Heterocyclic Chemistry: Quinoline, acridine, purine and indole syntheses MCQs With Answer

Heterocyclic Chemistry: Quinoline, Acridine, Purine and Indole Syntheses MCQs With Answer

Introduction: This quiz collection focuses on the practical and mechanistic aspects of synthesizing four important heterocyclic families — quinolines, acridines, purines and indoles — which are central to medicinal chemistry and M.Pharm curricula. Questions cover classical named methods (Skraup, Friedländer, Fischer, Bernthsen, Traube, Leimgruber–Batcho, Bartoli and others), key reagents, mechanism steps, regiochemistry and typical synthetic applications. The level targets M.Pharm students preparing for MPC 102T Advanced Organic Chemistry I, reinforcing conceptual understanding and reaction choice for designing heterocyclic scaffolds used in drug discovery and nucleoside chemistry.

Q1. In the Skraup synthesis of quinolines which reagent commonly acts as the oxidant?

• Nitrobenzene
• Sulfuric acid
• Glycerol
• Iodine

Correct Answer: Nitrobenzene

Q2. Which aldehyde derivative is the typical partner in the Friedländer quinoline synthesis?

• 2-Aminobenzaldehyde
• Salicylaldehyde
• Benzaldehyde
• Pyridine-2-carboxaldehyde

Correct Answer: 2-Aminobenzaldehyde

Q3. The Doebner–Miller quinoline synthesis most directly uses which type of partner with aniline?

• α,β-Unsaturated carbonyl compounds
• Glycerol
• β-Diketones
• Isatin derivatives

Correct Answer: α,β-Unsaturated carbonyl compounds

Q4. Which classical method converts an aniline and a β-diketone into 2,4-disubstituted quinolines?

• Combes synthesis
• Pfitzinger reaction
• Skraup synthesis
• Bernthsen reaction

Correct Answer: Combes synthesis

Q5. The Pfitzinger reaction is best described as which transformation?

• Isatin plus a carbonyl compound under basic conditions gives quinoline-4-carboxylic acids
• Aniline and glycerol under acid give quinolines
• Diphenylamine and carboxylic acids give acridines
• Phenylhydrazones rearrange to indoles under acid

Correct Answer: Isatin plus a carbonyl compound under basic conditions gives quinoline-4-carboxylic acids

Q6. Which catalyst/promoter is characteristic for the Bernthsen synthesis of acridines?

• Zinc chloride (ZnCl2)
• Palladium on carbon
• Sodium ethoxide
• Aluminum trichloride (AlCl3)

Correct Answer: Zinc chloride (ZnCl2)

Q7. In the Bernthsen acridine synthesis, the immediate carbon source that closes the central ring usually comes from:

• A carboxylic acid (or its derivative)
• Glycerol
• An α,β-unsaturated aldehyde
• An isatin derivative

Correct Answer: A carboxylic acid (or its derivative)

Q8. Which key intermediate is formed initially in the Fischer indole synthesis?

• Phenylhydrazone of a carbonyl compound
• o-Nitrotoluene
• α-Bromoacetophenone
• 2-Aminobenzaldehyde

Correct Answer: Phenylhydrazone of a carbonyl compound

Q9. The Bartoli indole synthesis converts which type of substrate to an indole using excess Grignard reagent?

• Ortho- or vinyl nitroarenes (vinyl nitro compounds)
• Phenylhydrazones
• N-Acyl-o-toluidines
• α-Haloketones

Correct Answer: Ortho- or vinyl nitroarenes (vinyl nitro compounds)

Q10. The Madelung indole synthesis typically requires which strongly basic reagent for cyclization?

• Sodium amide (NaNH2)
• Tertiary butoxide (KOtBu)
• Triethylamine
• Sodium borohydride

Correct Answer: Sodium amide (NaNH2)

Q11. The Leimgruber–Batcho indole synthesis uses which reagent to introduce a dimethylaminomethylene functionality on o‑nitrotoluenes?

• DMF‑dimethyl acetal (DMFDMA)
• Dimethyl sulfate
• Thionyl chloride
• Vilsmeier reagent (POCl3/DMF)

Correct Answer: DMF‑dimethyl acetal (DMFDMA)

Q12. The Bischler–Möhlau route to indoles typically couples anilines with which partner?

• α-Haloketones (α-bromoacetones)
• Vinyl nitro compounds
• 2-Aminobenzaldehyde
• β-Diketones

Correct Answer: α-Haloketones (α-bromoacetones)

Q13. The Traube synthesis of purines commonly begins from which type of heterocyclic precursor?

• 5-Aminopyrimidine-4(1H)-one derivatives
• Imidazole-2-carboxaldehydes
• Purine nucleosides
• 2-Aminobenzaldehydes

Correct Answer: 5-Aminopyrimidine-4(1H)-one derivatives

Q14. Which method is widely used for N‑9 glycosylation of purine bases to form nucleosides in modern synthesis?

• Vorbrüggen glycosylation (silylated base + activated sugar with Lewis acid)
• Fischer esterification
• Bernthsen procedure
• Skraup oxidation

Correct Answer: Vorbrüggen glycosylation (silylated base + activated sugar with Lewis acid)

Q15. In the Friedländer synthesis mechanism the initial condensation usually involves which functional groups?

• Formation of an imine between an amino group and a carbonyl
• Radical coupling of two aromatics
• Nitration followed by reduction
• Direct electrophilic aromatic substitution on benzene

Correct Answer: Formation of an imine between an amino group and a carbonyl

Q16. Acridine derivatives are well known for which biological or physical property relevant to drug research?

• Intercalation into DNA
• Strong nucleophilicity at C2
• High volatility
• Selective phosphorylation of proteins

Correct Answer: Intercalation into DNA

Q17. In the purine nucleoside structure, which ring nitrogen is the common site of glycosidic bond formation to ribose?

• N9
• N1
• N7
• N3

Correct Answer: N9

Q18. The key sigmatropic rearrangement in the Fischer indole synthesis is classified as which type?

• [3,3]-Sigmatropic rearrangement
• [1,2]-Shift
• [2,3]-Sigmatropic rearrangement
• Electrocyclization

Correct Answer: [3,3]-Sigmatropic rearrangement

Q19. What is the principal quinoline product expected from the Friedländer condensation of 2‑aminobenzaldehyde with acetone?

• 2-Methylquinoline
• 4-Methylquinoline
• 2,4-Dimethylquinoline
• Quinoline-4-carboxylic acid

Correct Answer: 2-Methylquinoline

Q20. Which simple aromatic amine is the standard starting point for classical Bernthsen-type acridine syntheses?

• Diphenylamine
• Aniline
• Pyridine
• o-Toluidine

Correct Answer: Diphenylamine

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