Structure and uses of phenol MCQs With Answer

Structure and uses of phenol MCQs With Answer are vital for B.Pharm students diving into medicinal chemistry, pharmaceutical analysis, and formulation science. This concise introduction emphasizes phenol’s aromatic ring bearing a hydroxyl group, resonance stabilization, acidity (pKa ~10), electrophilic substitution patterns, key reactions (Kolbe–Schmitt, Reimer–Tiemann, Williamson synthesis), important derivatives, industrial applications (resins, antiseptics, bisphenol A), analytical tests (FeCl3), and safety/handling. The questions focus on mechanism-based understanding, synthesis routes, and therapeutic relevance to drug design. Answers are provided for self-assessment and timed practice. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which structural feature defines phenol?

• A hydroxyl group bonded to an aliphatic carbon
• An ether linkage attached to benzene
• A hydroxyl group directly bonded to a benzene ring
• A carbonyl group attached to an aromatic ring

Correct Answer: A hydroxyl group directly bonded to a benzene ring

Q2. Which statement best explains phenol’s acidity compared to ethanol?

• Phenol is less acidic because the OH is on an sp2 carbon
• Phenol is more acidic due to resonance stabilization of the phenoxide ion
• Phenol and ethanol have similar acidity because both have OH groups
• Phenol is less acidic because aromatic rings withdraw electron density

Correct Answer: Phenol is more acidic due to resonance stabilization of the phenoxide ion

Q3. What is the approximate pKa of phenol?

• ~16
• ~7
• ~10
• ~4

Correct Answer: ~10

Q4. Which reagent gives a characteristic violet color with phenol in qualitative tests?

• Bromine water
• Ferric chloride solution
• 2,4-Dinitrophenylhydrazine
• Tollen’s reagent

Correct Answer: Ferric chloride solution

Q5. The -OH group on phenol is generally classified as what kind of directing group in electrophilic aromatic substitution?

• Meta-directing deactivator
• Ortho/para directing activator
• Non-directing neutral group
• Para-only directing deactivator

Correct Answer: Ortho/para directing activator

Q6. Which product predominates when phenol is nitrated under mild conditions?

• Nitrobenzene (only)
• Predominantly ortho- and para-nitrophenols
• Only meta-nitrophenol
• No reaction occurs

Correct Answer: Predominantly ortho- and para-nitrophenols

Q7. What is the outcome when phenol is treated with bromine water at room temperature?

• No reaction
• Formation of 2,4,6-tribromophenol as a precipitate
• Formation of bromobenzene via substitution at carbon
• Oxidation to benzoquinone

Correct Answer: Formation of 2,4,6-tribromophenol as a precipitate

Q8. Which method is commonly used to synthesize phenolic ethers from phenol?

• Friedel–Crafts acylation
• Kolbe–Schmitt carboxylation
• Williamson ether synthesis (phenoxide + alkyl halide)
• Birch reduction

Correct Answer: Williamson ether synthesis (phenoxide + alkyl halide)

Q9. Which reagent converts phenol into its phenoxide salt?

• Sodium bicarbonate
• Sodium hydroxide
• Silver nitrate
• Acetic acid

Correct Answer: Sodium hydroxide

Q10. Why does phenol react with NaOH but not with NaHCO3 to form a salt?

• Phenol is a stronger acid than carbonic acid
• Phenol is a weaker acid than carbonic acid so NaHCO3 cannot deprotonate it
• NaHCO3 reacts violently with phenol
• Phenol is insoluble in water so no reaction occurs

Correct Answer: Phenol is a weaker acid than carbonic acid so NaHCO3 cannot deprotonate it

Q11. The Kolbe–Schmitt reaction on phenoxide ion primarily yields which compound?

• 4-Nitrophenol
• Phenyl acetate
• Salicylic acid (ortho-hydroxybenzoic acid)
• Benzoic acid

Correct Answer: Salicylic acid (ortho-hydroxybenzoic acid)

Q12. Reimer–Tiemann reaction on phenol is used to introduce which functional group?

• Nitro group at para position
• Formyl group at ortho position (salicylaldehyde)
• Carboxyl group at para position
• Alkyl group on oxygen

Correct Answer: Formyl group at ortho position (salicylaldehyde)

Q13. Why is phenol more reactive towards electrophilic substitution than benzene?

• The OH group withdraws electron density from the ring
• The OH group donates electron density by resonance, increasing ring activation
• Phenol has less resonance stabilization than benzene
• Phenol has a positive charge on the ring carbon

Correct Answer: The OH group donates electron density by resonance, increasing ring activation

Q14. Which compound is an industrial product synthesized from phenol and acetone?

• Bisphenol A
• Phenylalanine
• Paracetamol
• Phenolphthalein

Correct Answer: Bisphenol A

Q15. Which derivative of phenol is commonly used as an antiseptic/disinfectant?

• Phenylalanine
• Cresols (methylphenols)
• Benzoic acid
• Toluene

Correct Answer: Cresols (methylphenols)

Q16. Which oxidizing agent can convert phenol to p-benzoquinone?

• Sodium borohydride (NaBH4)
• Chromic acid (H2CrO4) or dichromate under controlled conditions
• Tertiary butylhydroperoxide producing radical polymerization
• Hydrogen gas with Pd/C

Correct Answer: Chromic acid (H2CrO4) or dichromate under controlled conditions

Q17. Why do phenolic O–H bonds show lower stretching frequencies in IR compared to aliphatic alcohols?

• Stronger hydrogen bonding and resonance reduce O–H bond strength
• Phenol has no hydrogen bonding
• Ring vibrations mask O–H stretch completely
• O–H stretch is absent in phenols

Correct Answer: Stronger hydrogen bonding and resonance reduce O–H bond strength

Q18. In electrophilic aromatic substitution, which position on phenol is least favored?

• Ortho
• Para
• Meta
• All are equally favored

Correct Answer: Meta

Q19. Which protective group strategy is commonly used to prevent phenol from reacting during synthesis?

• Conversion to phenoxide salt
• Formation of an ether (e.g., methyl or benzyl ether)
• Direct acetylation to yield a carboxylic acid
• Oxidation to quinone temporarily

Correct Answer: Formation of an ether (e.g., methyl or benzyl ether)

Q20. Phenol reacts with acetic anhydride to yield which product?

• Phenyl acetate (acetylation of OH to give acetate ester)
• Aniline
• Benzoic acid
• Phenol diacetate only under radical conditions

Correct Answer: Phenyl acetate (acetylation of OH to give acetate ester)

Q21. Which statement correctly contrasts O-alkylation vs C-alkylation of phenol?

• O-alkylation gives ethers; C-alkylation gives alkylation on the aromatic ring
• They are the same reaction with different names
• C-alkylation always occurs with SN2 reagents
• O-alkylation yields phenyl ketones

Correct Answer: O-alkylation gives ethers; C-alkylation gives alkylation on the aromatic ring

Q22. Which reagent is suitable to prepare phenoxide ion quantitatively for Williamson synthesis?

• Pyridinium chlorochromate (PCC)
• Sodium hydride (NaH) or NaOH
• Hydrogen bromide
• AlCl3

Correct Answer: Sodium hydride (NaH) or NaOH

Q23. Why do phenols undergo electrophilic substitution more readily than benzene even in dilute acids?

• Because the OH group forms a complex that deactivates the ring
• Because resonance donation from oxygen increases electron density at ring positions
• Because phenol cannot form carbocations
• Because phenol is insoluble and concentrates reagents

Correct Answer: Because resonance donation from oxygen increases electron density at ring positions

Q24. Which phenolic derivative is an important intermediate in aspirin (acetylsalicylic acid) synthesis?

• p-Nitrophenol
• Salicylic acid (o-hydroxybenzoic acid)
• Phenylalanine
• Phenyl acetate

Correct Answer: Salicylic acid (o-hydroxybenzoic acid)

Q25. Friedel–Crafts alkylation on phenol is often problematic because:

• Phenol is too deactivated to undergo the reaction
• The -OH strongly activates the ring and forms complexes with Lewis acids, causing polymerization/tar
• The reaction yields only meta products
• Phenol does not dissolve in common solvents

Correct Answer: The -OH strongly activates the ring and forms complexes with Lewis acids, causing polymerization/tar

Q26. Which functional group transformation converts phenol to a better leaving group for nucleophilic aromatic substitution?

• Acetylation of OH to acetate
• Conversion to a sulfonate ester (e.g., tosylate)
• Oxidation to quinone
• Methylation to an ether

Correct Answer: Conversion to a sulfonate ester (e.g., tosylate)

Q27. Which of the following phenols would give the strongest color with FeCl3?

• Phenol with no other substituents
• 4-Nitrophenol
• Phenol with electron-donating groups that increase complexation (e.g., dihydroxy phenols)
• Tert-butylphenol

Correct Answer: Phenol with electron-donating groups that increase complexation (e.g., dihydroxy phenols)

Q28. What is the product when phenol undergoes Kolbe electrochemical carboxylation (Kolbe process) under CO2 and base?

• Para-nitrophenol
• Ortho- or para-hydroxybenzoate salts, predominantly ortho (salicylate)
• Phenyl acetate
• Benzoquinone

Correct Answer: Ortho- or para-hydroxybenzoate salts, predominantly ortho (salicylate)

Q29. Which safety concern is most associated with handling concentrated phenol in pharmaceutical labs?

• It is non-toxic and requires no PPE
• Phenol is corrosive and can cause severe burns and systemic toxicity on skin contact
• Phenol is an oxidizer that explodes on contact with organic solvents
• Phenol is completely inert and non-flammable

Correct Answer: Phenol is corrosive and can cause severe burns and systemic toxicity on skin contact

Q30. Which pathway is commonly used industrially to produce phenol from benzene?

• Nitration followed by reduction and hydrolysis
• Cumene process (oxidation of cumene to cumene hydroperoxide, then cleavage to phenol and acetone)
• Direct hydration of benzene
• Kolbe–Schmitt reaction on benzaldehyde

Correct Answer: Cumene process (oxidation of cumene to cumene hydroperoxide, then cleavage to phenol and acetone)

Q31. Which of the following is a common analytical method to quantify phenol in pharmaceutical formulations?

• Infrared spectroscopy only
• UV-Vis spectrophotometry after derivatization
• Titration with HCl without indicators
• NMR without solvent

Correct Answer: UV-Vis spectrophotometry after derivatization

Q32. Which reaction sequence converts phenol to salicylic acid industrially or in labs?

• Williamson ether synthesis followed by hydrolysis
• Kolbe–Schmitt reaction (CO2 insertion into phenoxide, then acidification)
• Direct hydrogenation of phenol
• Reimer–Tiemann to give salicylaldehyde then oxidation

Correct Answer: Kolbe–Schmitt reaction (CO2 insertion into phenoxide, then acidification)

Q33. Which substituent on phenol will decrease its acidity relative to phenol?

• Nitro group at para position
• Fluoro group at ortho position
• Methyl group at para position (electron-donating)
• Carboxyl group at meta position

Correct Answer: Methyl group at para position (electron-donating)

Q34. Phenol forms hydrogen bonds. How does this affect its boiling point relative to benzene?

• Phenol has a lower boiling point than benzene
• Phenol has a significantly higher boiling point due to hydrogen bonding
• Both have identical boiling points
• Boiling point decreases in phenol due to resonance

Correct Answer: Phenol has a significantly higher boiling point due to hydrogen bonding

Q35. In a Williamson synthesis starting from phenol, which intermediate is essential?

• Phenyl cation
• Phenoxide ion
• Phenyl radical
• Phenyl halide

Correct Answer: Phenoxide ion

Q36. Which reaction will convert phenol into anisole (methoxybenzene)?

• Methylation of phenol using methyl iodide and base (Williamson ether synthesis)
• Nitration followed by reduction
• Hydrogenation over Pd/C
• Kolbe–Schmitt reaction

Correct Answer: Methylation of phenol using methyl iodide and base (Williamson ether synthesis)

Q37. Which statement about ortho/para ratio in electrophilic substitution of phenol is true?

• Para product is always formed exclusively
• Ortho products usually predominate due to both electronic activation and steric factors sometimes favoring para
• Meta products dominate because OH is meta-directing
• Only substitution at carbon-1 occurs

Correct Answer: Ortho products usually predominate due to both electronic activation and steric factors sometimes favoring para

Q38. Which reagent would selectively protect phenol as a benzyl ether (useful for later deprotection)?

• Benzyl bromide with base (e.g., NaH)
• Acetic anhydride alone
• Br2 in water
• HNO3/H2SO4

Correct Answer: Benzyl bromide with base (e.g., NaH)

Q39. Which of the following is a major industrial use of phenol?

• Synthesis of phenol-formaldehyde resins (Bakelite)
• As a final active pharmaceutical ingredient without modification
• Primary fuel in combustion engines
• Food additive as sweetener

Correct Answer: Synthesis of phenol-formaldehyde resins (Bakelite)

Q40. What product results from oxidation of para-cresol (4-methylphenol) under strong oxidation?

• p-Hydroxybenzoic acid
• Toluene
• p-Cresol dimer only
• Phenylalanine

Correct Answer: p-Hydroxybenzoic acid

Q41. Which reagent would convert phenol into a good leaving group for nucleophilic aromatic substitution at oxygen?

• Tosyl chloride (to form tosylate)
• Hydrochloric acid only
• Silver oxide
• Sodium hydroxide only

Correct Answer: Tosyl chloride (to form tosylate)

Q42. Which spectral change indicates hydrogen bonding in phenol’s 1H NMR compared to aliphatic alcohol?

• Phenolic OH appears at very high-field (~0.5 ppm)
• Phenolic OH is broad and can appear downfield (around 4–7+ ppm depending on H-bonding)
• Phenolic OH always disappears in all solvents
• Phenolic OH gives a sharp multiplet only

Correct Answer: Phenolic OH is broad and can appear downfield (around 4–7+ ppm depending on H-bonding)

Q43. Which of the following is NOT a typical reaction of phenol?

• Nitration
• Kolbe–Schmitt carboxylation
• Direct nucleophilic aliphatic substitution on phenol oxygen without activation
• Bromination at ortho/para positions

Correct Answer: Direct nucleophilic aliphatic substitution on phenol oxygen without activation

Q44. Which heteroatom-containing reagent is often used to convert phenols into aryl halides via diazonium chemistry (indirect route)?

• Formation of aryl diazonium from aniline derivative followed by Sandmeyer reaction
• Direct chlorination with HCl only
• Ozonolysis
• Hydrogenation with Raney nickel

Correct Answer: Formation of aryl diazonium from aniline derivative followed by Sandmeyer reaction

Q45. Which statement about electronic effects on phenol acidity is correct?

• Electron-withdrawing groups increase acidity by stabilizing the phenoxide ion
• Electron-donating groups increase acidity by destabilizing the phenoxide ion
• Substituents have no effect on phenol acidity
• Only steric effects matter, not electronic

Correct Answer: Electron-withdrawing groups increase acidity by stabilizing the phenoxide ion

Q46. Which reaction converts phenol to a nitrophenol preferentially at para position under controlled conditions?

• Strong nitration (conc. HNO3/H2SO4) at low temperature to favor para alongside ortho
• Hydrogenation
• Kolbe–Schmitt
• Williamson synthesis

Correct Answer: Strong nitration (conc. HNO3/H2SO4) at low temperature to favor para alongside ortho

Q47. Phenol derivatives are used in drug design mainly because:

• Phenolic OH groups confer strong basicity
• Phenolic OH can participate in hydrogen bonding and modulate polarity and reactivity
• Phenols are always metabolically stable
• Phenols cannot be modified chemically

Correct Answer: Phenolic OH can participate in hydrogen bonding and modulate polarity and reactivity

Q48. What is a likely metabolic transformation of phenolic drugs in the body?

• Methylation (O-methylation) and conjugation (glucuronidation, sulfation)
• Formation of stable polymers
• Complete resistance to metabolism
• Conversion to alkanes

Correct Answer: Methylation (O-methylation) and conjugation (glucuronidation, sulfation)

Q49. In designing a synthetic route, why might a chemist convert phenol to its acetate (phenyl acetate) temporarily?

• To permanently deactivate the molecule
• To protect the OH from electrophilic aromatic substitution and prevent overreaction
• To increase acidity for Kolbe–Schmitt immediately
• To oxidize it into quinone

Correct Answer: To protect the OH from electrophilic aromatic substitution and prevent overreaction

Q50. Which of the following best describes why phenol shows increased reactivity toward electrophiles at ortho/para positions?

• Inductive withdrawal by oxygen increases electron density at meta positions
• Resonance donation by the lone pair on oxygen increases electron density at ortho and para carbons
• Steric hindrance prevents reaction at ortho/para
• Phenol is actually less reactive at ortho/para

Correct Answer: Resonance donation by the lone pair on oxygen increases electron density at ortho and para carbons

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com