Subtopics - Nitrogen Containing Compounds (NEET)
Nitro compounds, cyanides, amines, basicity, diazonium chemistry, and azo dyes
1) Nitro Compounds and Their Reduction
Alkyl nitrites (R-ONO) vs nitroalkanes (R-NO2): tautomeric relationship, distinction by boiling points and NaOH hydrolysis. Nitroalkane preparation from alkyl halides (mixture of RCN + RNC with KCN; pure RNO2 with AgNO2). Aromatic nitro compounds: nitration conditions (HNO3/H2SO4), temperature/concentration control for mono/di/trinitration. Reduction: acidic medium (Sn/HCl gives amine), neutral medium (Zn/NH4Cl gives hydroxylamine or nitrosobenzene), alkaline medium (Zn/NaOH gives azoxybenzene, azobenzene, hydrazobenzene). Selective reduction of one NO2 in dinitrobenzene using (NH4)2S.
2) Cyanides and Isocyanides
Alkyl cyanides (R-CN): prepared from RX + KCN (major product), dehydration of amides (P2O5), Grignard + ClCN. Hydrolysis gives carboxylic acid. Reduction (LiAlH4 or Na/alcohol) gives primary amine. Alkyl isocyanides (R-NC): prepared from RX + AgCN (major) or carbylamine reaction (R-NH2 + CHCl3/KOH). Hydrolysis gives primary amine + formic acid. The carbylamine test is the key identification reaction for primary amines (foul smell of isocyanide).
3) Amine Basicity and Chemical Properties
Basicity of aliphatic amines: inductive effect predicts 3 degree > 2 degree > 1 degree > NH3, but solvation of cation reverses 2 degree and 3 degree in water (actual: 2 degree > 1 degree > 3 degree for ethylamines). In non-H-bonding solvent (chlorobenzene): 3 degree > 2 degree > 1 degree as expected. Aromatic amines: aniline weaker than NH3 due to resonance delocalisation of N lone pair into ring. EWG (NO2 at o/p) further weakens basicity; EDG (OCH3 at p) strengthens it. Chemical properties: salt formation with acids, alkylation (exhaustive methylation gives quaternary salt, Hofmann elimination), acylation (acetylation protects NH2 for controlled electrophilic substitution), Hinsberg test (benzenesulfonyl chloride separates 1/2/3 degree amines).
4) Diazonium Salts and Coupling Reactions
Diazotisation: ArNH2 + NaNO2 + HCl at 0-5 degrees gives ArN2+Cl-. Aliphatic diazonium salts are unstable (decompose to mixture of ROH, RCl, alkene). Aromatic diazonium salts are stable at 0-5 degrees and serve as synthetic intermediates. Substitution reactions: boiling with H2O gives ArOH, Sandmeyer (CuCl/CuBr) gives ArCl/ArBr, Gattermann (Cu powder) gives ArCl/ArBr, Schiemann (HBF4) gives ArF, KI gives ArI, CuCN/KCN gives ArCN. Reduction: H3PO2 gives ArH. Coupling with phenol (alkaline) gives azo dye at para-position; coupling with aniline (weakly acidic) gives aminoazo compound. Azo dyes are coloured due to extended conjugation through N=N.
Nitrogen Containing Compounds Download Notes & Weightage Plan
For each topic in the Nitrogen Containing Compounds chapter below, you get (2) the exact resources to download and how to use them, and (3) a simple importance & time plan so NEET students know what to do first and what to revise last.
Nitro Compounds and Their Reduction
Nitrite vs nitroalkane, aromatic nitration, reduction in different media.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: Reduction product in different media is a classic NEET question. Know which medium gives which product.
- High-risk Area: Students confuse neutral and alkaline reduction products. Neutral (Zn/NH4Cl) gives phenylhydroxylamine; alkaline (Zn/NaOH) gives azoxybenzene.
- Best Practice Style: Make a 3-column table: acidic/neutral/alkaline media with reagent and product.
KCN vs AgCN selectivity, hydrolysis, carbylamine test.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: Carbylamine test for primary amines is directly tested. KCN vs AgCN product distinction is common.
- High-risk Area: Students forget that KCN gives cyanide (bond through C) while AgCN gives isocyanide (bond through N).
- Best Practice Style: Write both reactions with the same alkyl halide and compare products.
Amine Basicity and Chemical Properties
Basicity order, solvation anomaly, Hinsberg test, acetylation protection.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: Basicity comparison is the most tested topic. The water vs gas phase anomaly is a favourite conceptual question.
- High-risk Area: Students apply gas-phase order (pure inductive) in aqueous solution questions. In water, 2 degree > 1 degree > 3 degree for small alkylamines.
- Best Practice Style: Solve 10 basicity comparison MCQs covering both aliphatic and aromatic amines.
Diazonium Salts and Coupling Reactions
Diazotisation, Sandmeyer, Gattermann, Schiemann, azo coupling.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: Sandmeyer and Schiemann reactions are directly tested. Azo coupling with phenol is a common question.
- High-risk Area: Students confuse Sandmeyer (uses CuX) with Gattermann (uses Cu powder). Both give ArX but reagents differ.
- Best Practice Style: Write all diazonium reactions from memory as a single page summary.
Nitrogen Containing Compounds Chapter NEET Traps & Common Mistakes (Topic-Wise)
Each subtopic below is of the Nitrogen Containing Compounds chapter and shows what NEET students usually do wrong in NEET examination, a short example of the mistake, and how NEET frames the question to trick you with close options are given below.
Mistake Snapshot (What Students Do Wrong)
- Applying gas-phase order in aqueous solution: In gas phase: 3 degree > 2 degree > 1 degree > NH3 (pure inductive effect). In water: 2 degree > 1 degree > 3 degree > NH3 for ethylamines because tertiary ammonium cation has fewer N-H bonds for solvation (stabilisation by hydrogen bonding with water is reduced).
- Thinking the order is universal: The specific order depends on the alkyl group. For methylamines the order may differ from ethylamines. Always specify which amine series.
In water: Et2NH (pKa 11.09) > EtNH2 (pKa 10.75) > Et3N (pKa 10.78). In chlorobenzene: Bu3N > Bu2NH > BuNH2 (no solvation, pure inductive).
How NEET Frames The Trap
NEET asks for the correct basicity order of ethylamines in aqueous solution. Students who memorise only the inductive effect order get it wrong.
Q. The correct order of basicity of ethylamines in aqueous solution is:
A. Et3N > Et2NH > EtNH2 > NH3 B. Et2NH > Et3N > EtNH2 > NH3 C. Et2NH > EtNH2 > Et3N > NH3 D. EtNH2 > Et2NH > Et3N > NH3
Trick: Et2NH > EtNH2 > Et3N > NH3 because in water, diethylamine cation (Et2NH2+) has good balance of inductive stabilisation and solvation. Triethylamine cation (Et3NH+) has only one N-H for solvation, reducing its stability despite stronger inductive effect.
Mistake Snapshot (What Students Do Wrong)
- Confusing the reagents: Sandmeyer uses CuX (cuprous halide) in solution. Gattermann uses Cu powder (metallic copper). Both convert ArN2+ to ArX, but the catalyst form differs.
- Thinking they give different products: Both Sandmeyer and Gattermann give the same product (ArCl or ArBr). The difference is only in the reagent used. NEET asks specifically which reagent is used in which named reaction.
Sandmeyer: C6H5N2+Cl- + CuCl/HCl gives C6H5Cl. Gattermann: C6H5N2+Cl- + Cu powder/HCl gives C6H5Cl. Same product, different reagents.
How NEET Frames The Trap
A question names one reaction but describes the reagent of the other. Students must match the correct name to the correct reagent.
Q. In the Sandmeyer reaction, the diazonium salt is treated with:
A. Cu powder and HCl B. CuCl or CuBr in HCl C. NaCl in water D. HBF4
Trick: CuCl or CuBr in HCl is the Sandmeyer reagent. Cu powder (without halide salt) is the Gattermann reagent. HBF4 is the Schiemann reaction.
Mistake Snapshot (What Students Do Wrong)
- Confusing neutral and alkaline products: Neutral medium (Zn/NH4Cl) gives phenylhydroxylamine (PhNHOH). Alkaline medium (Zn/NaOH) gives bimolecular products: azoxybenzene, then azobenzene, then hydrazobenzene. Students swap these two.
- Forgetting the phenylhydroxylamine rearrangement: In strongly acidic electrolytic reduction, phenylhydroxylamine rearranges to p-aminophenol. This is a specific product from specific conditions.
Nitrobenzene + Sn/HCl gives aniline. Nitrobenzene + Zn/NH4Cl gives phenylhydroxylamine. Nitrobenzene + Zn/NaOH gives azoxybenzene.
How NEET Frames The Trap
NEET specifies a particular reducing agent and medium, then asks for the product. The answer depends entirely on whether the medium is acidic, neutral, or alkaline.
Q. When nitrobenzene is reduced with Zn dust and NH4Cl, the product is:
A. Aniline B. Phenylhydroxylamine C. Azoxybenzene D. Azobenzene
Trick: Phenylhydroxylamine because Zn/NH4Cl is a neutral reducing agent that performs a partial reduction, stopping at the hydroxylamine stage rather than going all the way to the amine.
Mistake Snapshot (What Students Do Wrong)
- Not accounting for resonance stabilisation of aniline: Aniline (pKa 4.62) is a much weaker base than cyclohexylamine (pKa 10.68) despite both having NH2 on a six-membered ring. In aniline, the nitrogen lone pair delocalises into the aromatic ring, making it less available for protonation.
- Thinking substituents always strengthen/weaken uniformly: p-NO2 group weakens basicity further (pKa 0.95) via resonance withdrawal. p-OCH3 strengthens slightly (pKa 5.29) via resonance donation. But o-substituents show anomalous behaviour due to steric effects.
Cyclohexylamine pKa = 10.68 (no resonance, inductive effect only). Aniline pKa = 4.62 (resonance of N lone pair with benzene ring). p-Nitroaniline pKa = 0.95 (extra resonance withdrawal).
How NEET Frames The Trap
A question asks which is more basic: aniline or cyclohexylamine. Students who see both have NH2 on C6 ring choose 'equal' or 'aniline' based on ring electron density.
Q. Aniline is a weaker base than cyclohexylamine because:
A. Aniline has a larger molecular size B. The lone pair on N in aniline is delocalised into the benzene ring C. Cyclohexylamine has more hydrogen bonding ability D. Aniline forms a more stable cation
Trick: The lone pair on N in aniline is delocalised into the benzene ring, making it less available for protonation. In cyclohexylamine, no such resonance exists and the lone pair is fully localised on nitrogen.
Mistake Snapshot (What Students Do Wrong)
- Applying carbylamine to secondary/tertiary amines: Only primary amines (RNH2) give the carbylamine test. Secondary amines (R2NH) and tertiary amines (R3N) do not react with CHCl3/KOH to form isocyanides.
- Confusing with other amine tests: Hinsberg test distinguishes all three classes. Carbylamine test detects only primary amines. Nitrous acid (HNO2) gives different products for 1/2/3 degree amines but is not as specific.
CH3NH2 + CHCl3 + 3KOH gives CH3NC (foul smell). (CH3)2NH + CHCl3 + KOH gives no isocyanide.
How NEET Frames The Trap
A question states that an amine gives a foul-smelling compound with CHCl3/KOH and asks the class of amine. Some students choose secondary because they confuse the test.
Q. An organic compound gives a foul-smelling product when heated with CHCl3 and alcoholic KOH. The compound is:
A. A secondary amine B. A primary amine C. A tertiary amine D. An amide
Trick: A primary amine because only primary amines undergo the carbylamine reaction (RNH2 + CHCl3 + 3KOH gives RNC, an isocyanide with a characteristic foul smell).