Structure and uses of phenanthrene MCQs With Answer

Structure and uses of phenanthrene MCQs With Answer

Phenanthrene, a tricyclic polycyclic aromatic hydrocarbon (PAH), has a rigid fused-ring structure crucial to understanding its chemical behavior, aromaticity, and reactivity. For B.Pharm students, mastering phenanthrene’s numbering, resonance stabilization, electrophilic substitution patterns, spectral signatures (NMR, IR, UV), and synthetic transformations is vital for drug design and organic synthesis. Phenanthrene derivatives appear as intermediates in pharmaceutical scaffolds, dyes, and organic materials, while toxicity and environmental persistence are important in pharmacology and safety assessments. This set emphasizes structural concepts, reaction mechanisms, spectroscopy interpretation, and practical uses. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the molecular formula of phenanthrene?

• C14H10
• C12H8
• C16H12
• C10H8

Correct Answer: C14H10

Q2. Which description best defines the connectivity of rings in phenanthrene?

• Three linearly fused benzene rings
• Three angularly fused benzene rings forming a bent shape
• Two benzene rings fused with a cyclopentane
• A benzene ring fused with a naphthalene at the 2,3-positions

Correct Answer: Three angularly fused benzene rings forming a bent shape

Q3. According to IUPAC numbering, which carbon is designated C9 in phenanthrene?

• One of the bridgehead carbons between rings
• The central ring carbon adjacent to the 10-position
• A terminal carbon on the outer ring farthest from the central ring
• The carbon in the middle of the central ring opposite the bay region

Correct Answer: The central ring carbon adjacent to the 10-position

Q4. Which positions on phenanthrene are most susceptible to electrophilic substitution?

• 9 and 10 positions (alpha positions)
• 1 and 2 positions (peri positions)
• 3 and 4 positions
• All positions are equally reactive

Correct Answer: 9 and 10 positions (alpha positions)

Q5. Phenanthrene is more thermodynamically stable than which isomeric PAH due to resonance stabilization?

• Anthracene
• Naphthalene
• Phenol
• Fluorene

Correct Answer: Anthracene

Q6. Which concept explains the extra stability of phenanthrene compared to linear isomers?

• Clar’s aromatic sextet theory
• Bredt’s rule
• Markovnikov’s rule
• Hammond’s postulate

Correct Answer: Clar’s aromatic sextet theory

Q7. In 1H NMR spectroscopy, protons at the 9 and 10 positions of phenanthrene typically appear:

• Downfield (deshielded) relative to other aromatic protons
• Upfield (shielded) relative to other aromatic protons
• As a broad exchangeable singlet
• Not observed due to rapid exchange

Correct Answer: Downfield (deshielded) relative to other aromatic protons

Q8. Which of the following is a common oxidation product when phenanthrene is oxidized at the 9,10-positions?

• Phenanthrene-9,10-dione (phenanthrenequinone)
• Phenanthrol (alcohol at C1)
• Phenanthrene sulfone
• Phenanthrene epoxide at C3-C4

Correct Answer: Phenanthrene-9,10-dione (phenanthrenequinone)

Q9. The bay region of phenanthrene refers to which structural feature?

• The concave region between rings creating a sterically hindered site (positions 9 and 10)
• The exterior edge of the terminal benzene ring
• The carbonyl region when oxidized
• The substituents at 1 and 8 positions

Correct Answer: The concave region between rings creating a sterically hindered site (positions 9 and 10)

Q10. Which reaction is commonly used to hydrogenate phenanthrene to tetrahydrophenanthrene derivatives?

• Catalytic hydrogenation with Pd/C or Pt catalyst
• Birch reduction using sodium in liquid ammonia
• Radical halogenation followed by substitution
• Nucleophilic aromatic substitution with strong base

Correct Answer: Catalytic hydrogenation with Pd/C or Pt catalyst

Q11. Which UV–Vis characteristic is typical of phenanthrene compared to benzene?

• Bathochromic shift and stronger π→π* transitions due to extended conjugation
• Hypsochromic shift due to decreased conjugation
• No UV absorption above 200 nm
• Only n→π* transitions are observed

Correct Answer: Bathochromic shift and stronger π→π* transitions due to extended conjugation

Q12. In mass spectrometry, a common fragmentation pattern for phenanthrene includes:

• Loss of a hydrogen radical leading to [M-1]+ peak
• Cleavage giving stable phenyl cation fragments
• Extensive fragmentation to aliphatic fragments only
• Formation of a stable M+2 isotope peak as the base peak

Correct Answer: Cleavage giving stable phenyl cation fragments

Q13. Which position substitution generally leads to stabilization by resonance and is favored in electrophilic substitution?

• 9-position
• 4-position
• 2-position
• 5-position

Correct Answer: 9-position

Q14. Phenanthrene derivatives are used in pharmaceuticals mainly as:

• Aromatic scaffolds for hydrophobic core and π–π interactions
• Highly water-soluble drug carriers
• Sugar-mimicking hydrophilic moieties
• Primary active-site metal chelators

Correct Answer: Aromatic scaffolds for hydrophobic core and π–π interactions

Q15. The formation of phenanthrene from simpler aromatic molecules in synthesis often involves which key step?

• Intramolecular cyclization (e.g., oxidative cyclodehydrogenation)
• Nucleophilic aromatic substitution
• Alkyl halide elimination
• Hydrolysis of esters

Correct Answer: Intramolecular cyclization (e.g., oxidative cyclodehydrogenation)

Q16. Which reagent is commonly used for selective oxidation at the 9,10-positions to give 9,10-dione?

• Chromium(VI) reagents like PCC or KMnO4 under controlled conditions
• Sodium borohydride (NaBH4)
• Hydrochloric acid at high temperature
• Trimethylsilyl chloride (TMSCl)

Correct Answer: Chromium(VI) reagents like PCC or KMnO4 under controlled conditions

Q17. Which statement about aromaticity in phenanthrene is correct?

• Phenanthrene contains localized aromatic sextets and shows global aromatic stabilization
• Phenanthrene is non-aromatic due to ring strain
• All carbons in phenanthrene are sp3 hybridized
• Phenanthrene violates Hückel’s rule

Correct Answer: Phenanthrene contains localized aromatic sextets and shows global aromatic stabilization

Q18. What is a significant toxicological concern associated with phenanthrene and its derivatives?

• Potential genotoxicity and persistence as PAH environmental pollutants
• Immediate corrosive damage on skin contact only
• Rapid biodegradability making them non-toxic
• High acute nutritional value

Correct Answer: Potential genotoxicity and persistence as PAH environmental pollutants

Q19. Which mechanism typically explains electrophilic aromatic substitution on phenanthrene?

• Formation of a σ-complex (arenium ion) stabilized by resonance across adjacent rings
• Radical chain propagation without σ-complex formation
• Nucleophilic addition-elimination pathway
• Concerted pericyclic substitution

Correct Answer: Formation of a σ-complex (arenium ion) stabilized by resonance across adjacent rings

Q20. In retrosynthetic analysis of a phenanthrene-containing drug, which disconnection is commonly considered?

• Disconnecting to two substituted benzene fragments followed by intramolecular cyclodehydrogenation
• Cleavage into aliphatic fragments only
• Isolating a single aromatic ring as the only building block
• Converting phenanthrene directly into amino acids

Correct Answer: Disconnecting to two substituted benzene fragments followed by intramolecular cyclodehydrogenation

Q21. Which spectral feature in IR spectroscopy helps confirm aromatic C–H in phenanthrene?

• Weak bands around 3000–3100 cm−1 corresponding to aromatic C–H stretch
• A strong broad O–H stretch at 3400 cm−1
• Sharp nitrile peak at 2200 cm−1
• Strong carbonyl band at 1700 cm−1 always present

Correct Answer: Weak bands around 3000–3100 cm−1 corresponding to aromatic C–H stretch

Q22. Which property of phenanthrene contributes to its use in organic electronic materials?

• Planar conjugated π-system enabling charge transport and π–π stacking
• High aqueous solubility for electrolyte applications
• Ability to chelate transition metals strongly
• Extremely high acidity

Correct Answer: Planar conjugated π-system enabling charge transport and π–π stacking

Q23. Peri-substitution in phenanthrene refers to substitution at which pair of positions?

• 1 and 8 positions located on adjacent rings across the bay
• 9 and 10 positions only
• 2 and 3 positions on the same ring
• 4 and 5 positions separated by a double bond

Correct Answer: 1 and 8 positions located on adjacent rings across the bay

Q24. The aromatic stabilization energy of phenanthrene arises mainly from:

• Delocalized π-electrons distributed over fused rings and resonance structures
• Strong σ-bonding only
• Hydrogen bonding between rings
• Ionic interactions within the molecule

Correct Answer: Delocalized π-electrons distributed over fused rings and resonance structures

Q25. Which is a common synthetic precursor used to build the phenanthrene core in the laboratory?

• Biaryl intermediates formed by Suzuki–Miyaura coupling followed by cyclization
• Simple alkanes directly cyclized without functionalization
• Unsubstituted benzene only, fused by heating
• Sugars converted to aromatics in one step

Correct Answer: Biaryl intermediates formed by Suzuki–Miyaura coupling followed by cyclization

Q26. Which derivative is formed by bromination at the 9-position under radical conditions?

• 9-bromophenanthrene
• 1-bromophenanthrene exclusively
• 9,10-dibromophenanthrene exclusively
• Phenanthrene oxide

Correct Answer: 9-bromophenanthrene

Q27. In terms of Möbius vs Hückel aromaticity, phenanthrene follows which rule for π-electron count in each aromatic sextet?

• Hückel’s rule (4n+2 π electrons for each aromatic sextet)
• Möbius rule (4n π electrons for aromaticity)
• No rule applies to fused systems
• Only antiaromatic criteria apply

Correct Answer: Hückel’s rule (4n+2 π electrons for each aromatic sextet)

Q28. Which functional group introduction at C9 is commonly used to further functionalize phenanthrene for drug synthesis?

• Carbonyl (9-oxo) group enabling further nucleophilic addition or condensation
• Silyl ether providing hydrophilicity
• Phosphate ester improving lipophilicity
• Thioether exclusively for hydrogen bonding

Correct Answer: Carbonyl (9-oxo) group enabling further nucleophilic addition or condensation

Q29. Which statement about peri-hydrogen interactions in phenanthrene is correct?

• Hydrogens at peri positions (1 and 8) experience steric crowding leading to higher chemical shifts
• Peri hydrogens always form hydrogen bonds with solvent
• Peri positions are free of steric effects and highly reactive
• Peri hydrogens are sp3 and thus non-aromatic

Correct Answer: Hydrogens at peri positions (1 and 8) experience steric crowding leading to higher chemical shifts

Q30. Photochemical reactions of phenanthrene commonly lead to which type of transformation?

• Photochemical cycloaddition or photooxidation forming oxygenated products
• Thermal isomerization without light
• Complete polymerization only under dark conditions
• Spontaneous hydration to alcohols

Correct Answer: Photochemical cycloaddition or photooxidation forming oxygenated products

Q31. Which reagent would you choose for selective electrophilic nitration of phenanthrene with control over regiochemistry?

• Nitronium generated from nitric acid and acetic anhydride under low temperature
• Strong base such as NaNH2 in liquid ammonia
• Hydrogen peroxide without acid
• Lewis acid-free nitration using nitrosonium salts only

Correct Answer: Nitronium generated from nitric acid and acetic anhydride under low temperature

Q32. Which structural feature distinguishes phenanthrene from anthracene?

• Angular fusion of rings in phenanthrene versus linear fusion in anthracene
• Presence of a heteroatom in phenanthrene only
• Phenanthrene has no aromaticity while anthracene is aromatic
• Anthracene is cyclic and phenanthrene is acyclic

Correct Answer: Angular fusion of rings in phenanthrene versus linear fusion in anthracene

Q33. In designing a drug molecule incorporating phenanthrene, what pharmacokinetic concern is most relevant?

• Low aqueous solubility and high lipophilicity affecting bioavailability
• Excessive ionization in blood at physiological pH
• Immediate renal elimination due to high polarity
• Complete metabolic inertness making clearance impossible

Correct Answer: Low aqueous solubility and high lipophilicity affecting bioavailability

Q34. Which computational concept helps predict regioselectivity of electrophilic attack on phenanthrene?

• Frontier molecular orbital (FMO) theory evaluating HOMO coefficients
• Pauling electronegativity scale exclusively
• Simple bond dissociation energies only
• Boiling point comparisons

Correct Answer: Frontier molecular orbital (FMO) theory evaluating HOMO coefficients

Q35. Which structural isomer can interconvert from phenanthrene under harsh conditions?

• Anthracene via isomerization under certain high-energy conditions
• Benzene by simple heating
• Naphthalene by one-step reduction
• Fluorene by hydration

Correct Answer: Anthracene via isomerization under certain high-energy conditions

Q36. Which safety measure is most important when handling phenanthrene in the lab?

• Use of gloves and fume hood to avoid inhalation and dermal exposure due to PAH toxicity
• Only UV shielding is required
• No special precautions; phenanthrene is non-hazardous
• Only refrigeration is necessary for safety

Correct Answer: Use of gloves and fume hood to avoid inhalation and dermal exposure due to PAH toxicity

Q37. Which reagent is suitable for introducing a nitro group at an activated position of phenanthrene?

• Nitration mixture: concentrated HNO3 and concentrated H2SO4
• NaBH4 in methanol
• Potassium tert-butoxide in DMSO
• Grignard reagent without electrophile

Correct Answer: Nitration mixture: concentrated HNO3 and concentrated H2SO4

Q38. Which property of phenanthrene affects its environmental fate?

• Low water solubility and high persistence leading to bioaccumulation
• High volatility making it instantly evaporate
• Readily biodegradable making it non-persistent
• Strong ionic character leading to easy dispersion in water

Correct Answer: Low water solubility and high persistence leading to bioaccumulation

Q39. Which type of derivative of phenanthrene is commonly used as a dye intermediate?

• Substituted phenanthrenes bearing electron-donating or -withdrawing groups to tune color
• Fully saturated phenanthrene with no conjugation
• Simple alkyl-substituted benzene only
• Carbohydrate-conjugated phenanthrene exclusively

Correct Answer: Substituted phenanthrenes bearing electron-donating or -withdrawing groups to tune color

Q40. Which position pair forms the so-called “bay region” that is reactive towards oxidation and epoxidation?

• 9 and 10 positions
• 1 and 2 positions
• 3 and 4 positions
• 5 and 6 positions

Correct Answer: 9 and 10 positions

Q41. Which reaction would convert phenanthrene to a dihydro derivative selectively?

• Partial catalytic hydrogenation under controlled pressure and temperature
• Complete combustion in air
• Acid-catalyzed hydration to give diols directly
• Radical polymerization with peroxides

Correct Answer: Partial catalytic hydrogenation under controlled pressure and temperature

Q42. How does substitution at the 2-position affect reactivity at the 9-position in phenanthrene?

• Electron-donating substituents at C2 can direct and enhance electrophilic attack at C9 via resonance
• Substitution at C2 has no electronic or steric influence
• Only halogen at C2 can deactivate C9 by hydrogen bonding
• C2 substitution converts the molecule to aliphatic hydrocarbon

Correct Answer: Electron-donating substituents at C2 can direct and enhance electrophilic attack at C9 via resonance

Q43. Which of the following best describes the HOMO distribution in phenanthrene relevant to electrophilic attack?

• HOMO density is higher at the 9 and 10 positions favoring electrophilic attack there
• HOMO is entirely localized on peripheral hydrogens only
• HOMO distribution forbids any substitution on the central ring
• HOMO density is maximal at carbonyl carbons only

Correct Answer: HOMO density is higher at the 9 and 10 positions favoring electrophilic attack there

Q44. Which synthetic transformation converts phenanthrene into functionalized derivatives via C–H activation?

• Transition-metal-catalyzed C–H activation (e.g., Pd-catalyzed direct arylation)
• Direct nucleophilic substitution at sp3 carbons only
• Hydrolysis of aromatic ring under mild conditions
• Electrolysis in pure water without electrodes

Correct Answer: Transition-metal-catalyzed C–H activation (e.g., Pd-catalyzed direct arylation)

Q45. Which hydrogenation pattern yields 9,10-dihydrophenanthrene specifically?

• Selective hydrogenation of the central ring double bonds while leaving outer rings aromatic
• Hydrogenation of all three rings to give perhydrophenanthrene
• Hydrogenation only at terminal carbons to give allylic alcohols
• Ozonolysis followed by reduction

Correct Answer: Selective hydrogenation of the central ring double bonds while leaving outer rings aromatic

Q46. Which oxidative enzymatic pathway in the environment commonly transforms phenanthrene?

• Microbial dioxygenase-mediated oxidation producing dihydrodiols and further metabolites
• Spontaneous combustion to CO2 only
• Direct photolytic conversion to sugars
• Enzymatic phosphorylation to give water-soluble salts

Correct Answer: Microbial dioxygenase-mediated oxidation producing dihydrodiols and further metabolites

Q47. What is a key synthetic challenge when preparing substituted phenanthrenes for drug leads?

• Regioselective functionalization of closely similar aromatic positions without overreaction
• Breaking a single carbon-carbon bond selectively in alkanes
• Always obtaining complete solubility in water
• Converting phenanthrene into sugars directly

Correct Answer: Regioselective functionalization of closely similar aromatic positions without overreaction

Q48. Which method can be used to distinguish phenanthrene from anthracene experimentally?

• UV–Vis spectroscopy: different absorption maxima due to differing conjugation patterns
• Melting point measurement alone is always conclusive
• Both have identical NMR spectra so cannot be distinguished
• Both are colorless gases at room temperature

Correct Answer: UV–Vis spectroscopy: different absorption maxima due to differing conjugation patterns

Q49. In a medicinal chemistry context, why might a phenanthrene core be modified to reduce toxicity?

• Introduce polar substituents to lower lipophilicity and improve clearance
• Increase hydrophobic surface area to enhance persistence
• Convert aromatic core into pure hydrocarbon chains only
• Remove all heteroatoms to increase metabolic stability indefinitely

Correct Answer: Introduce polar substituents to lower lipophilicity and improve clearance

Q50. Which analytical technique provides site-specific information about proton environments in phenanthrene to deduce substitution patterns?

• 1H and 13C NMR spectroscopy including NOE and coupling constant analysis
• Simple refractive index measurement
• Gravimetric analysis only
• Basic pH titration

Correct Answer: 1H and 13C NMR spectroscopy including NOE and coupling constant analysis

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.

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