Chapter 9: Alkynes

Terminal Alkyne

The triple bond has an H attached at one end and is characterized by the general formula R-C#C-H, where R represents a hydrocarbon group.

This is acidic because the conjugate base is more stable

Internal alkyne

The triple bond connects two carbon atoms, both of which are part of hydrocarbon groups, making it less acidic compared to terminal alkynes.

Bases used to deproponate terminal alkynes

Sodium Amide (NH2)

n-butyl lithium

Sodium hydride

Germinal dihalide

This means two halogens are on the same carbon

Vicinal dihalide

This means halogens are on the adjacent carbons

Complete reduction: Catalytic Hydrogenation

We are converting alkynes to alkanes.

Reagents: H2 /. pt/ni

Partial hydrogenation

We are converting an alkyne to an alkene. Cis Configuration

Reagents: H2/Lindlar’s catalyst, quinoline, pd/baso4, MeOH

Dissolving metal reduction

Reduces an alkyne to a trans alkene with sodium metal and ammonia

Hydration of Alkynes

Adding H and OH

• follows markonikovs’s rule

• generates a ketone

• reagents: H2SO4, H20/ HgSO4

Enol

Alkene and alcohol, not stable so it undergoes tautomerization.

Tautomerization

The process where a molecule interconverts between two distinct isomers called tautomers

Tautomers

Constitutional isomers that rapidly interconvert via migration of a proton