Decarboxylation MCQs With Answer

Decarboxylation MCQs With Answer is an essential resource for B. Pharm students studying drug chemistry, metabolism, and formulation stability. This concise introduction covers core concepts such as thermal, enzymatic and catalytic decarboxylation, reaction mechanisms, cofactors, and pharmaceutical implications like prodrug activation and degradation pathways. Emphasis is placed on analytical detection methods (GC-MS, TGA, DSC), common named reactions (Kolbe, Hunsdiecker, Barton), and factors affecting reaction rate including temperature, solvent, and catalysts. Clear, targeted practice helps strengthen understanding of both organic reaction theory and practical pharmaceutical applications. ‘Now let’s test your knowledge with 50 MCQs on this topic.’

Q1. What is decarboxylation in the context of organic chemistry?

• The addition of a carboxyl group to a molecule
• The removal of a carboxyl group as carbon dioxide
• The oxidation of a hydroxyl group to a carbonyl
• The formation of an ester from an acid and alcohol

Correct Answer: The removal of a carboxyl group as carbon dioxide

Q2. Which cofactor is commonly required by pyruvate decarboxylase enzymes in biological decarboxylation?

• NADH
• Thiamine pyrophosphate (TPP)
• Flavin adenine dinucleotide (FAD)
• Biotin

Correct Answer: Thiamine pyrophosphate (TPP)

Q3. Which named reaction involves electrochemical decarboxylation to form radical intermediates and coupling products?

• Hunsdiecker reaction
• Barton decarboxylation
• Kolbe electrolysis
• Kolbe-Schmitt reaction

Correct Answer: Kolbe electrolysis

Q4. The Hunsdiecker reaction transforms carboxylic acids into which type of product?

• Alkyl halides via decarboxylative halogenation
• Alcohols via reduction
• Esters via transesterification
• Amines via amide formation

Correct Answer: Alkyl halides via decarboxylative halogenation

Q5. Which analytical technique is best suited to monitor mass loss during thermal decarboxylation?

• Infrared spectroscopy (IR)
• Thermogravimetric analysis (TGA)
• Ultraviolet-visible spectroscopy (UV-Vis)
• High-performance liquid chromatography (HPLC)

Correct Answer: Thermogravimetric analysis (TGA)

Q6. In pharmaceutical formulation, unwanted decarboxylation most directly affects:

• Solubility but not potency
• Color only
• Drug potency and chemical stability
• Packaging size

Correct Answer: Drug potency and chemical stability

Q7. Which reagent is commonly used for radical decarboxylation in organic synthesis known as Barton decarboxylation?

• Lead tetraacetate
• Nitrogen dioxide
• Thionyl chloride
• Thiol and radical initiator (e.g., Barton ester + Bu3SnH)

Correct Answer: Thiol and radical initiator (e.g., Barton ester + Bu3SnH)

Q8. Oxidative decarboxylation in metabolic pathways typically converts:

• Fatty acids into amino acids
• Alpha-keto acids into CO2 and acyl products
• Alcohols into esters
• Alkenes into epoxides

Correct Answer: Alpha-keto acids into CO2 and acyl products

Q9. Which of the following best describes Kolbe decarboxylative coupling?

• Formation of alkenes from carboxylic acids and aldehydes
• Electrochemical generation of radicals from carboxylates leading to C–C coupling
• Decarboxylative formation of nitriles
• Acylation of aromatic rings using carboxylic acids

Correct Answer: Electrochemical generation of radicals from carboxylates leading to C–C coupling

Q10. In a decarboxylation reaction, which factor most commonly increases the reaction rate?

• Decreasing temperature
• Increasing steric hindrance at the reaction site
• Using a catalyst or higher temperature
• Removing solvent entirely

Correct Answer: Using a catalyst or higher temperature

Q11. Which cofactor is essential for aromatic L-amino acid decarboxylase activity?

• Biotin
• Pyridoxal phosphate (PLP)
• Vitamin C
• Coenzyme A

Correct Answer: Pyridoxal phosphate (PLP)

Q12. Thermal decarboxylation of aromatic carboxylic acids typically requires:

• Lower temperatures than aliphatic acids
• High temperatures or catalysts due to aromatic stabilization
• No activation energy
• Only enzymatic conditions

Correct Answer: High temperatures or catalysts due to aromatic stabilization

Q13. Which product results from decarboxylation of acetoacetic acid?

• Acetone
• Acetic acid
• Carbon monoxide
• Malonic acid

Correct Answer: Acetone

Q14. Decarboxylative cross-coupling reactions are valuable in drug synthesis because they:

• Introduce oxygen into molecules
• Allow formation of C–C bonds from abundant carboxylic acids
• Create peptides directly
• Reduce the need for protecting groups in all cases

Correct Answer: Allow formation of C–C bonds from abundant carboxylic acids

Q15. Which gas is directly released during a decarboxylation reaction?

• Methane
• Nitrogen
• Carbon dioxide
• Hydrogen chloride

Correct Answer: Carbon dioxide

Q16. In prodrug design, decarboxylation can be used to:

• Make drugs permanently inactive
• Activate a prodrug to its active form in vivo
• Increase molecular weight intentionally
• Prevent absorption in the gut

Correct Answer: Activate a prodrug to its active form in vivo

Q17. Which named reaction uses silver salts and leads to decarboxylative halogenation?

• Hunsdiecker reaction
• Barton-McCombie reaction
• Knoevenagel condensation
• Buchwald-Hartwig coupling

Correct Answer: Hunsdiecker reaction

Q18. Decarboxylation of beta-keto acids is typically:

• Slow and endothermic
• Fast and spontaneous due to stabilization of enolate intermediate
• Impossible without a metal catalyst
• Only observed under enzymatic conditions

Correct Answer: Fast and spontaneous due to stabilization of enolate intermediate

Q19. Which instrument combination is ideal to identify decarboxylation products in complex mixtures?

• IR alone
• GC-MS and NMR
• Paper chromatography
• Simple melting point

Correct Answer: GC-MS and NMR

Q20. Which statement about decarboxylation in the citric acid cycle is true?

• There are no decarboxylation steps in the citric acid cycle
• Decarboxylation steps generate CO2 and reduce cofactors like NAD+
• Decarboxylation steps generate CO2 and reduce NAD+ to NADH
• Decarboxylation steps always produce ATP directly

Correct Answer: Decarboxylation steps generate CO2 and reduce NAD+ to NADH

Q21. Which type of decarboxylation is typically catalyzed by decarboxylase enzymes using PLP?

• Alpha and beta carboxyl removal from amino acids
• Direct reduction of carboxyl to alcohol
• Oxidative cleavage of ethers
• Electrochemical coupling

Correct Answer: Alpha and beta carboxyl removal from amino acids

Q22. Which factor least affects the rate of chemical decarboxylation?

• Electronic stabilization of the carbanion intermediate
• Temperature
• Solvent polarity
• The color of the reaction vessel

Correct Answer: The color of the reaction vessel

Q23. Malonic ester synthesis relies on decarboxylation to:

• Generate an enolate that can alkylate
• Remove halogens from substrates
• Introduce amino groups
• Saponify esters directly

Correct Answer: Generate an enolate that can alkylate

Q24. Which is a common catalyst used in modern decarboxylative cross-coupling?

• Palladium or nickel complexes
• Gold nanoparticles exclusively
• Sodium chloride
• Pure oxygen gas

Correct Answer: Palladium or nickel complexes

Q25. Decarboxylation of salicylic acid to form phenol under harsh conditions is an example of:

• Decarboxylation of an aromatic acid
• Decarboxylative amination
• Reduction to an alcohol
• Oxidative cleavage

Correct Answer: Decarboxylation of an aromatic acid

Q26. Which decarboxylation mechanism involves formation of a resonance-stabilized carbanion followed by loss of CO2?

• Radical decarboxylation
• Pericyclic decarboxylation
• Concerted decarboxylation via stabilized anion (e.g., beta-keto acids)
• Electrophilic aromatic substitution

Correct Answer: Concerted decarboxylation via stabilized anion (e.g., beta-keto acids)

Q27. In drug metabolism, nonenzymatic decarboxylation is most likely to occur under:

• Cold, acidic storage
• High temperature or extreme pH
• Complete darkness only
• Neutral aqueous conditions at 4°C

Correct Answer: High temperature or extreme pH

Q28. Which experimental evidence indicates decarboxylation has occurred?

• Increase in molecular weight of analyte
• Detection of CO2 evolution and disappearance of carboxyl signal in NMR
• No change in IR signals
• Only a color change with no spectroscopic change

Correct Answer: Detection of CO2 evolution and disappearance of carboxyl signal in NMR

Q29. Which of the following decarboxylation pathways is commonly mediated by peroxidases or oxidases?

• Nonoxidative decarboxylation of beta-keto acids
• Oxidative decarboxylation of aromatic acids forming quinones
• Electrochemical Kolbe coupling
• Photochemical hydrolysis

Correct Answer: Oxidative decarboxylation of aromatic acids forming quinones

Q30. The stability of a drug with a carboxylic acid group can be improved by:

• Leaving it exposed to high heat
• Converting it to an ester prodrug or salt
• Adding free radical initiators
• Storing in strong base indefinitely

Correct Answer: Converting it to an ester prodrug or salt

Q31. Which method is often used to induce decarboxylation of cannabinoids in formulation science?

• Cold shock
• Thermal heating under controlled conditions
• Adding acid to neutral pH
• Exposing to oxygen-free environment only

Correct Answer: Thermal heating under controlled conditions

Q32. Which type of decarboxylation yields an alkene from a carboxylic acid derivative via elimination?

• Decarboxylative dehydration
• Decarboxylative hydrogenation
• Decarboxylative amination
• Decarboxylative halogenation

Correct Answer: Decarboxylative dehydration

Q33. In radical decarboxylation, which species commonly initiates the process?

• Carbanion generated by strong base
• Radical initiator or single-electron transfer (SET) event
• Proton donor only
• Molecular oxygen without catalyst

Correct Answer: Radical initiator or single-electron transfer (SET) event

Q34. Which of the following is TRUE about Kolbe electrolysis products?

• They always form heteroatomic bonds
• They typically form symmetric hydrocarbons by radical coupling
• They only produce alcohols
• They require enzymatic catalysis

Correct Answer: They typically form symmetric hydrocarbons by radical coupling

Q35. Which observation suggests enzymatic decarboxylation rather than thermal decarboxylation?

• Reaction proceeds best at 90–200°C
• Reaction is stereospecific and occurs at physiological temperature
• Large amounts of CO2 at room temperature without selectivity
• Requires strong mineral acid

Correct Answer: Reaction is stereospecific and occurs at physiological temperature

Q36. The loss of which NMR signal would most directly indicate decarboxylation of an organic acid?

• Disappearance of the CH3 singlet
• Disappearance of the carboxyl carbon (13C ~170–180 ppm)
• Disappearance of aromatic protons only
• Appearance of a new OH peak

Correct Answer: Disappearance of the carboxyl carbon (13C ~170–180 ppm)

Q37. Which decarboxylation is commonly used to generate alkenes from alpha,beta-unsaturated acids?

• Pericyclic thermal decarboxylation
• Kolbe electrolysis only
• Hydrogenolysis
• Ozonolysis

Correct Answer: Pericyclic thermal decarboxylation

Q38. In organic synthesis, decarboxylative borylation converts carboxylic acids into:

• Boronic esters useful for cross-coupling
• Carboxylate salts only
• Nitro compounds
• Amides exclusively

Correct Answer: Boronic esters useful for cross-coupling

Q39. Which of the following best explains why beta-keto acids decarboxylate readily?

• Loss of CO2 forms a stabilized enolate or resonance-stabilized anion
• They have no resonance stabilization
• Decarboxylation of beta-keto acids is always endothermic
• They require metal catalysts exclusively

Correct Answer: Loss of CO2 forms a stabilized enolate or resonance-stabilized anion

Q40. Which laboratory safety consideration is important when performing thermal decarboxylation?

• Ensure proper ventilation to remove evolved CO2 and volatile by-products
• No special precautions are necessary
• Seal the system completely without venting
• Only wear eye protection; no ventilation needed

Correct Answer: Ensure proper ventilation to remove evolved CO2 and volatile by-products

Q41. Photochemical decarboxylation typically proceeds via:

• Direct thermal cleavage without light
• Excited-state single-electron transfer producing radicals
• Base-catalyzed anion formation only
• Acid-catalyzed esterification

Correct Answer: Excited-state single-electron transfer producing radicals

Q42. In the Hunsdiecker reaction, which halogen source is commonly involved?

• Hydrogen fluoride
• Bromine with silver carboxylate
• Sodium iodide alone
• Chlorine gas without metal salts

Correct Answer: Bromine with silver carboxylate

Q43. Which type of decarboxylation is most commonly reversible under mild conditions?

• Thermal decarboxylation of aromatic acids
• Enzymatic decarboxylation in metabolic pathways is typically irreversible
• Decarboxylation of beta-keto acids is easily reversible
• Carboxylation/decarboxylation equilibria with CO2 under controlled conditions

Correct Answer: Carboxylation/decarboxylation equilibria with CO2 under controlled conditions

Q44. Which is a pharmaceutical example where decarboxylation is part of metabolism?

• Conversion of aspirin to salicylic acid only
• Decarboxylation of L-DOPA by aromatic L-amino acid decarboxylase to form dopamine
• Hydrolysis of esters to alcohols
• Direct glucuronidation without bond cleavage

Correct Answer: Decarboxylation of L-DOPA by aromatic L-amino acid decarboxylase to form dopamine

Q45. Which solvent property often accelerates ionic decarboxylation mechanisms?

• Low dielectric constant
• High polarity and ability to stabilize charge
• Complete absence of hydrogen bonding
• Very nonpolar, aprotic nature only

Correct Answer: High polarity and ability to stabilize charge

Q46. Which research technique helps determine the activation energy for decarboxylation?

• Thin-layer chromatography
• Arrhenius analysis using rate data from different temperatures
• Simple pH paper test
• Visual inspection of color change

Correct Answer: Arrhenius analysis using rate data from different temperatures

Q47. Which decarboxylation strategy is often used to avoid harsh thermal conditions in synthesis?

• Using radical initiators or photoredox catalysis for milder conditions
• Increasing reaction temperature to extreme levels
• Adding large amounts of strong acid
• Skipping purification steps

Correct Answer: Using radical initiators or photoredox catalysis for milder conditions

Q48. Which structural feature makes a carboxylic acid more prone to decarboxylation?

• Lack of adjacent electron-withdrawing groups
• Presence of adjacent electron-withdrawing or resonance-stabilizing groups
• Bulky tertiary substituents only
• High saturation with no conjugation

Correct Answer: Presence of adjacent electron-withdrawing or resonance-stabilizing groups

Q49. Which of the following is a disadvantage of decarboxylative reactions in pharmaceutical manufacturing?

• They always improve yield
• Formation of unwanted volatile by-products and CO2 management issues
• They require no optimization
• They never require catalysts

Correct Answer: Formation of unwanted volatile by-products and CO2 management issues

Q50. Which safety and regulatory consideration is important when scaling decarboxylation processes pharmaceutically?

• Ignoring gas handling requirements is acceptable
• Proper management of evolved gases, waste streams, and solvent emissions
• No need for process hazard analysis
• Only aesthetics of production area matter

Correct Answer: Proper management of evolved gases, waste streams, and solvent emissions

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.

Mail- Sachin@pharmacyfreak.com