Terpenoids – Menthol MCQs With Answer

Terpenoids – Menthol MCQs With Answer

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Terpenoids – Menthol MCQs With Answer

Menthol is a widely studied monoterpenoid with significant pharmaceutical relevance for B. Pharm students. This introduction covers menthol’s chemistry, stereochemistry, biosynthesis from geranyl diphosphate, physical properties, analytical methods (GC, GC‑MS, NMR, IR), formulation roles (topical analgesics, cough lozenges, penetration enhancer), pharmacology (TRPM8‑mediated cooling, mild local anesthetic action), and quality control considerations. Understanding menthol’s natural occurrence in peppermint oil, industrial isolation, synthetic routes, and safety/toxicity profiles is essential for pharmaceutical formulation and analysis. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What chemical class does menthol belong to?

  • Monoterpenoid alcohol
  • Sesquiterpene ketone
  • Phenolic antioxidant
  • Polyketide ester

Correct Answer: Monoterpenoid alcohol

Q2. What is the primary natural source of commercial menthol?

  • Peppermint oil (Mentha × piperita)
  • Cinnamon bark oil
  • Eucalyptus oil
  • Synthetic petroleum feedstock

Correct Answer: Peppermint oil (Mentha × piperita)

Q3. How many stereoisomers are possible for menthol due to its stereocenters?

  • Two stereoisomers
  • Four stereoisomers
  • Eight stereoisomers
  • Sixteen stereoisomers

Correct Answer: Eight stereoisomers

Q4. Which molecular target mediates menthol’s characteristic cooling sensation?

  • TRPM8 cold‑sensitive ion channel
  • Histamine H1 receptor
  • Beta‑2 adrenergic receptor
  • Acetylcholinesterase enzyme

Correct Answer: TRPM8 cold‑sensitive ion channel

Q5. Which menthol enantiomer is predominantly found in nature and associated with stronger cooling?

  • (+)-Menthol (d‑menthol)
  • (-)-Menthol (levomenthol)
  • Racemate of menthol
  • Menthone isomer

Correct Answer: (-)-Menthol (levomenthol)

Q6. Which statement best describes menthol’s solubility?

  • Sparingly soluble in water, soluble in ethanol and oils
  • Highly soluble in water and insoluble in organic solvents
  • Only soluble in polar aprotic solvents
  • Insoluble in both water and ethanol

Correct Answer: Sparingly soluble in water, soluble in ethanol and oils

Q7. What is the approximate melting point range of natural menthol?

  • −10 to −5 °C
  • 0 to 5 °C
  • 34 to 36 °C
  • 80 to 85 °C

Correct Answer: 34 to 36 °C

Q8. Which analytical technique is most commonly used to quantify menthol in essential oils and formulations?

  • Gas chromatography (GC or GC‑MS)
  • Flame photometry
  • Polarimetry only
  • Atomic absorption spectroscopy

Correct Answer: Gas chromatography (GC or GC‑MS)

Q9. What functional group difference distinguishes menthol from menthone?

  • Menthol is an alcohol; menthone is a ketone
  • Menthol is a phenol; menthone is an ether
  • Menthol is a carboxylic acid; menthone is an ester
  • Menthol is an aldehyde; menthone is an amine

Correct Answer: Menthol is an alcohol; menthone is a ketone

Q10. Which biosynthetic precursor leads to menthol in plants?

  • Geranyl diphosphate (GPP)
  • Acetyl‑CoA directly
  • Shikimate
  • Malonyl‑CoA oligomer

Correct Answer: Geranyl diphosphate (GPP)

Q11. Which industrial method is typically used to isolate menthol from peppermint oil?

  • Steam distillation followed by fractional distillation
  • Soxhlet extraction with water
  • Electrochemical deposition
  • Supercritical CO2 without any distillation

Correct Answer: Steam distillation followed by fractional distillation

Q12. In pharmaceutical formulations, menthol is commonly used as:

  • A topical analgesic and cough lozenge flavoring agent
  • An antiviral nucleoside analogue
  • A systemic antihypertensive
  • A steroidal anti‑inflammatory

Correct Answer: A topical analgesic and cough lozenge flavoring agent

Q13. Menthol often enhances transdermal drug delivery by acting as a:

  • Skin penetration enhancer
  • Viscosity increasing polymer
  • pH buffering agent
  • Preservative

Correct Answer: Skin penetration enhancer

Q14. Which pharmacological action contributes to menthol’s analgesic/counterirritant effect?

  • Cooling sensation via TRPM8 activation and counterirritation
  • Direct opioid receptor agonism equivalent to morphine
  • Systemic anti‑inflammatory cytokine inhibition at microgram doses
  • Inhibition of acetylcholine release at neuromuscular junctions

Correct Answer: Cooling sensation via TRPM8 activation and counterirritation

Q15. Which reagent is commonly used in the laboratory to reduce menthone to menthol?

  • Sodium borohydride (NaBH4)
  • Potassium permanganate (KMnO4)
  • Chromic acid (H2CrO4)
  • Nitric acid (HNO3)

Correct Answer: Sodium borohydride (NaBH4)

Q16. Which quality control parameter is most indicative of menthol purity?

  • Melting point close to 34–36 °C
  • Colorless fluorescence under UV light
  • High viscosity at room temperature
  • High refractive index identical to water

Correct Answer: Melting point close to 34–36 °C

Q17. On exposure to air and light, menthol is most likely to undergo:

  • Oxidation to menthone
  • Polymerization to high‑molecular polymers
  • Hydrolysis to menthyl alcohol
  • Isomerization to glucose

Correct Answer: Oxidation to menthone

Q18. Which adverse effect can occur with large oral ingestion of menthol?

  • CNS depression and respiratory compromise
  • Immediate severe hypertension only
  • Renal tubular necrosis in microdoses
  • Irreversible blindness at therapeutic doses

Correct Answer: CNS depression and respiratory compromise

Q19. How is menthol classified for use as a flavoring agent by regulatory agencies?

  • Generally Recognized As Safe (GRAS) for specified uses
  • Prohibited in all cosmetic and food products
  • Prescription‑only API
  • Controlled substance under narcotics law

Correct Answer: Generally Recognized As Safe (GRAS) for specified uses

Q20. Which enantiomer of menthol typically gives the strongest sensory cooling?

  • (-)-Menthol (levomenthol)
  • (+)-Menthol (d‑menthol)
  • Racemate is strongest
  • Menthone is stronger than any menthol enantiomer

Correct Answer: (-)-Menthol (levomenthol)

Q21. Which derivative of menthol is often formed during formulation to modify fragrance or volatility?

  • Menthyl esters (e.g., menthyl acetate)
  • Menthyl chloride salts
  • Menthyl glycosides
  • Menthyl peptides

Correct Answer: Menthyl esters (e.g., menthyl acetate)

Q22. Which IR spectral feature would confirm the presence of the menthol OH group?

  • Broad O–H stretch around 3200–3600 cm⁻¹
  • Strong carbonyl peak at 1700 cm⁻¹ only
  • Sharp N–H stretch at 3300 cm⁻¹
  • Absence of any O–H band

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

Q23. In purity testing, a melting point significantly below 34–36 °C usually indicates:

  • Presence of impurities or a different isomer
  • Higher than expected purity
  • That the sample is actually a gas
  • Complete absence of menthol

Correct Answer: Presence of impurities or a different isomer

Q24. The conversion of menthol to a menthyl ester is an example of which reaction type?

  • Esterification (acylation of an alcohol)
  • Hydrogenation of a double bond
  • Oxidative cleavage of an ether
  • Aldol condensation

Correct Answer: Esterification (acylation of an alcohol)

Q25. Which analytical technique is specifically used to separate and quantify menthol enantiomers?

  • Chiral gas chromatography or chiral HPLC
  • Simple UV spectrophotometry without chiral selector
  • Non‑selective thin‑layer chromatography only
  • Gravimetric analysis

Correct Answer: Chiral gas chromatography or chiral HPLC

Q26. How does menthol in a throat lozenge help reduce coughing?

  • Local sensory cooling reduces cough reflex sensitivity via TRPM8 activation
  • It systemically suppresses the respiratory center in the medulla
  • It acts as a potent antiviral to eliminate cough viruses instantly
  • It produces mucus hypersecretion to trap irritants

Correct Answer: Local sensory cooling reduces cough reflex sensitivity via TRPM8 activation

Q27. Why is menthol commonly included in topical analgesic creams?

  • It provides cooling/counterirritant effects and mild analgesia
  • It acts as the primary anti‑inflammatory steroid
  • It forms a permanent skin barrier preventing absorption
  • It neutralizes all skin pathogens

Correct Answer: It provides cooling/counterirritant effects and mild analgesia

Q28. Which oxidizing reagent can convert menthol to menthone in the laboratory?

  • Chromic acid (Jones reagent)
  • Sodium borohydride (NaBH4)
  • Lithium aluminum hydride (LiAlH4)
  • Hydrogen gas with Pd/C under mild conditions

Correct Answer: Chromic acid (Jones reagent)

Q29. Optimal storage conditions for menthol to maintain stability include:

  • Cool, dark, airtight container to prevent oxidation and volatilization
  • Open exposure to air at high temperature
  • Storage in alkaline aqueous solution
  • Continuous UV irradiation to preserve fragrance

Correct Answer: Cool, dark, airtight container to prevent oxidation and volatilization

Q30. Which pharmacokinetic property best describes topical menthol?

  • High lipophilicity leading to local absorption with limited systemic exposure
  • Complete oral bioavailability above 90%
  • Excreted unchanged primarily via glomerular filtration within minutes
  • Accumulation exclusively in bone tissue

Correct Answer: High lipophilicity leading to local absorption with limited systemic exposure

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