Rearrangement reactions: mechanisms and synthetic applications MCQs With Answer

Rearrangement reactions are central to advanced organic synthesis and form a critical part of the M.Pharm curriculum. This quiz-focused blog on “Rearrangement reactions: mechanisms and synthetic applications MCQs With Answer” offers targeted practice for postgraduate students preparing for MPC 102T Advanced Organic Chemistry I. Each question probes mechanistic detail, key intermediates, regiochemical and stereochemical outcomes, and industrial applications of classic rearrangements such as Baeyer–Villiger, Beckmann, Curtius, Wagner–Meerwein, Claisen, Cope, pinacol, benzilic and others. Carefully designed distractors test conceptual understanding rather than rote memory, and concise answers reinforce correct reasoning. Use this set to identify weaknesses and deepen mastery of transformation logic and synthetic utility.

Q1. In the Baeyer–Villiger oxidation, which type of substituent generally exhibits the highest migratory aptitude?

• Tertiary alkyl group
• Primary alkyl group
• Phenyl group
• Methyl group

Correct Answer: Tertiary alkyl group

Q2. The key reactive intermediate formed during the acid-catalyzed pinacol rearrangement (vicinal diol → ketone) is best described as:

• A stabilized carbocation formed after protonation and loss of water
• A peroxyacetal (Criegee-type) intermediate
• An acyl azide intermediate
• An ammonium ylide

Correct Answer: A stabilized carbocation formed after protonation and loss of water

Q3. Wagner–Meerwein rearrangements typically proceed by which sequence of events?

• Formation of a radical followed by concerted [1,2]-shift
• Formation of a carbocation followed by 1,2-alkyl or hydride shifts
• Pericyclic [3,3]-sigmatropic migration without ionic intermediates
• Nucleophilic substitution at sp2 carbon

Correct Answer: Formation of a carbocation followed by 1,2-alkyl or hydride shifts

Q4. The Claisen rearrangement is best classified mechanistically as:

• A stepwise ionic rearrangement through a carbocation
• A radical chain reaction
• A concerted [3,3]-sigmatropic pericyclic reaction (suprafacial)
• An SN2′ nucleophilic substitution

Correct Answer: A concerted [3,3]-sigmatropic pericyclic reaction (suprafacial)

Q5. In the Beckmann rearrangement of an oxime to an amide, which group migrates during the rearrangement?

• The group cis to the oxime OH
• The group anti to the oxime OH
• The hydroxyl group itself
• A hydrogen from the oxime nitrogen

Correct Answer: The group anti to the oxime OH

Q6. Which reagent is most commonly used to effect Baeyer–Villiger oxidations in laboratory synthesis?

• KMnO4
• meta-Chloroperoxybenzoic acid (mCPBA)
• Ozone (O3)
• Hydrazine hydrate

Correct Answer: meta-Chloroperoxybenzoic acid (mCPBA)

Q7. The Curtius rearrangement of an acyl azide proceeds via which reactive intermediate before trapping to give amines or ureas?

• A nitrene intermediate
• An isocyanate intermediate
• An acylium ion
• An aziridine intermediate

Correct Answer: An isocyanate intermediate

Q8. Which set of reagents is classically required for the Hofmann rearrangement (degradation) of a primary amide to an amine with one fewer carbon?

• Br2 and NaOH (bromine in base)
• PCl5 and heat
• H2/Pd (hydrogenation)
• LiAlH4 in ether

Correct Answer: Br2 and NaOH (bromine in base)

Q9. The benzilic acid rearrangement converts an α-diketone into an α-hydroxycarboxylic acid via which type of 1,2-migration?

• 1,2-hydride shift
• 1,2-alkyl shift of a primary alkyl group
• 1,2-phenyl (aryl) migration under basic conditions
• Concerted [3,3]-sigmatropic rearrangement

Correct Answer: 1,2-phenyl (aryl) migration under basic conditions

Q10. The Fries rearrangement of aryl esters to give hydroxyaryl ketones is typically catalyzed by which Lewis acid?

• AlCl3 (aluminum chloride)
• BF3·OEt2 (boron trifluoride etherate)
• Pd/C (palladium on carbon)
• NaBH4 (sodium borohydride)

Correct Answer: AlCl3 (aluminum chloride)

Q11. The oxy-Cope rearrangement is dramatically accelerated under which condition to produce enones or enolates?

• Free-radical initiators at low temperature
• Formation of the alkoxide (strong base) and heating
• Photochemical UV irradiation in neutral media
• Acid catalysis with H2SO4

Correct Answer: Formation of the alkoxide (strong base) and heating

Q12. The peroxyhemiketal-like intermediate formed during Baeyer–Villiger oxidation is commonly called the:

• Wagner intermediate
• Criegee intermediate
• Schmidt aziridinium
• Sommelet complex

Correct Answer: Criegee intermediate

Q13. Which rearrangement is synthetically useful for converting carboxylic acids into primary amines (via an acyl azide) with retention of carbon framework?

• Beckmann rearrangement
• Curtius rearrangement
• Baeyer–Villiger oxidation
• Benzilic acid rearrangement

Correct Answer: Curtius rearrangement

Q14. The industrial production of ε-caprolactam (for Nylon-6) from cyclohexanone involves which rearrangement of the corresponding oxime?

• Wagner–Meerwein rearrangement
• Beckmann rearrangement
• Claisen rearrangement
• Buchner ring expansion

Correct Answer: Beckmann rearrangement

Q15. The Wolff rearrangement of α-diazoketones upon photolysis or thermolysis primarily yields which reactive species that can be trapped to form carboxylic derivatives?

• Ketene
• Nitrene
• Carbene
• Isocyanate

Correct Answer: Ketene

Q16. The Stevens rearrangement of quaternary ammonium salts involves which key species/mechanistic proposal?

• An ammonium ylide (carbanion or ylide intermediate) that effects a 1,2-shift
• A concerted [3,3]-sigmatropic pericyclic pathway
• A peroxyacid-mediated oxygen transfer
• Direct nucleophilic aromatic substitution

Correct Answer: An ammonium ylide (carbanion or ylide intermediate) that effects a 1,2-shift

Q17. The Neber rearrangement transforms an α-oximino ketone (tosylated oxime) into which class of useful products?

• α-Hydroxy acids
• α-Aminoketones
• Carboxylic acids
• Enones via dehydration

Correct Answer: α-Aminoketones

Q18. The Cope rearrangement is specifically a [3,3]-sigmatropic rearrangement of what type of substrate?

• Allyl vinyl ethers
• 1,5-dienes (conjugated dienes with a 1,5 relationship)
• α-Diazoketones
• Aryl oximes

Correct Answer: 1,5-dienes (conjugated dienes with a 1,5 relationship)

Q19. In rearrangements like pinacol-pinacolone, which factor most strongly determines which group migrates (i.e., which 1,2-shift occurs)?

• The size (steric bulk) of migrating group only
• The electronic ability of the migrating group to stabilize the developing positive charge (carbocation stability)
• The solvent polarity exclusively
• The presence of radical initiators

Correct Answer: The electronic ability of the migrating group to stabilize the developing positive charge (carbocation stability)

Q20. The Schmidt reaction (acid-induced reaction of hydrazoic acid with carbonyl compounds) commonly provides which type of transformation?

• Conversion of ketones to tertiary alcohols
• Conversion of carboxylic acids to primary amines with loss of CO2
• Conversion of ketones to amines or amides via nitrogen insertion (R–C→R–N shift)
• Oxidation of alcohols to carbonyls

Correct Answer: Conversion of ketones to amines or amides via nitrogen insertion (R–C→R–N shift)

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