Reactions of furan MCQs With Answer

Reactions of furan MCQs With Answer

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Reactions of furan MCQs With Answer

Understanding the reactions of furan is essential for B.Pharm students studying heterocyclic chemistry and drug design. This concise guide focuses on key furan reactions—electrophilic substitution, Diels–Alder behavior, oxidation to maleic derivatives, hydrogenation to tetrahydrofuran, lithiation, and common synthetic routes like Paal–Knorr—while highlighting mechanistic reasons, regioselectivity (2‑position), and pharmaceutical relevance such as metabolic bioactivation and hepatotoxicity. The keyword-rich overview helps reinforce reaction conditions, reagents (NBS, KMnO4, Vilsmeier reagent, Pd catalysts), and protection strategies. Ideal for exam prep and practical understanding. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which of the following correctly states the number of pi electrons that contribute to furan’s aromaticity?

  • 4 pi electrons
  • 6 pi electrons
  • 8 pi electrons
  • 10 pi electrons

Correct Answer: 6 pi electrons

Q2. In electrophilic aromatic substitution (EAS) of furan, which position is most reactive?

  • 2-position (alpha)
  • 3-position (beta)
  • Oxygen atom
  • 4-position

Correct Answer: 2-position (alpha)

Q3. Why is furan more reactive toward electrophiles than benzene?

  • Ring strain makes it highly reactive
  • Oxygen lone pair increases electron density at the ring, especially at C2
  • Furan has more pi bonds than benzene
  • It has a positive charge in the ground state

Correct Answer: Oxygen lone pair increases electron density at the ring, especially at C2

Q4. What is a common outcome when attempting Friedel–Crafts acylation on unsubstituted furan under strong Lewis acid conditions?

  • Clean 3-acylation only
  • Clean 2-acylation without issues
  • Extensive polymerization and decomposition
  • No reaction at all

Correct Answer: Extensive polymerization and decomposition

Q5. In Diels–Alder chemistry, furan most commonly behaves as which component?

  • Diene
  • Dienophile
  • Neither diene nor dienophile
  • Only a radical initiator

Correct Answer: Diene

Q6. Oxidative cleavage of the furan ring typically yields which major product?

  • Maleic anhydride (or maleic acid)
  • Succinic acid
  • Acetic acid
  • Tartaric acid

Correct Answer: Maleic anhydride (or maleic acid)

Q7. Catalytic hydrogenation of furan (complete hydrogenation of the ring) gives:

  • Tetrahydrofuran (THF)
  • Pyrrole
  • Benzene
  • Furfuryl alcohol

Correct Answer: Tetrahydrofuran (THF)

Q8. Directed lithiation of furan typically occurs at which position?

  • 2-position (alpha)
  • 3-position (beta)
  • On oxygen
  • 4-position

Correct Answer: 2-position (alpha)

Q9. Does furan readily undergo nucleophilic aromatic substitution (SNAr) under normal conditions?

  • Yes, very readily
  • Only under radical conditions
  • No, SNAr is rare for furan
  • Only in presence of strong base and heat

Correct Answer: No, SNAr is rare for furan

Q10. Under strong protonating conditions, where is the initial protonation of furan most likely to occur?

  • On the oxygen atom forming an oxonium ion
  • At C2
  • At C3
  • Simultaneous at C2 and C3

Correct Answer: On the oxygen atom forming an oxonium ion

Q11. Order the following heterocycles by decreasing reactivity toward electrophilic substitution: pyrrole, furan, thiophene.

  • Pyrrole > furan > thiophene
  • Furan > pyrrole > thiophene
  • Thiophene > furan > pyrrole
  • Pyrrole > thiophene > furan

Correct Answer: Pyrrole > furan > thiophene

Q12. The highest electron density in furan is located at which atoms?

  • 2 and 5 positions (alpha carbons)
  • 3 and 4 positions (beta carbons)
  • Only on the oxygen atom
  • Uniform across all ring carbons

Correct Answer: 2 and 5 positions (alpha carbons)

Q13. Which reagent is commonly used for selective bromination at the 2-position of furan?

  • N-bromosuccinimide (NBS)
  • Br2/FeBr3
  • HBr
  • NaBr

Correct Answer: N-bromosuccinimide (NBS)

Q14. Complete oxidative degradation of furan under strong oxidants typically leads to formation of:

  • Maleic acid / maleic anhydride
  • Glutaric acid
  • Benzoic acid
  • Citric acid

Correct Answer: Maleic acid / maleic anhydride

Q15. Compared to benzene, furan’s aromatic stabilization is:

  • Greater than benzene
  • About the same as benzene
  • Less than benzene
  • Non-aromatic

Correct Answer: Less than benzene

Q16. Typical 1H NMR chemical shift range for furan ring protons lies approximately in:

  • 6.0–7.5 ppm
  • 2.0–3.5 ppm
  • 8.0–9.5 ppm
  • 0.5–2.0 ppm

Correct Answer: 6.0–7.5 ppm

Q17. Which condition is commonly used for catalytic hydrogenation of furan to tetrahydrofuran?

  • H2 with Pd/C or Pt catalyst
  • O2 with Cu catalyst
  • HCl alone
  • Br2 in CCl4

Correct Answer: H2 with Pd/C or Pt catalyst

Q18. A practical protection strategy for the furan ring during multi-step synthesis is:

  • Formation of a Diels–Alder adduct with maleic anhydride
  • Oxidation to maleic anhydride immediately
  • Alkylation at oxygen
  • Chlorination at the 3-position

Correct Answer: Formation of a Diels–Alder adduct with maleic anhydride

Q19. Furan-containing drugs can pose what major metabolic risk?

  • Bioactivation to reactive metabolites causing hepatotoxicity
  • Complete inertness to metabolism
  • Selective kidney accumulation only
  • Universal safety with no toxicity

Correct Answer: Bioactivation to reactive metabolites causing hepatotoxicity

Q20. The Vilsmeier–Haack reaction on furan typically introduces which functional group at C2?

  • Formyl group (gives 2‑formylfuran)
  • Nitro group
  • Methyl group
  • Hydroxyl group

Correct Answer: Formyl group (gives 2‑formylfuran)

Q21. Reaction of furan with singlet oxygen (1O2) commonly yields:

  • Endoperoxides or hydroperoxide intermediates leading to ring cleavage
  • Direct hydrogenation to THF
  • Simple chlorinated products
  • No reaction at all

Correct Answer: Endoperoxides or hydroperoxide intermediates leading to ring cleavage

Q22. Relative to tetrahydrofuran (THF), furan is:

  • More basic
  • Equally basic
  • Less basic because the oxygen lone pair is delocalized
  • Amphoteric

Correct Answer: Less basic because the oxygen lone pair is delocalized

Q23. Friedel–Crafts acylation of furan is best described as:

  • Readily performed under harsh Lewis acid conditions with high yields
  • Possible under very mild conditions but often problematic due to polymerization
  • Impossible under any conditions
  • Always gives 3-acylation exclusively

Correct Answer: Possible under very mild conditions but often problematic due to polymerization

Q24. Which oxidant is commonly used in the laboratory to convert furan to maleic acid derivatives?

  • KMnO4 (potassium permanganate)
  • PCC
  • LiAlH4
  • NaBH4

Correct Answer: KMnO4 (potassium permanganate)

Q25. Which of the following marketed drugs contains a furan or nitrofuran moiety?

  • Nitrofurantoin
  • Aspirin
  • Ibuprofen
  • Metformin

Correct Answer: Nitrofurantoin

Q26. Which rule explains the aromatic electron count for furan?

  • Hückel’s rule (4n + 2 pi electrons)
  • Bredt’s rule
  • Zaitsev’s rule
  • Markovnikov’s rule

Correct Answer: Hückel’s rule (4n + 2 pi electrons)

Q27. Which resonance form is an important contributor to furan’s electronic structure?

  • Form with oxygen bearing a positive charge and an aromatic sextet
  • Form with oxygen bearing a negative charge and no aromaticity
  • Non-aromatic diradical form
  • Structure with an exocyclic double bond only

Correct Answer: Form with oxygen bearing a positive charge and an aromatic sextet

Q28. The Diels–Alder adduct of furan with maleic anhydride typically favors which stereochemistry?

  • Exo exclusively
  • Endo preference
  • No stereoselectivity
  • Trans addition only

Correct Answer: Endo preference

Q29. Which catalytic strategy is commonly used for direct C–H arylation of furan at the 2-position?

  • Palladium-catalyzed direct arylation (C–H activation)
  • Nitration followed by reduction
  • Free-radical bromination only
  • Electrophilic chlorination at oxygen

Correct Answer: Palladium-catalyzed direct arylation (C–H activation)

Q30. For selective 2-chlorination of furan, which reagent is most appropriate?

  • N-chlorosuccinimide (NCS)
  • NaCl in water
  • SOCl2
  • HCl gas

Correct Answer: N-chlorosuccinimide (NCS)

Q31. Which classical method synthesizes substituted furans from 1,4-diketones?

  • Paal–Knorr synthesis
  • Birch reduction
  • Grignard addition only
  • Wurtz coupling

Correct Answer: Paal–Knorr synthesis

Q32. Compared to pyrrole, furan’s susceptibility to electrophilic attack is:

  • Greater than pyrrole
  • Less than pyrrole
  • Equal to pyrrole
  • Zero (furan is inert)

Correct Answer: Less than pyrrole

Q33. Exposure of furan to strong acids commonly leads to which process?

  • Polymerization and decomposition
  • Stable salt formation without further reaction
  • Immediate hydrogenation
  • No reaction

Correct Answer: Polymerization and decomposition

Q34. Photochemical reaction of furan in oxygenated solvents can lead to:

  • Formation of peroxides and photooxidation products
  • Complete inertness to light
  • Selective hydrogenation to THF
  • Formation of nitro compounds

Correct Answer: Formation of peroxides and photooxidation products

Q35. Oxidation of alkyl-substituted furans (e.g., 2,5-dimethylfuran) with strong oxidants typically yields:

  • Oxidized dicarboxylic acids such as dimethylmaleic derivatives or ultimately maleic acid derivatives
  • Only alcohols
  • Aromatic benzene derivatives
  • Unchanged starting material

Correct Answer: Oxidized dicarboxylic acids such as dimethylmaleic derivatives or ultimately maleic acid derivatives

Q36. Introduction of electron-withdrawing substituents on the furan ring generally has what effect?

  • Increases reactivity toward electrophiles
  • Decreases reactivity toward electrophiles and stabilizes against polymerization
  • Eliminates aromaticity completely
  • Makes furan a better nucleophile

Correct Answer: Decreases reactivity toward electrophiles and stabilizes against polymerization

Q37. Which reagent/condition is commonly used to generate 2-lithiofuran selectively?

  • n-BuLi at low temperature (e.g., −78 °C)
  • HBr at room temperature
  • KMnO4 oxidation
  • Pd/C and H2

Correct Answer: n-BuLi at low temperature (e.g., −78 °C)

Q38. After halogenation at C2, which cross-coupling method is routinely used to introduce aryl groups onto furan?

  • Suzuki coupling using boronic acids and Pd catalyst
  • Grignard formation followed by carbonation
  • Paal–Knorr condensation
  • Ozonolysis

Correct Answer: Suzuki coupling using boronic acids and Pd catalyst

Q39. The highest-occupied molecular orbital (HOMO) in furan primarily has large coefficients at which positions?

  • C2 and C5 (alpha carbons)
  • C3 and C4 (beta carbons)
  • Only on oxygen
  • Evenly distributed over all atoms

Correct Answer: C2 and C5 (alpha carbons)

Q40. Which solvent is commonly used for organolithium-mediated metalation of furan derivatives?

  • Tetrahydrofuran (THF)
  • Water
  • Carbon tetrachloride
  • Methanol

Correct Answer: Tetrahydrofuran (THF)

Q41. Nitration of furan under standard conditions typically results in:

  • Clean nitration at C3
  • Strong oxidation, polymerization, or decomposition rather than clean nitration
  • Formation of nitrosyl-furan complexes only
  • No reaction due to strong deactivation

Correct Answer: Strong oxidation, polymerization, or decomposition rather than clean nitration

Q42. In drug metabolism, cytochrome P450-mediated bioactivation of furan often starts with which transformation?

  • Epoxidation of the 2,3-double bond followed by ring opening to reactive species
  • Direct reduction to THF
  • Immediate conjugation to glucuronide without activation
  • C–H insertion at a saturated carbon

Correct Answer: Epoxidation of the 2,3-double bond followed by ring opening to reactive species

Q43. Furan can be used as a synthetic equivalent (masked form) of which functional motif after appropriate transformations?

  • 1,4‑Dicarbonyl compounds (masked by Diels–Alder strategies)
  • Simple alkanes only
  • Primary amines
  • Alcohols exclusively

Correct Answer: 1,4‑Dicarbonyl compounds (masked by Diels–Alder strategies)

Q44. For selective formylation of furan at C2, which reagent combination is preferred?

  • Vilsmeier–Haack reagent (DMF/POCl3)
  • KMnO4 alone
  • H2/Pd
  • Br2/FeBr3

Correct Answer: Vilsmeier–Haack reagent (DMF/POCl3)

Q45. Is furan considered aromatic according to Hückel’s rule?

  • Yes, it is aromatic
  • No, it is antiaromatic
  • No, it is non-aromatic
  • Only under acidic conditions

Correct Answer: Yes, it is aromatic

Q46. Which condition commonly leads to nucleophile-induced ring opening of activated furans?

  • Acid-catalyzed hydration followed by nucleophilic attack
  • Strong base without any electrophile
  • Neutral solvent at 0 °C only
  • Pure photochemical conditions without oxygen

Correct Answer: Acid-catalyzed hydration followed by nucleophilic attack

Q47. Which oxidant is commonly used in practice to convert furan to maleic anhydride or maleic acid derivatives?

  • Potassium permanganate (KMnO4)
  • PCC (pyridinium chlorochromate)
  • LiAlH4
  • Toluenesulfonic acid

Correct Answer: Potassium permanganate (KMnO4)

Q48. Which spectroscopic technique provides clear evidence for substitution at the 2-position of furan?

  • 1H NMR showing characteristic downfield shift of the remaining alpha proton
  • Simple UV–Vis only
  • Mass spectrometry alone without MS/MS
  • Flame photometry

Correct Answer: 1H NMR showing characteristic downfield shift of the remaining alpha proton

Q49. The presence of a furan ring in a drug candidate most often contributes which concern in medicinal chemistry?

  • Metabolic liability due to potential bioactivation
  • Guaranteed high oral bioavailability
  • No metabolic processing at all
  • Complete lack of biological activity

Correct Answer: Metabolic liability due to potential bioactivation

Q50. The regioselectivity of electrophilic substitution at the 2-position of furan is best explained by:

  • Better resonance stabilization of the sigma complex when substitution is at C2
  • Steric hindrance that prevents substitution at C2
  • Random distribution of electrophiles
  • The oxygen atom preventing substitution at C2

Correct Answer: Better resonance stabilization of the sigma complex when substitution is at C2

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