NEETAceToday's NEET Daily

Diazonium salts in synthetic organic chemistry: NEET MCQs with answers

57 questions on this topic of Organic Compounds Containing Nitrogen (NEET 2027 syllabus). Here are 12; tap one to see its answer and explanation.

Practise Organic Compounds Containing Nitrogen freeAll Organic Compounds Containing Nitrogen questions

Free with a Google sign-in; NEET Daily needs no sign-in at all.

easy

1. Which of the following functional groups cannot be directly introduced into the benzene ring by nucleophilic substitution of the diazonium group (replacement of -N₂⁺)?

  1. -OH
  2. -I
  3. -F
  4. -CH₃
Show answer and explanation

Answer: (D) -CH₃

The diazonium group (-N₂⁺) can be easily replaced by nucleophiles such as -OH (warm water), -I (KI), -F (HBF₄ followed by heat), -Cl, -Br, and -CN. However, it cannot directly be replaced by an alkyl group like -CH₃.

medium

2. Which of the following compounds CANNOT be prepared directly from benzenediazonium chloride in a single synthetic step?

  1. Benzoic acid
  2. Benzonitrile
  3. Chlorobenzene
  4. Phenol
Show answer and explanation

Answer: (A) Benzoic acid

Chlorobenzene is obtained via Sandmeyer or Gatterman reaction; benzonitrile is formed by reaction with CuCN/KCN; phenol is obtained by warming with water. Benzoic acid cannot be obtained in a single step directly from benzenediazonium chloride; it requires conversion first to benzonitrile followed by acidic or basic hydrolysis.

hard

3. In a laboratory experiment, complete diazotization of 9.3 g of aniline was carried out, followed by treatment with excess potassium iodide (KI). Assuming an 80% practical yield of iodobenzene, what mass of iodobenzene is obtained? (Molar masses: Aniline = 93 g/mol, Iodobenzene = 204 g/mol)

  1. 20.4 g
  2. 10.2 g
  3. 18.36 g
  4. 16.32 g
Show answer and explanation

Answer: (D) 16.32 g

Moles of aniline = 9.3 g / 93 g/mol = 0.10 mol. The theoretical yield of iodobenzene is 0.10 mol, which equals 0.10 mol × 204 g/mol = 20.4 g. At 80% yield, the actual mass obtained = 20.4 g × 0.80 = 16.32 g.

medium

4. Given below are two statements: Statement I: Diazonium salts of aromatic amines are more stable than those of primary aliphatic amines. Statement II: In arenediazonium ions, the positive charge on nitrogen is dispersed over the benzene ring via resonance. In the light of the above statements, choose the most appropriate answer from the options given below:

  1. Both Statement I and Statement II are correct
  2. Statement I is correct but Statement II is incorrect
  3. Statement I is incorrect but Statement II is correct
  4. Both Statement I and Statement II are incorrect
Show answer and explanation

Answer: (A) Both Statement I and Statement II are correct

Arenediazonium salts are stable for a short time in cold solution due to dispersal of the positive charge over the benzene ring through resonance. Aliphatic diazonium salts undergo rapid decomposition even at 0 °C to release N₂.

easy

5. In the azo coupling reaction of benzenediazonium chloride with N,N-dimethylaniline, the product formed is:

  1. Diphenylamine
  2. 2-(Dimethylamino)azobenzene
  3. A mixture of equal amounts of ortho and meta coupled products
  4. 4-(Dimethylamino)azobenzene
Show answer and explanation

Answer: (D) 4-(Dimethylamino)azobenzene

Benzenediazonium chloride undergoes coupling with N,N-dimethylaniline at the para-position relative to the bulky -N(CH₃)₂ group due to steric hindrance at the ortho-positions, yielding 4-(dimethylamino)azobenzene (a butter yellow dye).

hard

6. Match the transformation in List-I with the appropriate reagent in List-II: List-I P. ArN₂⁺Cl⁻ → Ar-H Q. ArN₂⁺Cl⁻ → Ar-OH R. ArN₂⁺Cl⁻ → Ar-NO₂ S. ArN₂⁺Cl⁻ → Ar-I List-II 1. KI 2. H₃PO₂ / H₂O 3. NaNO₂ / Cu, Δ (with fluoroborate) 4. H₂O, warm Choose the correct answer from the options given below:

  1. P-1, Q-4, R-3, S-2
  2. P-4, Q-2, R-3, S-1
  3. P-2, Q-3, R-4, S-1
  4. P-2, Q-4, R-3, S-1
Show answer and explanation

Answer: (D) P-2, Q-4, R-3, S-1

ArN₂⁺ is reduced to Ar-H by H₃PO₂ (P-2). It hydrolyzes to Ar-OH upon warming with water (Q-4). With NaNO₂/Cu and fluoroborate, it gives Ar-NO₂ (R-3). With KI, it produces Ar-I (S-1).

easy

7. Benzenediazonium chloride reacts with an excess of ethanol at room temperature. What are the organic products formed?

  1. Phenol and ethanal
  2. Benzene and ethanal
  3. Phenetole and ethyl chloride
  4. Chlorobenzene and acetic acid
Show answer and explanation

Answer: (B) Benzene and ethanal

Ethanol acts as a mild reducing agent toward arenediazonium salts. Benzenediazonium chloride is reduced to benzene while ethanol is oxidized to ethanal (acetaldehyde), alongside the evolution of N₂ gas and HCl.

medium

8. Which of the following benzenediazonium salts will couple most slowly with phenol in a mildly alkaline buffer?

  1. p-Methoxybenzenediazonium chloride
  2. p-Nitrobenzenediazonium chloride
  3. p-Chlorobenzenediazonium chloride
  4. Benzenediazonium chloride
Show answer and explanation

Answer: (A) p-Methoxybenzenediazonium chloride

Azo coupling is an electrophilic aromatic substitution where the diazonium cation acts as an electrophile. Electron-donating groups like -OCH₃ decrease the electrophilicity of the diazonium group by resonance, thereby making p-methoxybenzenediazonium chloride the least reactive (slowest coupling) among the given options.

easy

9. To prepare 1,3,5-tribromobenzene from aniline, which sequence of reactions should be followed?

  1. (i) NaNO₂ + HCl, 0-5 °C (ii) CuBr / HBr (iii) Br₂ / Fe
  2. (i) Br₂ / H₂O (ii) NaNO₂ + HCl, 0-5 °C (iii) H₃PO₂ / H₂O
  3. (i) H₃PO₂ / H₂O (ii) Br₂ / FeBr₃ (iii) NaNO₂ + HCl
  4. (i) Br₂ / CS₂ (ii) NaNO₂ + HCl, 0-5 °C (iii) CuBr / HBr
Show answer and explanation

Answer: (B) (i) Br₂ / H₂O (ii) NaNO₂ + HCl, 0-5 °C (iii) H₃PO₂ / H₂O

Aniline strongly activates the ring, so bromination with bromine water (Br₂/H₂O) gives 2,4,6-tribromoaniline. Diazotization of 2,4,6-tribromoaniline with NaNO₂ + HCl gives 2,4,6-tribromobenzenediazonium chloride, which upon deamination with H₃PO₂ yields 1,3,5-tribromobenzene.

medium

10. Which of the following substituted arenediazonium chlorides couples most rapidly with phenol in an alkaline medium?

  1. p-Methoxybenzenediazonium chloride
  2. p-Nitrobenzenediazonium chloride
  3. p-Methylbenzenediazonium chloride
  4. p-Chlorobenzenediazonium chloride
Show answer and explanation

Answer: (B) p-Nitrobenzenediazonium chloride

Coupling of a diazonium salt is an electrophilic aromatic substitution reaction where the diazonium cation acts as the electrophile. Strong electron-withdrawing groups such as -NO₂ enhance the positive charge density on the diazonium nitrogen, drastically increasing its electrophilicity and reaction rate.

medium

11. Arenediazonium salts are more stable than aliphatic diazonium salts because:

  1. The positive charge is dispersed over the benzene ring by resonance
  2. They are ionic and aliphatic ones are covalent
  3. They contain no nitrogen
  4. They are formed at high temperature
Show answer and explanation

Answer: (A) The positive charge is dispersed over the benzene ring by resonance

Arenediazonium ions are stabilised by dispersal of positive charge over the benzene ring. They are stable for a short time in solution at low temperature (273-278 K); aliphatic diazonium salts are highly unstable.

NCERT Class 12

easy

12. What is the role of benzenediazonium cation (C₆H₅N₂⁺) in azo coupling reactions with electron-rich aromatic substrates?

  1. Nucleophile
  2. Lewis base
  3. Free radical
  4. Electrophile
Show answer and explanation

Answer: (D) Electrophile

The diazonium ion (ArN₂⁺) has a positive formal charge shared between nitrogen atoms, making the terminal nitrogen electron-deficient. Hence, it acts as a weak electrophile and attacks highly activated aromatic rings (like phenols and arylamines) in an electrophilic aromatic substitution reaction.

Keep going with Organic Compounds Containing Nitrogen. All 223 questions with instant answers, your mistakes saved for revision and your accuracy by topic.
Start practising

Other topics in Organic Compounds Containing Nitrogen