RNC

Hinsberg (PhSO $_{2}$ Cl)	Result
$1^{\circ}$	sulphonamide, dissolves in KOH
$2^{\circ}$	insoluble in KOH
$3^{\circ}$	no reaction

HNO

_{2}

1^{\circ}

aliphaticROH + N

_{2}

(quantitative)

HNO

_{2}

1^{\circ}

aromaticdiazonium salt at 273–278 K

HNO

_{2}

2^{\circ}

yellow oily nitrosamine

5 · Aniline: ring reactions

_{2}

waterwhite 2,4,6-tribromoaniline at once

Mono-bromoprotect: acetylate with (CH

_{3}

CO)

_{2}

O first

Nitration51% para, 47% meta, 2% ortho (anilinium is meta-directing)

Sulphonation453–473 K: sulphanilic acid (zwitterion)

Friedel–Craftsfails: NH

_{2}

binds AlCl

_{3}

6 · Diazonium salts

FormationArNH

_{2}

+ NaNO

_{2}

+ HCl, 273–278 K; explosive when dry

Reagent	Product
Cu $_{2}$ X $_{2}$ / HX (Sandmeyer), Cu / HX (Gattermann)	ArCl, ArBr, ArCN
KI (no copper)	ArI
HBF $_{4}$ , then heat (Balz–Schiemann)	ArF
H $_{3}$ PO $_{2}$	ArH (deamination)
H $_{2}$ O, warm above 283 K	ArOH

7 · Azo coupling

With phenolpH 9–10:

p

-hydroxyazobenzene (orange)

With anilinepH 4–5:

p

-aminoazobenzene (yellow)

8 · Why arenediazonium is stable

Reason

π

-electrons of the ring delocalise the N

_{2}^{+}

charge by resonance

Alkylalkyldiazonium ions decompose at once (to ROH, alkenes, RX)

Useazo dyes; dry salts explode, so use in solution

Seen in NEET 2024

CH $_{3}$ CH $_{2}$ CH $_{2}$ I, NaCN, partial hydrolysis, Br $_{2}$ / NaOH.

C_{3} H_{7} I \to C_{3} H_{7} CN \to C_{3} H_{7} CONH_{2} \to C_{3} H_{7} NH_{2}

Propan-1-amine: one carbon is lost in the Hofmann step.

Seen in NEET 2026

C $_{2}$ H $_{5}$ Cl + AgCN gives C $_{2}$ H $_{5}$ NC.

Propanamide gives ethanamine (Hofmann); with CHCl $_{3}$ / KOH it gives the same isocyanide.

Seen in NEET 2020, 2021

Carbylamine positive: aniline, a $1^{\circ}$ amine.

Hinsberg product soluble in KOH: ethylamine, CH $_{3}$ CH $_{2}$ NH $_{2}$ .

Six traps to remember

The Hofmann bromamide product has one carbon less than the amide.
Gabriel synthesis cannot make aniline (aryl halides resist S $_{N}$ ).
In water the order is $2^{\circ} > 3^{\circ}$ for ethylamines but $2^{\circ} > 1^{\circ} > 3^{\circ}$ for methylamines.
Only primary amines give the carbylamine test.
Aniline fails Friedel–Crafts; it forms a salt with AlCl $_{3}$ .
Diazonium salts are kept at 273–278 K; warming gives phenol.

Amines and Diazonium Salts: free one-page cheat sheet