Named Reactions: Ullmann coupling reactions MCQs With Answer

Introduction: Named reactions are cornerstones of advanced organic synthesis, and the Ullmann coupling family plays a vital role in constructing C–C, C–O and C–N bonds in pharmaceutical chemistry. This quiz collection focuses on Ullmann and Ullmann-type reactions, covering mechanistic concepts, catalysts, ligands, substrate scope, limitations and modern improvements that make these reactions relevant for M.Pharm students. Questions probe classical high‑temperature processes and contemporary ligand‑enabled, low‑temperature methods, emphasizing practical considerations such as choice of halide, bases, solvents and monitoring techniques. Working through these MCQs will strengthen understanding of when and how to apply Ullmann chemistry in medicinal and process chemistry contexts.

Q1. What is the primary bond-forming outcome of a classical Ullmann coupling between two aryl halides?

• Formation of a biaryl (C–C) bond
• Formation of an ether (C–O) bond
• Formation of an amide (C–N) bond
• Formation of an alkene (C=C) bond

Correct Answer: Formation of a biaryl (C–C) bond

Q2. Which metal is central to the traditional Ullmann coupling reaction?

• Copper
• Palladium
• Nickel
• Ruthenium

Correct Answer: Copper

Q3. Historically, what was a defining experimental requirement for classical Ullmann couplings?

• High temperature (often >150 °C)
• Low temperature (below 0 °C)
• Room temperature conditions
• Photochemical activation only

Correct Answer: High temperature (often >150 °C)

Q4. For reactivity in Ullmann couplings of aryl halides, which halide is generally most reactive?

• Aryl iodides are most reactive
• Aryl chlorides are most reactive
• Aryl bromides are most reactive
• All halides show equal reactivity

Correct Answer: Aryl iodides are most reactive

Q5. Which type of ligand has been widely used to accelerate and lower the temperature of Ullmann couplings?

• N,N‑diamines such as N,N‑dimethylethylenediamine (DMEDA)
• Triphenylphosphine
• N‑heterocyclic carbenes (NHCs) exclusively
• No ligand works for Ullmann reactions

Correct Answer: N,N‑diamines such as N,N‑dimethylethylenediamine (DMEDA)

Q6. Which mechanistic step in Ullmann-type couplings remains a subject of debate in the literature?

• Whether oxidative addition of an aryl halide to Cu(I) to form Cu(III) occurs
• Formation of carbonyl intermediates
• Involvement of a palladium co-catalyst in every case
• Direct nucleophilic aromatic substitution without metal

Correct Answer: Whether oxidative addition of an aryl halide to Cu(I) to form Cu(III) occurs

Q7. The Ullmann–Goldberg reaction specifically refers to which transformation?

• N‑Arylation to form aryl amines (C–N bond formation)
• O‑Arylation to form diaryl ethers (C–O bond formation)
• C–C homocoupling of alkenes
• Formation of alkyl halides from alcohols

Correct Answer: N‑Arylation to form aryl amines (C–N bond formation)

Q8. Which base is commonly employed in many Ullmann coupling protocols?

• Potassium carbonate (K2CO3)
• Hydrochloric acid (HCl)
• Sodium chloride (NaCl)
• Phenol

Correct Answer: Potassium carbonate (K2CO3)

Q9. How do strong electron-withdrawing substituents on the aryl halide typically affect Ullmann coupling rates?

• They accelerate the reaction
• They completely stop the reaction
• They have no effect
• They always reverse selectivity

Correct Answer: They accelerate the reaction

Q10. Intramolecular Ullmann couplings are especially useful for the synthesis of which structural motif?

• Biaryl rings leading to polycyclic or fused aromatic systems
• Simple aliphatic alcohols
• Symmetric alkanes
• Terminal alkynes

Correct Answer: Biaryl rings leading to polycyclic or fused aromatic systems

Q11. Which solvent is commonly used in Ullmann-type reactions due to its high polarity and ability to dissolve salts?

• Dimethylformamide (DMF)
• Hexane
• Diethyl ether
• Carbon tetrachloride

Correct Answer: Dimethylformamide (DMF)

Q12. Which modern catalyst form has been applied to lower reaction temperatures and improve activity in Ullmann couplings?

• Copper nanoparticles
• Bulk metallic silver
• Gold foils
• Mercury amalgam

Correct Answer: Copper nanoparticles

Q13. What is a historically significant limitation of classical Ullmann couplings that has prompted ligand development?

• Poor reactivity of aryl chlorides under unmodified conditions
• Inability to form C–C bonds
• Exclusive formation of polymers
• Complete lack of regioselectivity with monosubstituted arenes

Correct Answer: Poor reactivity of aryl chlorides under unmodified conditions

Q14. Which organocopper intermediate is commonly invoked in Ullmann reaction mechanisms?

• Aryl–Cu(I) species (arylcopper(I))
• Aryl–Pd(II) hydride
• Aryl–MgBr Grignard complex
• Aryl radical cation exclusively

Correct Answer: Aryl–Cu(I) species (arylcopper(I))

Q15. The coupling of an aryl halide with a phenol under Ullmann conditions to give diaryl ethers is known as:

• Ullmann ether synthesis
• Sandmeyer reaction
• Suzuki coupling
• Wittig reaction

Correct Answer: Ullmann ether synthesis

Q16. Which ligand class stabilizes copper intermediates and is widely credited with expanding substrate scope for Ullmann reactions?

• Diamine ligands
• Tertiary sulfides
• Carboxylic acids
• Aliphatic alcohols

Correct Answer: Diamine ligands

Q17. For milder Pd‑catalyzed alternatives to Ullmann N‑ and O‑arylation, which named methodology is most relevant?

• Buchwald–Hartwig amination
• Knoevenagel condensation
• Claisen rearrangement
• Wacker oxidation

Correct Answer: Buchwald–Hartwig amination

Q18. To favor a cross‑coupling product over homocoupling in Ullmann chemistry, which strategy is commonly used?

• Use an aryl halide and a distinct nucleophilic coupling partner (e.g., phenol or amine)
• Use two identical aryl halides in equal amounts
• Exclude any base from the reaction
• Perform the reaction under photochemical conditions only

Correct Answer: Use an aryl halide and a distinct nucleophilic coupling partner (e.g., phenol or amine)

Q19. Which analytical technique is especially useful for identifying and confirming formation of small-molecule biaryl products from Ullmann couplings?

• Gas chromatography–mass spectrometry (GC–MS)
• Polarimetry
• Flame photometry
• Paper chromatography only

Correct Answer: Gas chromatography–mass spectrometry (GC–MS)

Q20. What is a major advantage of modern ligand‑assisted Ullmann protocols compared with classical conditions?

• Lower reaction temperature and broader substrate scope
• They require larger excesses of metal powder
• They always require cryogenic conditions
• They eliminate the need for any base

Correct Answer: Lower reaction temperature and broader substrate scope

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