Reduction MCQs With Answer

Reduction MCQs With Answer

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Reduction MCQs With Answer cover essential reduction reactions and concepts for B.Pharm students, linking organic chemistry to drug metabolism, formulation and medicinal chemistry. This focused set emphasizes hydride reagents (NaBH4, LiAlH4, NaBH3CN), catalytic hydrogenation (Pd/C, poisoned catalysts), stereoselective methods (CBS, Luche), transfer hydrogenation, and specialized reductions (MPV, Birch, Wolff‑Kishner, Clemmensen). It also addresses enzymatic and microbial reductive biotransformations (nitroreductases, azoreductases), redox potentials, analytical monitoring and safety considerations in pharmaceutical development. These MCQs deepen mechanistic understanding and practical choices in synthesis and metabolism. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which reagent is a mild, selective hydride donor commonly used to reduce aldehydes and ketones to alcohols in protic solvents?

  • Sodium borohydride (NaBH4)
  • Lithium aluminum hydride (LiAlH4)
  • Pd/C with H2
  • Raney nickel

Correct Answer: Sodium borohydride (NaBH4)

Q2. Which reducing agent is strong enough to reduce esters, carboxylic acids and amides to alcohols or amines and must be handled under anhydrous conditions?

  • Sodium borohydride (NaBH4)
  • Lithium aluminum hydride (LiAlH4)
  • Sodium cyanoborohydride (NaBH3CN)
  • Ammonium formate with Pd/C

Correct Answer: Lithium aluminum hydride (LiAlH4)

Q3. Which catalyst is most widely used for catalytic hydrogenation of C=C and C=O bonds under molecular hydrogen in organic synthesis?

  • Pd/C (palladium on carbon)
  • LiAlH4
  • NaBH4
  • Aluminum isopropoxide

Correct Answer: Pd/C (palladium on carbon)

Q4. Which named reduction converts carbonyl compounds into methylene groups using hydrazine and strong base (high temperature)?

  • Clemmensen reduction
  • Wolff–Kishner reduction
  • Meerwein–Ponndorf–Verley (MPV) reduction
  • Birch reduction

Correct Answer: Wolff–Kishner reduction

Q5. In biological systems, which enzyme class commonly catalyzes the reduction of nitro groups in xenobiotics to corresponding amines?

  • Nitroreductases
  • Aldehyde dehydrogenases
  • Cytochrome P450 monooxygenases
  • Transferases

Correct Answer: Nitroreductases

Q6. Which reagent is most appropriate for reductive amination of aldehydes/ketones to secondary amines under mildly acidic to neutral conditions?

  • Sodium cyanoborohydride (NaBH3CN)
  • Lithium aluminum hydride (LiAlH4)
  • Hydrogen with Pd/C
  • Sodium borohydride (NaBH4)

Correct Answer: Sodium cyanoborohydride (NaBH3CN)

Q7. The Corey–Bakshi–Shibata (CBS) reduction achieves high enantioselectivity by using which type of catalyst?

  • Chiral oxazaborolidine catalyst
  • Chiral rhodium complex
  • Chiral aluminum hydride
  • Chiral organocopper reagent

Correct Answer: Chiral oxazaborolidine catalyst

Q8. Which reduction uses a secondary alcohol (e.g., isopropanol) and aluminum alkoxide as a hydride-transfer system to reduce ketones reversibly?

  • Meerwein–Ponndorf–Verley (MPV) reduction
  • Clemmensen reduction
  • Birch reduction
  • Wolff–Kishner reduction

Correct Answer: Meerwein–Ponndorf–Verley (MPV) reduction

Q9. Which reduction employs alkali metals in liquid ammonia to partially reduce aromatic rings to 1,4-dienes?

  • Birch reduction
  • Clemmensen reduction
  • Hydrogenation with Pd/C
  • MPV reduction

Correct Answer: Birch reduction

Q10. Which acidic reduction using zinc amalgam (Zn(Hg)) and HCl reduces carbonyls to methylene groups and is compatible with many aromatic systems?

  • Clemmensen reduction
  • Wolff–Kishner reduction
  • MPV reduction
  • Luche reduction

Correct Answer: Clemmensen reduction

Q11. Which reagent is commonly used to reduce disulfide bonds to free thiols in biochemical and formulation studies?

  • Dithiothreitol (DTT)
  • Iodine
  • Hydrogen peroxide
  • Sodium borohydride

Correct Answer: Dithiothreitol (DTT)

Q12. Which electrochemical parameter is most useful to predict whether a drug molecule will undergo reduction under biological or electrochemical conditions?

  • Standard reduction potential (E°)
  • pKa
  • Optical rotation
  • Partition coefficient (log P)

Correct Answer: Standard reduction potential (E°)

Q13. Which poisoned catalyst is used for selective hydrogenation (e.g., to stop at an alkene and avoid full saturation) and improves chemoselectivity?

  • Lindlar catalyst
  • Raney nickel
  • Pd/C (fresh, active)
  • PtO2 (Adam’s catalyst)

Correct Answer: Lindlar catalyst

Q14. Which cofactor commonly donates hydride equivalents in enzymatic reductions involved in drug metabolism?

  • NADPH
  • ATP
  • Coenzyme A (CoA)
  • FADH2 (as free cofactor)

Correct Answer: NADPH

Q15. In reductive amination, what is the reactive intermediate formed from a carbonyl and an amine before reduction?

  • Imine (Schiff base)
  • Enolate
  • Radical cation
  • Acetal

Correct Answer: Imine (Schiff base)

Q16. Which approach avoids the use of gaseous hydrogen by using a hydrogen donor (like isopropanol or formate) and a catalyst to perform reductions?

  • Catalytic transfer hydrogenation
  • Direct hydride addition (LiAlH4)
  • Electrochemical oxidation
  • Photochemical oxidation

Correct Answer: Catalytic transfer hydrogenation

Q17. Which statement about lithium aluminum hydride (LiAlH4) is FALSE?

  • LiAlH4 reacts violently with water and must be used under anhydrous conditions.
  • LiAlH4 is compatible with protic solvents like methanol without hazards.
  • LiAlH4 reduces esters to primary alcohols.
  • LiAlH4 can reduce amides and nitriles to amines.

Correct Answer: LiAlH4 is compatible with protic solvents like methanol without hazards.

Q18. Which factors influence the stereochemical outcome when reducing a prochiral ketone to a secondary alcohol?

  • Chiral catalyst, substrate sterics and neighboring stereocenters
  • Only the catalyst
  • Only the solvent polarity
  • Only the temperature

Correct Answer: Chiral catalyst, substrate sterics and neighboring stereocenters

Q19. Which of the following transformations is LiAlH4 generally NOT used to perform?

  • Hydrogenation of isolated alkenes (C=C) to alkanes
  • Reduction of esters to alcohols
  • Reduction of nitriles to primary amines
  • Reduction of amides to amines

Correct Answer: Hydrogenation of isolated alkenes (C=C) to alkanes

Q20. When monitoring an enzymatic nitro-reduction assay in vitro, which analytical signal is commonly measured to follow NADPH-dependent reduction?

  • Decrease in NADPH absorbance at 340 nm
  • Increase in fluorescence at 520 nm
  • Change in pH by titration
  • Increase in turbidity

Correct Answer: Decrease in NADPH absorbance at 340 nm

Q21. Which reagent is commonly employed at low temperature to reduce esters selectively to aldehydes (stopping at aldehyde stage)?

  • Diisobutylaluminum hydride (DIBAL-H) at −78°C
  • Sodium borohydride (NaBH4) at room temperature
  • Lithium aluminum hydride (LiAlH4) at reflux
  • Ammonium formate with Pd/C

Correct Answer: Diisobutylaluminum hydride (DIBAL-H) at −78°C

Q22. The Birch reduction mechanism proceeds predominantly by which fundamental step?

  • Single-electron transfer (SET) to form radical anions
  • Hydride transfer from borohydride
  • Protonation followed by nucleophilic attack
  • Concerted pericyclic electron shift

Correct Answer: Single-electron transfer (SET) to form radical anions

Q23. Microbial reduction of azo bonds in certain prodrugs in the colon is primarily catalyzed by which activity?

  • Azoreductase activity from gut microbiota
  • Esterase activity in plasma
  • UDP‑glucuronosyltransferase in liver
  • Cytochrome oxidase in mitochondria

Correct Answer: Azoreductase activity from gut microbiota

Q24. Which protecting group on an alcohol is typically cleaved by catalytic hydrogenation (hydrogenolysis) but remains intact under NaBH4 reduction?

  • Benzyl (Bn) ether
  • Tert‑butyldimethylsilyl (TBDMS) ether
  • Acetyl (Ac) ester
  • Methoxymethyl (MOM) ether

Correct Answer: Benzyl (Bn) ether

Q25. In the Meerwein–Ponndorf–Verley (MPV) reduction the common hydrogen donor is which alcohol?

  • Isopropanol
  • Methanol
  • Ethanol
  • Tert‑butanol

Correct Answer: Isopropanol

Q26. Which reagent pair is often used as a hydrogen source for catalytic transfer hydrogenation in synthetic labs (hydrogen donor plus catalyst)?

  • Ammonium formate with Pd/C
  • LiAlH4 in ether
  • NaBH4 in water
  • H2 gas at 50 bar with Rh

Correct Answer: Ammonium formate with Pd/C

Q27. Which named reduction converts a carbonyl to a methylene using hydrazine and strong base (opposite acidity conditions to Clemmensen)?

  • Wolff–Kishner reduction
  • Birch reduction
  • Meerwein–Ponndorf–Verley reduction
  • Luche reduction

Correct Answer: Wolff–Kishner reduction

Q28. Which protocol favors 1,2-reduction of α,β‑unsaturated ketones to allylic alcohols using NaBH4 in the presence of a lanthanide salt?

  • Luche reduction (NaBH4/CeCl3)
  • MPV reduction
  • Birch reduction
  • Clemmensen reduction

Correct Answer: Luche reduction (NaBH4/CeCl3)

Q29. Which hydride reagent is considered safer and more tolerant of protic solvents and mild aqueous workups in many pharmaceutical labs?

  • Sodium borohydride (NaBH4)
  • Lithium aluminum hydride (LiAlH4)
  • Sodium metal in ethanol
  • Diisobutylaluminum hydride (DIBAL‑H)

Correct Answer: Sodium borohydride (NaBH4)

Q30. Which electrochemical technique is commonly used to determine reduction potentials and redox behavior of drug candidates?

  • Cyclic voltammetry
  • Nuclear magnetic resonance (NMR)
  • Infrared spectroscopy (IR)
  • Thin layer chromatography (TLC)

Correct Answer: Cyclic voltammetry

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