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Amines & Diazonium Salts revision notes

Every idea in the Amines & Diazonium Salts chapter for JEE Main, with the usual mistakes and the fast methods. Topic 1 is open to everyone; sign in free to read all 23 and download the PDF.

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Structure, classification and physical properties

Structure and classification
3× asked, last 2024
R−NHX2 (1∘),RX2NH (2∘),RX3N (3∘),RX4NX+XX− (quaternary)\ce{R-NH2}\ (1^\circ),\qquad \ce{R2NH}\ (2^\circ),\qquad \ce{R3N}\ (3^\circ),\qquad \ce{R4N+X-}\ (\text{quaternary})
N is sp3sp^3 and pyramidal with one lone pair; C–N–C in (CHX3)X3N\ce{(CH3)3N} is 108°. Degree = number of C atoms on N.
N 2 H
tert-butylamine
1°: 1 C on N
N H
N-methylethanamine
2°: 2 C on N
N
N,N-dimethyl-
methanamine
3°: 3 C on N
N +
(CH₃)₄N⁺
quaternary: 4 C on N
  • IUPAC: alkane 'e' → 'amine' (ethanamine); the longest chain on N is the parent; other groups on N get locant N: (CHX3)X3N\ce{(CH3)3N} N,N-dimethylmethanamine, (CHX3)X2CHNHX2\ce{(CH3)2CHNH2} propan-2-amine. Diamines keep the 'e': hexane-1,6-diamine.
  • Not the alcohol rule. Degree counts C atoms on N, so (CHX3)X3C−NHX2\ce{(CH3)3C-NH2} is 1°. Propanamine (1°) and N-methylethanamine (2°) are functional isomers. Aniline, benzenamine and aminobenzene are one compound.
Physical properties
4× asked, last 2026
bp (K, M≈72–74): CX4HX9OH 390>CX4HX9NHX2 351>(CX2HX5)X2NH 329>CX2HX5N(CHX3)X2 311>CX2HX5CH(CHX3)X2 301\text{bp (K, } M\approx 72\text{–}74):\ \ce{C4H9OH}\ 390 > \ce{C4H9NH2}\ 351 > \ce{(C2H5)2NH}\ 329 > \ce{C2H5N(CH3)2}\ 311 > \ce{C2H5CH(CH3)2}\ 301
Similar mass. N–H···N bonds are weaker than O–H···O; 3° amines have no N–H. Arylamines darken in air (oxidation).
390C₄H₉OH351C₄H₉NH₂329(C₂H₅)₂NH311C₂H₅N(CH₃)₂301C₂H₅CH(CH₃)₂
b.p. in K (sheet); M 72–74 from the formulas; N–H on the structures 2 > 1 > 0
  • Lower aliphatic amines dissolve in water (H-bonds); solubility falls as the alkyl part grows; amines are less soluble than matching alcohols; aniline is sparingly soluble.
  • Not 'more N–H, weaker association'. 1° amines (two N–H) associate more than 2° (one N–H) and boil higher. o-Nitroaniline H-bonds inside the molecule, so like o-nitrophenol it is steam volatile.

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Practise Amines & Diazonium Salts

21 more concepts in 5 topics

Preparation of amines, Basic character of amines, Reactions at nitrogen and tests, Electrophilic substitution in aniline and Diazonium salts. Read the first part free. Sign in free with Google to read the rest and download the PDF.

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Preparation of amines

  • Reduction of nitro compounds5×
  • Ammonolysis and alkylation6×
  • Reduction of nitriles and amides16×
  • Gabriel phthalimide synthesis13×
  • Hofmann bromamide degradation21×

Basic character of amines

  • Basicity of aliphatic amines6×
  • Arylamines and amides: weak bases8×
  • Ring substituents and the ortho effect1×

Reactions at nitrogen and tests

  • Acylation and benzoylation6×
  • Carbylamine (isocyanide) test11×
  • Hinsberg test18×
  • Reaction with nitrous acid10×
  • Also remember1

Electrophilic substitution in aniline

  • Bromination and protecting –NH₂12×
  • Nitration: the anilinium ion7×
  • Sulphonation: sulphanilic acid2×
  • No Friedel–Crafts on aniline6×

Diazonium salts

  • Diazotisation and stability6×
  • Replacement by halogen, CN and NO₂13×
  • Replacement by OH and by H11×
  • Coupling: azo dyes22×
  • Diazonium route to hard patterns14×

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