Organic Lecture 2/19

Review

• Cycloheptatriene: one that’s aromatic is the cation because of 4n+2 electrons, satisfying Huckel’s rules.

• Heterocycles can be aromatic as well: can re-hybridize to make aromatic.

• Making benzene ring: 3 acetylenes, Cu or Fe, and heat

Reaction of Arenes

• Generally unreactive, but if they do react it will happen via substitution. Require harsh conditions because of how stable an arene is.

• Birch reduction: convert benzene into non-conjugated diene. Uses Na, NH3 and CH3OH.

Mechanism of Birch Reduction

-always forms more stable alkene, more substituted

Oxidized Arenes:

• Usually resistant to oxidation because nothing can be pulled off. Much rather go through combustion.

• Side Chain Oxidation: needs at least one benzylic hydrogen

Electrophilic Aromatic Substitutions (EAS):

• The electrophile has to be ridiculously unstable for the pi bond on aromatic to come grab it.

• Mechanism: generate electrophile (fast), form carbocation(slow), then regeneration of aromaticity(fast)

• Electrophiles to use: Cl+, NO2+, C+(CH3)3, and SO3

Halogenation of Arenes: