Alkynes extend alkene chemistry while adding new features: higher unsaturation, linear geometry, acidic terminal hydrogens, and distinctive partial-reduction pathways.
Prepare alkynes by double elimination and identify conditions that generate terminal versus internal alkynes.
Use strong base to form acetylide anions and apply them in carbon-carbon bond formation.
Predict full and partial reductions of alkynes with correct alkene stereochemistry.
Apply hydration, halogenation, and hydroboration chemistry to terminal and internal alkynes.
Checkpoint Questions
Q: What happens when 1-butyne is treated with NaNH2 and then CH3I?
A: The terminal alkyne is deprotonated to an acetylide, which alkylates CH3I to give 2-pentyne.
Q: How can you stop reduction of an alkyne at the cis alkene stage?
A: Use a poisoned catalyst such as Lindlar catalyst.