Named Reactions: Ozonolysis and Michael addition MCQs With Answer

Introduction: Named Reactions: Ozonolysis and Michael addition MCQs With Answer is designed for M.Pharm students preparing for MPC 102T Advanced Organic Chemistry I. This set of focused multiple-choice questions covers mechanistic details, reagent choice, work-up conditions, synthetic applications and safety considerations for ozonolysis and Michael addition—two indispensable transformations in modern organic synthesis. Questions probe understanding of intermediates (molozonide, ozonide), reductive vs oxidative workups, conjugate (1,4) addition mechanisms, donor/acceptor patterns, catalytic variants and strategic uses such as Robinson annulation. Each item includes concise options and the correct answer to help reinforce learning and exam readiness.

Q1. What is the primary transformation achieved by ozonolysis of an alkene under standard reductive work-up?

• Conversion of a C=C bond to two alkyl radicals
• Hydrogenation of the double bond to give an alkane
• Oxidative cleavage of the C=C bond to give carbonyl compounds
• Isomerization of the double bond to a conjugated diene

Correct Answer: Oxidative cleavage of the C=C bond to give carbonyl compounds

Q2. Which reagent is commonly used for a reductive workup after ozonolysis to obtain aldehydes/ketones while avoiding further oxidation?

• Hydrogen peroxide (H2O2)
• Dimethyl sulfide (Me2S)
• Chromic acid (H2CrO4)
• Ozone (O3) itself

Correct Answer: Dimethyl sulfide (Me2S)

Q3. If an ozonolysis is performed with an oxidative workup, which reagent is typically used to convert initial ozonide fragments into carboxylic acids?

• Triphenylphosphine (PPh3)
• Dimethyl sulfide (Me2S)
• Hydrogen peroxide (H2O2)
• LiAlH4

Correct Answer: Hydrogen peroxide (H2O2)

Q4. What transient intermediates are formed during the mechanism of ozonolysis before final cleavage?

• Carbocations and carbanions
• Peroxides directly converted to acids
• Molozonide followed by ozonide
• Allylic radicals only

Correct Answer: Molozonide followed by ozonide

Q5. Ozonolysis of an internal, disubstituted alkene with reductive workup most commonly gives which types of products?

• A pair of alcohols
• Two aldehydes exclusively
• Two ketones or a ketone and an aldehyde depending on substitution
• A mixture of alkanes and dienes

Correct Answer: Two ketones or a ketone and an aldehyde depending on substitution

Q6. Which safety concern is most important when performing ozonolysis in the laboratory?

• Formation of highly toxic nitriles
• Generation and accumulation of unstable ozonides that can be explosive
• Extensive evolution of flammable hydrogen gas
• Production of strong acids that corrode glass

Correct Answer: Generation and accumulation of unstable ozonides that can be explosive

Q7. Which solvent and temperature combination is most commonly employed for controlled ozonolysis reactions to minimize side reactions?

• Water at 25 °C
• Methanol at 0 °C
• Cold dichloromethane (CH2Cl2) at –78 °C
• Toluene at reflux

Correct Answer: Cold dichloromethane (CH2Cl2) at –78 °C

Q8. Which statement best describes the stereochemical outcome of ozonolysis of a substituted alkene?

• Ozonolysis always preserves the original stereochemistry of the double bond
• Ozonolysis converts stereochemical information at the double bond into two separate stereocenters with predictable configuration
• Ozonolysis cleaves the double bond and yields carbonyl fragments; stereochemistry at the original double bond is not directly retained
• Ozonolysis inverts stereochemistry and produces enantiomers exclusively

Correct Answer: Ozonolysis cleaves the double bond and yields carbonyl fragments; stereochemistry at the original double bond is not directly retained

Q9. Which workup would you choose to convert an ozonide to carboxylic acids rather than aldehydes?

• Workup with zinc and acetic acid
• Workup with dimethyl sulfide
• Oxidative workup with hydrogen peroxide
• Neutral aqueous quench only

Correct Answer: Oxidative workup with hydrogen peroxide

Q10. The Michael addition is best described as which type of transformation?

• 1,2-addition of nucleophiles to carbonyl carbons
• Electrophilic aromatic substitution
• 1,4-conjugate addition of a nucleophile to an α,β-unsaturated carbonyl compound
• Radical chain polymerization

Correct Answer: 1,4-conjugate addition of a nucleophile to an α,β-unsaturated carbonyl compound

Q11. Which of the following is a classic Michael donor used to form new C–C bonds in conjugate addition?

• Grignard reagent (RMgX) attacking a carbonyl directly
• Malonate enolate (diethyl malonate-derived enolate)
• Diazonium salts
• Alkyl halides in SN2 reactions

Correct Answer: Malonate enolate (diethyl malonate-derived enolate)

Q12. Which substrate is a typical Michael acceptor?

• Allylic alcohol
• α,β-Unsaturated ketone (enone)
• Terminal alkyne lacking electron-withdrawing groups
• Simple alkane

Correct Answer: α,β-Unsaturated ketone (enone)

Q13. Mechanistically, the initial step of a typical Michael addition involves which event?

• Electrophilic attack on the α-carbon to form a carbocation
• Nucleophilic attack at the β-carbon of the α,β-unsaturated system forming an enolate intermediate
• Radical abstraction of a hydrogen atom from the donor
• Concerted pericyclic cycloaddition

Correct Answer: Nucleophilic attack at the β-carbon of the α,β-unsaturated system forming an enolate intermediate

Q14. Which statement correctly predicts conditions favoring 1,4-conjugate (Michael) addition over direct 1,2-addition to a carbonyl?

• Use of hard, strongly basic nucleophiles at very low temperature favors 1,4-addition
• Soft nucleophiles and polarizable reaction conditions favor 1,4-conjugate addition
• Presence of strong Lewis acids always prevents 1,4-addition
• High dilution always leads to 1,2-addition

Correct Answer: Soft nucleophiles and polarizable reaction conditions favor 1,4-conjugate addition

Q15. An intramolecular Michael addition is particularly useful in synthesis because it commonly leads to what outcome?

• Formation of linear oligomers exclusively
• Cyclization to form five- or six-membered rings with high efficiency
• Generation of unstable allenes only
• Only aromatic ring formation

Correct Answer: Cyclization to form five- or six-membered rings with high efficiency

Q16. The Michael reaction is named after which chemist?

• Adolf von Baeyer
• Arthur Michael
• Rudolf Willstätter
• Ernst Otto Fischer

Correct Answer: Arthur Michael

Q17. Which catalytic mode enables enantioselective Michael additions by forming an enamine from a carbonyl donor?

• Brønsted acid catalysis only
• Enamine organocatalysis using a secondary amine (e.g., proline derivatives)
• Radical photoredox catalysis exclusively
• Base-catalyzed aldol condensation without any chiral influence

Correct Answer: Enamine organocatalysis using a secondary amine (e.g., proline derivatives)

Q18. The tandem sequence combining a Michael addition followed by an intramolecular aldol condensation to construct polycyclic scaffolds is known as what?

• Wittig–Michael sequence
• Robinson annulation
• Bischler–Möhlau reaction
• Claisen rearrangement

Correct Answer: Robinson annulation

Q19. For achieving high enantioselectivity in catalytic Michael additions to chalcones (enones), which catalyst class is often employed?

• Achiral inorganic bases only
• Chiral secondary amine organocatalysts or chiral Lewis acids
• Strong oxidants like manganese dioxide
• Simple transition metals without chiral ligands

Correct Answer: Chiral secondary amine organocatalysts or chiral Lewis acids

Q20. In many Michael additions, what step is typically rate-determining under standard conditions?

• Protonation of the final product
• Formation of the enolate donor from the carbonyl compound
• Conjugate nucleophilic attack (C–C bond formation) at the β-carbon
• Diffusion of solvent molecules

Correct Answer: Conjugate nucleophilic attack (C–C bond formation) at the β-carbon

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