Schmidt rearrangement MCQs With Answer is an essential topic for B. Pharm students studying pharmaceutical organic chemistry and reaction mechanisms. This introduction covers Schmidt reaction definitions, variants (ketone and carboxylic acid types), key reagents like hydrazoic acid (HN3) or sodium azide with strong acid, critical intermediates (nitrilium and isocyanate), migratory aptitude concepts, and synthetic uses such as lactam formation and amine synthesis. Understanding mechanism, scope, limitations, and safety is vital for drug synthesis and process chemistry. This focused, keyword-rich overview prepares you for exam-style practice and application in medicinal chemistry. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. Which reagent is classically used in the Schmidt rearrangement of ketones to form amides?
- Hydrazoic acid (HN3) in the presence of strong acid
- Sodium borohydride (NaBH4)
- Grignard reagent (RMgBr)
- Ozone (O3)
Correct Answer: Hydrazoic acid (HN3) in the presence of strong acid
Q2. What is the primary product when a carboxylic acid undergoes the Schmidt reaction with hydrazoic acid?
- Amide without decarboxylation
- Primary amine with loss of CO2
- Alcohol via reduction
- Ketone via oxidation
Correct Answer: Primary amine with loss of CO2
Q3. Which intermediate is typically formed after loss of N2 in the Schmidt rearrangement of ketones?
- Carbocation
- Nitrilium ion
- Carbanion
- Radical
Correct Answer: Nitrilium ion
Q4. In the Schmidt rearrangement, which step directly leads to migration of an alkyl or aryl group?
- Protonation of hydrazoic acid
- Formation of azido-hydrin followed by rearrangement
- Radical abstraction
- Nucleophilic substitution at nitrogen
Correct Answer: Formation of azido-hydrin followed by rearrangement
Q5. Which of the following best describes the migratory aptitude in the Schmidt rearrangement?
- Group that best stabilizes positive charge migrates preferentially
- Smallest group migrates preferentially
- Group with highest electronegativity migrates preferentially
- Aryl groups never migrate
Correct Answer: Group that best stabilizes positive charge migrates preferentially
Q6. Which strong acid is commonly used as catalyst in laboratory Schmidt reactions?
- Sulfuric acid (H2SO4)
- Sodium hydroxide (NaOH)
- Triethylamine
- Potassium carbonate (K2CO3)
Correct Answer: Sulfuric acid (H2SO4)
Q7. Schmidt reaction of a cyclic ketone often leads to which valuable class of compounds used in pharmaceutical synthesis?
- Lactams (ring-expanded amides)
- Ethers
- Alkyl halides
- Polyenes
Correct Answer: Lactams (ring-expanded amides)
Q8. Which hazardous property of hydrazoic acid (HN3) is most relevant to lab safety during Schmidt reactions?
- It is highly explosive and toxic
- It is a strong oxidizer like peroxides
- It is an inert gas at room temperature
- It is extremely basic
Correct Answer: It is highly explosive and toxic
Q9. How does the Schmidt rearrangement of acyl azides (Curtius-like pathway) differ mechanistically from ketone Schmidt?
- Acyl azides decompose to isocyanates, while ketone Schmidt proceeds via nitrilium ions
- Acyl azides give alcohols directly, ketones always give acids
- They are identical; no mechanistic difference
- Ketone Schmidt forms free radicals, acyl azides do not
Correct Answer: Acyl azides decompose to isocyanates, while ketone Schmidt proceeds via nitrilium ions
Q10. Which solvent type is typically chosen for Schmidt rearrangements to provide acidity and solubility?
- Nonpolar hydrocarbon solvents like hexane
- Polar protic solvents or concentrated acids
- Ether solvents without acid
- Supercritical CO2
Correct Answer: Polar protic solvents or concentrated acids
Q11. Which product results from acid-catalyzed Schmidt rearrangement of 2-phenylcyclohexanone with HN3 (common synthetic transformation)?
- Ring-expanded caprolactam derivative via migration of ring carbon
- Simple ketone reduction product
- Styrene via elimination
- Bicyclic alkane
Correct Answer: Ring-expanded caprolactam derivative via migration of ring carbon
Q12. Which statement about the stereochemical outcome at the migrating carbon in Schmidt rearrangement is generally true?
- Migratory transfer is typically a concerted 1,2-shift often preserving configuration
- Migratory transfer always inverts stereochemistry via radical pathway
- Stereochemistry is always lost due to free radical intermediates
- Stereochemistry is irrelevant because migration never involves stereocenters
Correct Answer: Migratory transfer is typically a concerted 1,2-shift often preserving configuration
Q13. Which of the following is a common synthetic application of the Schmidt rearrangement in medicinal chemistry?
- Formation of lactams for β-lactam antibiotics and caprolactam precursors
- Direct formation of sulfones from alkanes
- Selective halogenation of aromatic rings
- Polymerization of ethylene
Correct Answer: Formation of lactams for β-lactam antibiotics and caprolactam precursors
Q14. Which byproduct is evolved during the key step of azide decomposition in Schmidt rearrangement?
- Hydrogen gas (H2)
- Nitrogen gas (N2)
- Oxygen gas (O2)
- Chlorine gas (Cl2)
Correct Answer: Nitrogen gas (N2)
Q15. When performing a Schmidt rearrangement using NaN3, what additional reagent is typically required?
- Strong acid to generate HN3 in situ
- Strong base like NaOH
- Organolithium reagent
- Copper catalyst
Correct Answer: Strong acid to generate HN3 in situ
Q16. Which factor most strongly influences which group migrates in a Schmidt rearrangement?
- Migratory aptitude based on ability to stabilize positive charge or develop partial cationic character
- Molecular weight of the group alone
- Color of the substrate
- Boiling point of the solvent
Correct Answer: Migratory aptitude based on ability to stabilize positive charge or develop partial cationic character
Q17. Which functional group on a substrate would generally prevent a clean Schmidt rearrangement?
- Azide or other groups that can react with acid detrimentally
- Simple alkyl chain
- Terminal alkene remote from carbonyl
- Protected alcohol that is acid-stable
Correct Answer: Azide or other groups that can react with acid detrimentally
Q18. Which named reaction is closely related to the Schmidt rearrangement when acyl azides are intermediates?
- Curtius rearrangement
- Wittig reaction
- Bayer–Villiger oxidation
- Hofmann elimination
Correct Answer: Curtius rearrangement
Q19. In intramolecular Schmidt reactions, what key structural feature enables lactam formation?
- Proximity of an azide or azidizable functionality to a carbonyl allowing migration into a ring
- Presence of an allylic hydrogen far from the carbonyl
- Lack of any leaving groups
- Aromaticity in the substrate
Correct Answer: Proximity of an azide or azidizable functionality to a carbonyl allowing migration into a ring
Q20. Which observation suggests that migration in the Schmidt rearrangement proceeds by a concerted 1,2-shift rather than a radical pathway?
- Retention of stereochemistry at the migrating center
- Formation of polymeric byproducts
- Color change to deep blue
- Requirement for radical initiators
Correct Answer: Retention of stereochemistry at the migrating center
Q21. Which of the following is a limitation of the Schmidt rearrangement in preparative organic chemistry?
- Hazardous nature of hydrazoic acid and azides
- Complete lack of reactivity with carbonyls
- Requirement for high temperature above 500 °C
- Inability to form nitrogen-containing products
Correct Answer: Hazardous nature of hydrazoic acid and azides
Q22. Which product would you expect from Schmidt rearrangement of phenylacetic acid with HN3 and acid?
- Primary benzylamine (after decarboxylative amination)
- Benzyl alcohol
- Benzoic acid
- Benzaldehyde
Correct Answer: Primary benzylamine (after decarboxylative amination)
Q23. Which spectroscopic change is most useful to monitor loss of the azide functional group during an experiment?
- Disappearance of the strong azide stretch near ~2100 cm⁻¹ in IR
- Loss of a peak at 3300 cm⁻¹ only
- Appearance of a carbonyl stretch at 4000 cm⁻¹
- Emergence of a strong NMR signal at 0 ppm
Correct Answer: Disappearance of the strong azide stretch near ~2100 cm⁻¹ in IR
Q24. Which product is most consistent with Schmidt rearrangement of a dialkyl ketone (R-CO-R’) with HN3 under acidic conditions?
- An amide where one alkyl group has migrated to nitrogen
- An ester via transesterification
- An alcohol via reduction
- An alkene via elimination
Correct Answer: An amide where one alkyl group has migrated to nitrogen
Q25. Which modification can reduce hazards associated with handling hydrazoic acid in Schmidt reactions?
- Generate azide in situ from NaN3 and acid, use dilute conditions and careful quench
- Use pure HN3 in a sealed bomb without ventilation
- Replace acid with strong base to neutralize azide
- Conduct the reaction at extremely high pressure
Correct Answer: Generate azide in situ from NaN3 and acid, use dilute conditions and careful quench
Q26. Which analytical technique can confirm formation of an amide product after Schmidt rearrangement?
- IR showing amide C=O (~1650 cm⁻¹) and N–H stretches
- UV–vis showing strong color change only
- Gas evolution measurement alone
- Mass loss on drying only
Correct Answer: IR showing amide C=O (~1650 cm⁻¹) and N–H stretches
Q27. Which description fits the role of acid in the Schmidt reaction of ketones?
- Protonates the carbonyl increasing electrophilicity and facilitates azide attack and rearrangement
- Acts as a radical initiator to abstract hydrogen
- Serves as a base to deprotonate the substrate
- Is only a solvent and has no catalytic role
Correct Answer: Protonates the carbonyl increasing electrophilicity and facilitates azide attack and rearrangement
Q28. Which product is expected when a tertiary alkyl group and an aryl group compete in migration during Schmidt rearrangement?
- The group that better stabilizes positive charge (often tertiary or resonance-stabilized aryl) migrates
- The smaller group always migrates
- Migration never occurs; reaction fails
- Only methyl groups migrate irrespective of stability
Correct Answer: The group that better stabilizes positive charge (often tertiary or resonance-stabilized aryl) migrates
Q29. Which safety precaution is essential when working with azides in pharmaceutical labs?
- Avoid heavy metal salts and shock; work behind blast shield and use dilute solutions
- Mix azides with strong oxidizers to neutralize them
- Store azides at high temperature to keep them active
- Always evaporate azide solutions to dryness
Correct Answer: Avoid heavy metal salts and shock; work behind blast shield and use dilute solutions
Q30. Which outcome is likely if water is present during the final step of a ketone Schmidt rearrangement?
- Hydrolysis of nitrilium ion to give the corresponding amide
- Formation of stable carbene
- Complete polymerization of substrate
- Immediate formation of alkyl halide
Correct Answer: Hydrolysis of nitrilium ion to give the corresponding amide
Q31. Which is a common laboratory alternative to directly handling HN3 for Schmidt reactions?
- Use sodium azide (NaN3) with a strong acid to generate HN3 in situ
- Use sodium cyanide as direct replacement
- Replace HN3 with ammonia gas at high pressure
- Use hydrogen peroxide as an azide surrogate
Correct Answer: Use sodium azide (NaN3) with a strong acid to generate HN3 in situ
Q32. Which type of migration in Schmidt rearrangement leads to ring expansion when starting from cyclic ketones?
- 1,2-shift of a ring carbon into nitrogen to give a larger lactam
- β-elimination of a hydrogen to form alkene
- Intermolecular coupling with another molecule
- Cleavage of the ring without recombination
Correct Answer: 1,2-shift of a ring carbon into nitrogen to give a larger lactam
Q33. Which structural feature on the migrating group increases its likelihood to migrate in Schmidt rearrangement?
- Ability to stabilize positive charge via hyperconjugation or resonance
- High electronegativity with no resonance
- Very small size alone
- Presence of a nonbonding lone pair only
Correct Answer: Ability to stabilize positive charge via hyperconjugation or resonance
Q34. Which is the correct sequence of mechanistic events in the ketone Schmidt rearrangement?
- Carbonyl protonation → azide attack → rearrangement and N2 loss → nitrilium formation → hydrolysis to amide
- Radical initiation → hydrogen abstraction → radical recombination → amide formation
- Base-catalyzed enolate formation → elimination → amide formation
- Direct nucleophilic substitution at oxygen → ether formation
Correct Answer: Carbonyl protonation → azide attack → rearrangement and N2 loss → nitrilium formation → hydrolysis to amide
Q35. Which reaction condition tends to favor migration of an aryl group over an alkyl group in Schmidt rearrangement?
- When aryl migration provides resonance stabilization of the developing positive charge
- Low temperature only
- Presence of excess base
- Strong reducing conditions
Correct Answer: When aryl migration provides resonance stabilization of the developing positive charge
Q36. Which byproduct needs to be carefully vented during the Schmidt rearrangement?
- Nitrogen gas evolved during decomposition of azide
- Methane gas as a toxic byproduct
- Hydrogen chloride gas in all cases
- Chlorine gas from acid
Correct Answer: Nitrogen gas evolved during decomposition of azide
Q37. Which substrate class is most directly converted to primary amines via Schmidt-type decarboxylative amination?
- Carboxylic acids treated with hydrazoic acid under acidic conditions
- Alkenes under hydroboration conditions
- Aromatic nitro compounds under hydrogenation
- Alcohols under dehydration conditions
Correct Answer: Carboxylic acids treated with hydrazoic acid under acidic conditions
Q38. Which of the following is true about intramolecular Schmidt reactions?
- They are powerful for constructing nitrogen-containing ring systems and can give ring expansion
- They always produce open-chain amines only
- They cannot be used to synthesize lactams
- They are free-radical cyclizations requiring peroxides
Correct Answer: They are powerful for constructing nitrogen-containing ring systems and can give ring expansion
Q39. Which structural evidence in NMR would support formation of an amide after Schmidt rearrangement?
- Downfield NH proton signals (if present) and carbonyl carbon around 165–175 ppm in 13C NMR
- Absence of any carbonyl carbon signal
- Sharp singlet at 0 ppm only
- Large upfield shifts for all protons
Correct Answer: Downfield NH proton signals (if present) and carbonyl carbon around 165–175 ppm in 13C NMR
Q40. Which precaution is important when disposing of azide-containing waste from Schmidt reactions?
- Avoid concentration and contact with heavy metals; quench under controlled conditions to benign products
- Evaporate to dryness and discard solids in sink
- Mix with strong oxidizer before disposal
- Burn azide waste in open air
Correct Answer: Avoid concentration and contact with heavy metals; quench under controlled conditions to benign products
Q41. Which statement distinguishes Schmidt rearrangement from Beckmann rearrangement?
- Schmidt uses azide chemistry to form amides/amines; Beckmann involves oxime conversion to amides under acid
- Both reactions use oximes and are identical
- Beckmann always uses hydrazoic acid
- Schmidt is a photochemical reaction only
Correct Answer: Schmidt uses azide chemistry to form amides/amines; Beckmann involves oxime conversion to amides under acid
Q42. Which industrially important lactam can be accessed by ring-expansion strategies related to the Schmidt reaction?
- Caprolactam (precursor to Nylon-6)
- γ-Butyrolactone only
- Acetone
- Benzene
Correct Answer: Caprolactam (precursor to Nylon-6)
Q43. Which parameter is least likely to directly change the product distribution in a Schmidt rearrangement?
- Ambient light intensity with no photochemical pathway
- Acid strength and type
- Substrate substitution and migratory aptitude
- Presence of water for hydrolysis
Correct Answer: Ambient light intensity with no photochemical pathway
Q44. Which observation indicates that an intramolecular Schmidt rearrangement has occurred successfully on a cyclic ketone?
- Formation of a larger ring lactam confirmed by MS and IR
- Complete recovery of starting ketone only
- Immediate precipitation of metallic salts
- Formation of a diol product exclusively
Correct Answer: Formation of a larger ring lactam confirmed by MS and IR
Q45. Which of the following best explains why tertiary alkyl groups often migrate more readily than primary in Schmidt rearrangement?
- Tertiary groups better stabilize positive charge in the transition state by hyperconjugation
- Tertiary groups are smaller and more mobile
- Primary groups form more stable carbocations
- Tertiary groups always form radicals first
Correct Answer: Tertiary groups better stabilize positive charge in the transition state by hyperconjugation
Q46. Which synthetic step commonly follows the formation of an isocyanate from acyl azide in Curtius/related pathways to give an amine?
- Hydrolysis or reaction with nucleophile to give a primary amine or carbamate
- Oxidation to a carboxylic acid
- Dehydration to an alkene
- Direct methylation to form tertiary amine
Correct Answer: Hydrolysis or reaction with nucleophile to give a primary amine or carbamate
Q47. Which approach can be used to favor formation of a particular migration product in a substrate with two competitive migrating groups?
- Modify electronic properties or steric environment to favor one group’s ability to stabilize the developing positive charge
- Change the color of reaction vessel
- Use nonreactive gas bubbling to stir the mixture
- Always add radical initiator
Correct Answer: Modify electronic properties or steric environment to favor one group’s ability to stabilize the developing positive charge
Q48. Which mechanistic probe would help confirm a nitrilium intermediate in the Schmidt rearrangement?
- Trapping experiments with water or alcohols to give amide or imidate derivatives
- Measuring conductivity of the solution only
- Observing color change to red only
- Adding peroxide to see explosive decomposition
Correct Answer: Trapping experiments with water or alcohols to give amide or imidate derivatives
Q49. Which is an environmentally and operationally greener alternative in performing Schmidt-type chemistry?
- Use of safer azide sources, microflow reactors, and in situ generation with careful venting to minimize azide handling
- Using neat HN3 at high concentration for speed
- Combining azides with heavy metal salts to speed reaction
- Carrying out reaction without ventilation to conserve energy
Correct Answer: Use of safer azide sources, microflow reactors, and in situ generation with careful venting to minimize azide handling
Q50. Which best practice should B. Pharm students remember when studying Schmidt rearrangement for examinations and lab work?
- Understand mechanism, migratory aptitude, synthetic applications, hazards of azides, and analytical confirmation of products
- Only memorize reagent names without mechanism
- Assume Schmidt reaction always gives the same product regardless of substrate
- Ignore safety since azides are harmless in small amounts
Correct Answer: Understand mechanism, migratory aptitude, synthetic applications, hazards of azides, and analytical confirmation of products
