MChem Master of Chemistry Master of Chemistry: Organic Chemistry 4

Question 1

Which reaction mechanism is responsible for the polymerization of ethylene using a Ziegler-Natta catalyst?

Accepted Answer

Anionic coordination-insertion polymerization

Answer

Ziegler-Natta catalysts operate via a coordination-insertion mechanism in which the alkene coordinates to the transition metal and inserts into the metal–carbon bond.

Question 2

What does the term 'retrosynthetic analysis' mean in organic synthesis?

Accepted Answer

Systematically deconstructing a target molecule into simpler precursors by breaking strategic bonds

Answer

Retrosynthetic analysis (Corey's disconnection approach) works backward from the target molecule, identifying bond disconnections that map to known forward reactions.

Question 3

Which of the following substituents is meta-directing in electrophilic aromatic substitution?

Accepted Answer

–NO2

Answer

Electron-withdrawing groups such as –NO2 destabilize the carbocation intermediate at ortho/para positions more than at meta, making meta the preferred site of attack.

Question 4

In the aldol condensation, what type of intermediate is initially formed before dehydration?

Accepted Answer

A β-hydroxy carbonyl compound

Answer

The aldol addition step produces a β-hydroxy carbonyl compound; subsequent base- or acid-catalyzed dehydration gives the α,β-unsaturated carbonyl product.

Question 5

How does the Wittig reaction construct a carbon–carbon double bond?

Accepted Answer

Through a betaine/oxaphosphetane intermediate that decomposes to give an alkene and Ph3P=O

Answer

The phosphorus ylide reacts with the carbonyl to form a four-membered oxaphosphetane ring, which undergoes retrocycloaddition to give the alkene and triphenylphosphine oxide.

MChem Master of Chemistry Practice Test

MChem Master of Chemistry Practice Test

MChem Master of Chemistry Master of Chemistry: Organic Chemistry 4