Structure and uses of naphthols MCQs With Answer

Structure and uses of naphthols MCQs With Answer

Naphthols (1‑ and 2‑naphthol) are phenolic derivatives of naphthalene with distinct structural, electronic and pharmacological relevance for B. Pharm students. This concise guide covers structure, isomerism, acidity, resonance stabilization, preparation (sulfonation and alkaline fusion, diazonium hydrolysis), typical reactions (azo coupling, electrophilic substitution, O‑alkylation), analytical tests and major pharmaceutical and industrial uses such as dye intermediates, antioxidants and antiseptics. Keywords: naphthols, 1‑naphthol, 2‑naphthol, structure and uses, MCQs, B. Pharm, pharmaceutical chemistry, azo dyes. ‘Now let’s test your knowledge with 50 MCQs on this topic.’

Q1. Which of the following correctly names 1‑naphthol?

• Alpha‑naphthol
• Beta‑naphthol
• Naphthalenol‑2
• Naphthol‑3

Correct Answer: Alpha‑naphthol

Q2. Which isomer is commonly called beta‑naphthol?

• 1‑naphthol
• 2‑naphthol
• 3‑naphthol
• 4‑naphthol

Correct Answer: 2‑naphthol

Q3. Compared to phenol, naphthols are generally:

• Less acidic due to larger ring system
• About the same acidity as phenol
• More acidic due to greater resonance stabilization of the phenoxide
• Non‑acidic because they are aromatic hydrocarbons

Correct Answer: More acidic due to greater resonance stabilization of the phenoxide

Q4. Between 1‑naphthol and 2‑naphthol, which is slightly more acidic?

• 1‑naphthol
• 2‑naphthol
• They have identical acidity
• Neither is acidic

Correct Answer: 1‑naphthol

Q5. A common industrial route to prepare 2‑naphthol from naphthalene involves:

• Nitration followed by reduction
• Sulfonation followed by alkaline fusion
• Direct hydroxylation using dilute HCl
• Friedel–Crafts acylation

Correct Answer: Sulfonation followed by alkaline fusion

Q6. Naphthols react with diazonium salts in alkaline medium to form:

• Nitro compounds
• Azo dyes via coupling
• Carboxylic acids
• Epoxides

Correct Answer: Azo dyes via coupling

Q7. Which functional group stretch is typically observed for naphthols in IR spectroscopy?

• Sharp carbonyl stretch near 1700 cm‑1
• Broad O–H stretch around 3200–3600 cm‑1
• C≡C stretch near 2100–2200 cm‑1
• No O–H stretch is observed

Correct Answer: Broad O–H stretch around 3200–3600 cm‑1

Q8. Reaction of naphthols with alkyl halides under basic conditions gives:

• Amides
• O‑alkylated ethers (naphthyl ethers)
• Carboxylates
• Hydrazones

Correct Answer: O‑alkylated ethers (naphthyl ethers)

Q9. The phenoxide ion of naphthol is stabilized by:

• Inductive donation only
• Resonance delocalization into the naphthalene system
• Hydrogen bonding exclusively
• Formation of a stable carbocation

Correct Answer: Resonance delocalization into the naphthalene system

Q10. Which test gives a characteristic color with phenolic hydroxyl groups including naphthols?

• Tollen’s test
• FeCl3 test
• Baeyer’s test
• Jone’s oxidation

Correct Answer: FeCl3 test

Q11. Azo coupling with 2‑naphthol typically requires which medium?

• Strong acid
• Neutral water
• Alkaline medium
• Dry ether

Correct Answer: Alkaline medium

Q12. Major pharmaceutical and industrial use of 2‑naphthol is as:

• Antibiotic active ingredient
• Coupling agent in azo dye manufacture
• Direct analgesic for oral use
• Vitamin supplement

Correct Answer: Coupling agent in azo dye manufacture

Q13. Which statement about electrophilic substitution on naphthols is true?

• OH deactivates the ring toward electrophiles
• OH directs new substitution to positions ortho and para relative to itself
• Naphthols cannot undergo electrophilic substitution
• Substitution only occurs at benzylic positions

Correct Answer: OH directs new substitution to positions ortho and para relative to itself

Q14. Formation of sodium naphtholate by treating naphthol with NaOH results in:

• Decreased solubility in water
• Increased solubility in water
• Formation of an insoluble precipitate
• No chemical change

Correct Answer: Increased solubility in water

Q15. Which naphthol is commonly used as an antiseptic and in hair dyes?

• 1‑naphthol
• 3‑naphthol
• 4‑naphthol
• 2‑naphthol is only used industrially

Correct Answer: 1‑naphthol

Q16. In UV spectroscopy, naphthols show strong absorption due to:

• n→π* transitions only
• π→π* transitions in the conjugated aromatic system
• σ→σ* transitions
• No UV activity because they are non‑conjugated

Correct Answer: π→π* transitions in the conjugated aromatic system

Q17. Which reagent can convert a naphthyl sulfonic acid to the corresponding naphthol?

• Alkaline fusion with NaOH
• Catalytic hydrogenation
• Oxidation with KMnO4
• Dehydration using concentrated H2SO4

Correct Answer: Alkaline fusion with NaOH

Q18. The position of maximum electron density in 2‑naphthol favors electrophilic substitution at:

• C1 (alpha position)
• C3 only
• Benzylic methyl groups
• Only on the hydroxyl oxygen

Correct Answer: C1 (alpha position)

Q19. Naphthols can act as antioxidants because they:

• Donate electrons/hydrogen to scavenge free radicals
• Undergo rapid polymerization
• Form chelates with metal ions only
• Inhibit all enzymatic reactions

Correct Answer: Donate electrons/hydrogen to scavenge free radicals

Q20. Which industrial product commonly uses naphthol derivatives as intermediates?

• Azo dyes and pigments
• Sodium chloride manufacture
• Glass fiber production
• Pure oxygen generation

Correct Answer: Azo dyes and pigments

Q21. Which is a correct observation when 1‑naphthol is treated with iron(III) chloride?

• It gives a green precipitate only
• It shows a violet or purple coloration
• There is no color change
• It evolves gas vigorously

Correct Answer: It shows a violet or purple coloration

Q22. O‑alkylation of naphthol under Williamson ether synthesis conditions requires:

• Acidic catalyst and water
• Deprotonation to naphtholate ion followed by alkyl halide
• Direct mixing with alcohol at room temperature
• Oxidative coupling

Correct Answer: Deprotonation to naphtholate ion followed by alkyl halide

Q23. Which of the following is a safety concern with naphthol compounds in pharmaceutical contexts?

• They are completely non‑toxic
• Potential skin sensitization and toxicity on overexposure
• They explode spontaneously in air
• They are inert and pose no hazards

Correct Answer: Potential skin sensitization and toxicity on overexposure

Q24. Hydroxyl substitution at the 2‑position (2‑naphthol) influences reactivity by:

• Removing all resonance stabilization
• Increasing activation of adjacent alpha carbon for substitution
• Making the ring completely unreactive
• Converting it into an aliphatic alcohol

Correct Answer: Increasing activation of adjacent alpha carbon for substitution

Q25. Which analytical technique helps distinguish 1‑ and 2‑naphthol isomers most directly?

• Simple boiling point measurement only
• NMR spectroscopy (proton and carbon shifts)
• Test with silver nitrate
• Litmus paper

Correct Answer: NMR spectroscopy (proton and carbon shifts)

Q26. Nitration of naphthols typically requires control because:

• Nitration is impossible on aromatic rings
• Multiple nitration and oxidation can occur
• It converts naphthols into alkanes
• It produces only a gas

Correct Answer: Multiple nitration and oxidation can occur

Q27. Which derivative of naphthol is widely used as a coupling component in azo dye chemistry?

• 2‑naphthol (beta‑naphthol)
• Hexane‑2‑ol
• Benzoic acid
• Cholesterol

Correct Answer: 2‑naphthol (beta‑naphthol)

Q28. The acidity of naphthols is influenced by:

• Only the solvent used
• Resonance, inductive effects and hydrogen bonding
• The presence of alkyl chains exclusively
• Only temperature

Correct Answer: Resonance, inductive effects and hydrogen bonding

Q29. Which reaction would you use to convert an aryl diazonium salt to a phenol (naphthol analog)?

• Sandmeyer hydrolysis (replacement of diazonium by OH)
• Wurtz reaction
• Hofmann degradation
• Birch reduction

Correct Answer: Sandmeyer hydrolysis (replacement of diazonium by OH)

Q30. In mass spectrometry, fragmentation of naphthols often shows peaks due to:

• Loss of small neutral fragments like H2O or CO
• Only unchanged molecular ion
• Complete lack of fragmentation
• Formation of metal adducts exclusively

Correct Answer: Loss of small neutral fragments like H2O or CO

Q31. Which position in 1‑naphthol is most activated for electrophilic attack?

• Position 2 (adjacent alpha‑position)
• Position 4 only
• Only the hydroxyl oxygen
• Position 8 only

Correct Answer: Position 2 (adjacent alpha‑position)

Q32. Which statement about intramolecular hydrogen bonding in naphthols is correct?

• 2‑Naphthol can exhibit intramolecular hydrogen bonding with neighboring ring pi system affecting properties
• No naphthol can hydrogen bond internally
• Only 3‑naphthol forms a stable five‑membered ring hydrogen bond
• Intramolecular hydrogen bonding converts naphthol into a ketone

Correct Answer: 2‑Naphthol can exhibit intramolecular hydrogen bonding with neighboring ring pi system affecting properties

Q33. Which reagent is commonly used to diazotize an aryl amine precursor before conversion to a naphthol?

• Sodium nitrite and HCl (NaNO2/HCl)
• Sodium borohydride only
• Grignard reagent
• Sulfuric acid and heat only

Correct Answer: Sodium nitrite and HCl (NaNO2/HCl)

Q34. In pharmaceutical formulations, naphthol derivatives are most likely used as:

• Active analgesics in high doses
• Intermediates, preservatives or antiseptic agents
• Primary surfactants
• Inert fillers

Correct Answer: Intermediates, preservatives or antiseptic agents

Q35. The Kolbe–Schmitt reaction is primarily associated with formation of:

• Phenolic carboxylic acids (note: commonly for salicylic acid from phenolate)
• Ether formation from naphthols
• Hydrogenation of naphthalene
• Formation of azo dyes directly

Correct Answer: Phenolic carboxylic acids (note: commonly for salicylic acid from phenolate)

Q36. Which statement best explains why naphthols are good coupling components for azo dye synthesis?

• They are strongly deactivating to electrophiles
• The phenolic OH activates the ring and stabilizes the coupled product by resonance
• They lack conjugation and so do not form colored products
• They react only under extreme conditions, preventing dye formation

Correct Answer: The phenolic OH activates the ring and stabilizes the coupled product by resonance

Q37. Which solvent system is commonly avoided for handling naphthols when planning electrophilic substituents due to potential side reactions?

• Strongly acidic media without control
• Pure water at neutral pH
• Nonpolar solvents like hexane
• Alcohols as mild solvents

Correct Answer: Strongly acidic media without control

Q38. A B. Pharm student analyzing a sample detects a phenolic O–H in IR and an aromatic multiplet in 1H NMR at ~7–8 ppm. The compound is likely a:

• Aliphatic alcohol
• Naphthol or other aromatic phenol
• Simple alkane
• Carboxylic acid only

Correct Answer: Naphthol or other aromatic phenol

Q39. Which of these transformations converts naphthol into a more water‑soluble derivative for dye applications?

• Conversion to its sodium naphtholate salt
• Hydrogenation to decalin derivatives
• Complete oxidation to CO2
• Formation of an ether with bulky alkyl groups

Correct Answer: Conversion to its sodium naphtholate salt

Q40. During electrophilic substitution, stabilization of the sigma complex in naphthols is enhanced by:

• Electron‑donating effect of the OH group
• Electron‑withdrawing halogens only
• Absence of any substituents
• Conversion to sp3 hybridization

Correct Answer: Electron‑donating effect of the OH group

Q41. Which reagent would you use to protect the phenolic OH of a naphthol during a sequence of reactions?

• Acetylation to give O‑acetyl (acetate) derivative
• Strong acid to remove the OH
• Oxidation with chromic acid
• Heating with NaOH to deprotonate only

Correct Answer: Acetylation to give O‑acetyl (acetate) derivative

Q42. The presence of an OH group on the naphthalene ring typically:

• Decreases resonance and makes it less reactive
• Increases electron density and activates the ring toward electrophiles
• Removes all aromaticity
• Converts naphthalene into an aliphatic chain

Correct Answer: Increases electron density and activates the ring toward electrophiles

Q43. Which of the following is a correct safety measure when handling naphthols in the lab?

• No protective equipment is needed
• Use gloves, goggles and work in a fume hood to avoid skin exposure and inhalation
• Store them under direct sunlight at high temperature
• Always mix naphthols with strong oxidizers for stability

Correct Answer: Use gloves, goggles and work in a fume hood to avoid skin exposure and inhalation

Q44. Which product results when naphtholate ion undergoes electrophilic substitution at the carbon adjacent to the oxygen?

• An O‑substituted product only
• A C‑substituted naphthol derivative (carbon‑substituted product)
• Complete loss of aromaticity
• Formation of an aliphatic alcohol

Correct Answer: A C‑substituted naphthol derivative (carbon‑substituted product)

Q45. In dye chemistry, coupling of diazonium salts to 2‑naphthol gives azo dyes that are typically:

• Colorless and unstable
• Highly colored and stable
• Gaseous at room temperature
• Only useful as reducing agents

Correct Answer: Highly colored and stable

Q46. Which is a typical analytical characteristic of a naphtholic phenoxide ion in aqueous solution?

• It is less soluble than the neutral phenol
• It absorbs light at longer wavelengths due to increased conjugation
• It immediately polymerizes
• It forms an insoluble precipitate with Na+

Correct Answer: It absorbs light at longer wavelengths due to increased conjugation

Q47. Which precaution is most important when performing sulfonation of naphthalene to prepare a naphthalenesulfonic acid?

• Avoid strong acids
• Control temperature and acid concentration to limit polynitration or overreaction
• Ensure complete absence of oxygen only
• Run the reaction in open air with direct flame

Correct Answer: Control temperature and acid concentration to limit polynitration or overreaction

Q48. Which property makes naphthols useful as intermediates in organic synthesis?

• The unreactive nature of the aromatic ring
• The activated aromatic ring by OH and easy conversion to salts and ethers
• Their inability to form covalent bonds
• The fact they decompose instantly on contact with bases

Correct Answer: The activated aromatic ring by OH and easy conversion to salts and ethers

Q49. Which derivative of naphthol is commonly used as an antioxidant in rubber and other polymers?

• Naphthylamines only
• Naphthol derivatives such as alkylated naphthols and substituted naphthylamines
• Sodium chloride derivatives
• Unsubstituted benzene

Correct Answer: Naphthol derivatives such as alkylated naphthols and substituted naphthylamines

Q50. For B. Pharm students, understanding naphthols is important because they:

• Have no relevance to pharmaceutical chemistry
• Are central to dye chemistry only and not pharmaceuticals
• Serve as key intermediates, exhibit biological activity and appear in excipient/antiseptic contexts
• Are inert molecules used only in metallurgy

Correct Answer: Serve as key intermediates, exhibit biological activity and appear in excipient/antiseptic contexts

Download