Chemistry
Organic Compounds Containing Nitrogen
Nitrogen Compounds Formula Sheet
All key Chemistry reactions, basicity orders, and named reactions for amines and diazonium salts - JEE Main & Advanced quick revision in one place.
This is a mostly descriptive organic chapter, so the sheet is built around named reactions, reagent-product maps, and basicity orders rather than numeric formulas. Every reaction and order below is taken directly from the chapter pages.
How to use this sheet
The high-value JEE items here are the aqueous basicity order, the HNO₂ test products, and the diazonium reagent-to-product map. Lock those three down first.
Classification at a Glance
| Type | General formula | Note |
|---|---|---|
| Primary (1°) | $\text{R-NH}_2$ | One group on N |
| Secondary (2°) | $\text{R}_2\text{NH}$ | Two groups on N |
| Tertiary (3°) | $\text{R}_3\text{N}$ | Three groups on N |
| Quaternary salt | $\text{R}_4\text{N}^+\text{X}^-$ | NOT an amine (no lone pair, not basic) |
- Aromatic amine: N directly on ring, e.g. aniline $\text{C}_6\text{H}_5\text{-NH}_2$.
- Aliphatic (even with a ring): N on CH₂, e.g. benzylamine $\text{C}_6\text{H}_5\text{-CH}_2\text{-NH}_2$.
- Structure of N in amines: sp³, pyramidal, bond angle ~107°, one lone pair.
Basicity (High-Yield)
Defining relations
$$\text{R-NH}_2 + \text{H}_2\text{O} \rightleftharpoons \text{R-NH}_3^+ + \text{OH}^-$$$$K_b = \frac{[\text{R-NH}_3^+][\text{OH}^-]}{[\text{R-NH}_2]}, \qquad \text{p}K_b = -\log K_b$$$$\boxed{K_a \times K_b = K_w = 10^{-14}}$$$$\boxed{\text{p}K_a + \text{p}K_b = 14}$$- Lower $\text{p}K_b$ → stronger base; higher $\text{p}K_a$ of conjugate acid → stronger base.
Order of basicity
$$\boxed{\text{Aqueous: } 2° > 1° > 3° > \text{NH}_3}$$$$\boxed{\text{Gas phase: } 3° > 2° > 1° > \text{NH}_3}$$- Aqueous winner is set by a balance of +I effect (3° > 2° > 1°) and solvation of conjugate acid (1° > 2° > 3°).
- Gas phase is controlled by +I effect alone.
The chapter’s “ultimate JEE order”:
$$(\text{CH}_3)_2\text{NH} > \text{CH}_3\text{NH}_2 > \text{C}_6\text{H}_5\text{CH}_2\text{NH}_2 > \text{NH}_3 > \text{C}_6\text{H}_5\text{NH}_2$$Substituent effect on aniline
$$\text{p-CH}_3\text{O-C}_6\text{H}_4\text{-NH}_2 > \text{p-CH}_3\text{-C}_6\text{H}_4\text{-NH}_2 > \text{C}_6\text{H}_5\text{-NH}_2 > \text{p-Cl-C}_6\text{H}_4\text{-NH}_2 > \text{p-NO}_2\text{-C}_6\text{H}_4\text{-NH}_2$$- EDG (−OCH₃, −CH₃, −NH₂) increase basicity; EWG (−NO₂, −CN, −X, −CHO) decrease it.
- Nitroaniline isomers: meta > para > ortho (meta has no direct resonance with NH₂, so only −I acts).
pKb values to remember
| Amine | pKb |
|---|---|
| $(\text{CH}_3)_2\text{NH}$ | 3.27 (strongest aliphatic) |
| $\text{CH}_3\text{NH}_2$ | 3.38 |
| $\text{C}_2\text{H}_5\text{NH}_2$ | 3.35 |
| $(\text{CH}_3)_3\text{N}$ | 4.22 |
| $\text{NH}_3$ | 4.75 (reference) |
| $\text{C}_6\text{H}_5\text{CH}_2\text{NH}_2$ | 4.70 |
| $\text{C}_6\text{H}_5\text{NH}_2$ (aniline) | 9.42 |
| m-nitroaniline | 11.5 |
| p-nitroaniline | 13.0 |
| o-nitroaniline | 14.3 |
Special cases
| Species | Behaviour | Reason |
|---|---|---|
| Guanidine | Extremely strong base, pKb ≈ 0.4 | Conjugate acid: +ve charge over 3 equivalent N (resonance) |
| Pyrrole | Essentially non-basic, pKb > 14 | N lone pair is part of aromatic sextet |
| Aniline > diphenylamine > triphenylamine | Decreasing basicity | More phenyls → more lone-pair delocalization |
Preparation of Amines
| Starting material | Reagent | Product | Carbon change |
|---|---|---|---|
| $\text{R-NO}_2$ | Sn/HCl, Fe/HCl, LiAlH₄, or H₂/Ni | 1° amine | none |
| $\text{R-CN}$ | LiAlH₄, H₂/Ni, or Na/C₂H₅OH | 1° amine | +1 |
| $\text{R-CO-NH}_2$ | LiAlH₄ | 1° amine | none |
| $\text{R-CO-NH}_2$ | Br₂ + 4 NaOH (Hoffmann) | 1° amine | −1 |
| Phthalimide | (1) KOH (2) R-X (3) H₃O⁺ (Gabriel) | pure 1° aliphatic | none |
| $\text{NH}_3$ | R-X | mixture of 1°,2°,3°,quaternary | none |
| $\text{R-CHO} + \text{R'-NH}_2$ | then [H] (reductive amination) | 2° amine | varies |
Key headline equations:
$$\boxed{\text{R-NO}_2 + 6[\text{H}] \rightarrow \text{R-NH}_2 + 2\text{H}_2\text{O}}$$$$\boxed{\text{R-CN} + 4[\text{H}] \rightarrow \text{R-CH}_2\text{-NH}_2}$$$$\boxed{\text{R-CO-NH}_2 \xrightarrow{\text{LiAlH}_4} \text{R-CH}_2\text{-NH}_2}$$$$\boxed{\text{R-CO-NH}_2 + \text{Br}_2 + 4\text{NaOH} \rightarrow \text{R-NH}_2 + \text{Na}_2\text{CO}_3 + 2\text{NaBr} + 2\text{H}_2\text{O}}$$
LiAlH₄ vs Hoffmann on an amide
Same amide, two different amines: $\text{C}_6\text{H}_5\text{CONH}_2 \xrightarrow{\text{LiAlH}_4} \text{C}_6\text{H}_5\text{CH}_2\text{NH}_2$ (benzylamine, all C kept) vs $\text{C}_6\text{H}_5\text{CONH}_2 \xrightarrow{\text{Br}_2/\text{NaOH}} \text{C}_6\text{H}_5\text{NH}_2$ (aniline, one C lost). “LiAlH₄ is Loyal, Hoffmann is Harsh.”
- Amide reduction preserves degree: 1° amide → 1° amine, 2° amide → 2° amine, 3° amide → 3° amine.
- Gabriel fails for aromatic amines (aryl halides don’t do SN2). For aniline, reduce nitrobenzene instead.
- Selective reduction of one −NO₂ in m-dinitrobenzene: use (NH₄)₂S.
Physical Properties
$$\boxed{\text{Boiling point (similar mass): } 1° > 2° > 3°}$$$$\boxed{\text{Alcohols} > \text{1° Amines} > \text{Hydrocarbons (similar mass)}}$$- Driver: H-bonding capacity (count of N-H bonds). H-bonding outweighs molecular mass — e.g. $(\text{CH}_3)_2\text{NH}$ (bp 7°C) > $(\text{CH}_3)_3\text{N}$ (bp 3°C) despite higher mass of the 3° amine.
- Solubility in water: lower amines C₁-C₄ soluble; aromatic amines insoluble (but soluble in dilute acid as the salt). Order $1° \approx 2° > 3°$.
Chemical Reactions of Amines
Salt formation, acylation, benzoylation
$$\text{R-NH}_2 + \text{HCl} \rightarrow [\text{R-NH}_3^+]\text{Cl}^-$$$$\text{R-NH}_2 + \text{CH}_3\text{COCl} \rightarrow \text{R-NH-CO-CH}_3 + \text{HCl}$$$$\text{R-NH}_2 + \text{C}_6\text{H}_5\text{COCl} \xrightarrow{\text{NaOH}} \text{R-NH-CO-C}_6\text{H}_5 \quad (\text{Schotten-Baumann})$$- Acylation/benzoylation: 1° and 2° react; 3° does not (no N-H).
Identification tests
| Test | Reagent | 1° | 2° | 3° |
|---|---|---|---|---|
| Carbylamine | CHCl₃ + 3KOH, Δ | foul-smelling isocyanide (positive) | no reaction | no reaction |
| Hinsberg | C₆H₅SO₂Cl | sulfonamide, soluble in KOH | sulfonamide, insoluble | no reaction |
Carbylamine scope
Carbylamine distinguishes 1° from 2°/3°, NOT aliphatic from aromatic. Both aliphatic and aromatic primary amines give the foul smell.
Reaction with nitrous acid (HNO₂)
| Amine | Product | Observation |
|---|---|---|
| 1° aliphatic | R-OH + N₂ | brisk effervescence (N₂ gas) |
| 1° aromatic | $[\text{Ar-N}_2^+]\text{Cl}^-$ | stable diazonium salt at 0-5°C |
| 2° (aliphatic or aromatic) | $\text{R}_2\text{N-N=O}$ | yellow oily N-nitrosamine (carcinogenic) |
| 3° aliphatic | $[\text{R}_3\text{NH}^+]\text{NO}_2^-$ | water-soluble nitrite salt |
| 3° aromatic | p-nitroso-N,N-dialkylaniline | green colour |
Electrophilic substitution in aniline
- −NH₂ is strongly activating, ortho/para directing; electron density ortho ≈ para > meta.
- Direct bromination gives 2,4,6-tribromoaniline (white ppt) — uncontrolled.
- For mono-substitution: acetylate → react → hydrolyse (acetanilide is moderately activating).
- Sulphonation of aniline (via anilinium salt, 180-200°C) gives sulfanilic acid (p-aminobenzenesulfonic acid).
- Oxidation: aniline → black tar (cannot be cleanly oxidised to nitrobenzene).
Diazonium Salts
Diazotization
$$\boxed{\text{Ar-NH}_2 + \text{NaNO}_2 + 2\text{HCl} \xrightarrow{0\text{-}5°\text{C}} [\text{Ar-N}_2^+]\text{Cl}^- + \text{NaCl} + 2\text{H}_2\text{O}}$$- Aromatic 1° amines only; 0-5°C essential; never isolate, use in situ.
- Above ~10°C decomposes: $[\text{C}_6\text{H}_5\text{N}_2^+]\text{Cl}^- \rightarrow \text{C}_6\text{H}_5\text{OH} + \text{N}_2 + \text{HCl}$.
- Aromatic salts are stable (resonance with ring); aliphatic salts decompose instantly even at 0°C.
Replacement reactions (memorize this map)
| Target group | Reagent | Named method | Product |
|---|---|---|---|
| −F | HBF₄, then heat | Balz-Schiemann | Ar-F |
| −Cl | CuCl, or Cu/HCl | Sandmeyer / Gattermann | Ar-Cl |
| −Br | CuBr, or Cu/HBr | Sandmeyer / Gattermann | Ar-Br |
| −I | KI (no catalyst) | direct substitution | Ar-I |
| −CN | CuCN | Sandmeyer only | Ar-CN |
| −OH | H₂O, warm | hydrolysis | phenol |
| −H | H₃PO₂ or C₂H₅OH/Zn | reduction (deamination) | arene |
| −N=N-Ar′ | Ar′-OH or Ar′-NR₂ | coupling | azo dye |
- For −CN only Sandmeyer (CuCN) works; for −F only Balz-Schiemann; for −I plain KI suffices.
- Synthetic chains: aniline → ArN₂⁺ → CuCN → Ar-CN → (H₃O⁺) → Ar-COOH; aniline → ArN₂⁺ → (H₂O, warm) → phenol.
Azo Coupling and Dyes
$$\boxed{[\text{Ar-N}_2^+]\text{X}^- + \text{Ar'-H} \rightarrow \text{Ar-N=N-Ar'} + \text{HX}}$$| Coupling partner | pH / medium | Reason |
|---|---|---|
| Phenols, naphthols | pH 8-10 (alkaline) | forms phenoxide (C₆H₅O⁻), more activated |
| Aromatic amines | pH 4-5 (weakly acidic) | keeps −NH₂ free and N₂⁺ stable |
- Coupling needs a strongly activated ring (−OH, −OR, −NH₂, −NHR, −NR₂). Benzene, toluene, chlorobenzene, nitrobenzene do not couple.
- Regioselectivity: predominantly para (less steric hindrance). Temperature 0-5°C throughout.
- Colour source: extended conjugation; chromophore = −N=N−; auxochromes = −OH, −NH₂, −SO₃H. EDG → bathochromic (red) shift; EWG → hypsochromic (blue) shift.
- Methyl orange = sulfanilic acid (diazotized) + N,N-dimethylaniline; red in acid (pH < 3.1), yellow in base (pH > 4.4).
- Orange II = sulfanilic acid (diazotized) + β-naphthol (alkaline coupling).
Classic identification test
An unknown gives a diazonium salt with NaNO₂/HCl at 0-5°C and then a brilliant orange dye with alkaline β-naphthol → the unknown is an aromatic primary amine (e.g. aniline).
Reaction Map
graph TD
NB["Nitrobenzene C6H5NO2"] -->|Sn/HCl| AN["Aniline C6H5NH2"]
AN -->|"NaNO2/HCl, 0-5C"| DZ["Diazonium C6H5N2+ Cl-"]
DZ -->|CuCl| ArCl["Chlorobenzene"]
DZ -->|CuCN| ArCN["Benzonitrile"]
DZ -->|"H2O, warm"| PhOH["Phenol"]
DZ -->|H3PO2| Bz["Benzene"]
DZ -->|"HBF4, heat"| ArF["Fluorobenzene"]
DZ -->|KI| ArI["Iodobenzene"]
DZ -->|"phenol/amine coupling"| Azo["Azo dye Ar-N=N-Ar'"]
ArCN -->|H3O+| COOH["Benzoic acid"]