Alkynes

Question 1

How can you reduce an alkyne to form a trans-alkene

Answer 1

1. Sodium metal in liquid ammonia

2. Dissolving metal reduction

Question 2

How can you reduce an alkyne to form a cis-alkene

Answer 2

1. Selective hydrogenation over Lindlar’s catalyst
2. A palladium catalyst which has been deliberately poisoned with lead and quinolines to stop it catalysis over-reduction to an alkane

Question 3

Why are alkynes easy to introduce to reactions

Answer 3

1. The proton on the end of terminal alkyne is acidic enough that strong bases can abstract it giving an acetylide anion.
2. This anion is nucleophilic and will add to carbonyls as well as displacing leaving groups in nucleophilic substitution reactions.

Question 4

Which functional groups often need protecting groups

Answer 4

1. COOH
2. OH
3. NH

Question 5

Give an example of a strong base that can be used to deprotonate an alkyne

Answer 5

1. NaNH2