14. AROMATIC COMPOUNDS. (approx. lecture time: 2 lectures)Topics covered: 14.1-14.7A,14.7D,14.8A,14.9.

Benzenemore than just cyclic conjugation: aromatic stabilization

Some Simple Benzene Derivatives

The Halifax Explosion of 1917The Halifax Explosion occurred on Thursday, December 6, 1917, when the city was devastated by the huge detonation of the SS Mont-Blanc, a French cargo ship fully loaded with wartime explosives, which accidentally collided with the Norwegian ship the SS Imo in "The Narrows" section of Halifax Harbour. About 2,000 people were killed and over 9,000 people were injured. The Halifax Explosion remains the World’s largest accidental explosion.

Picric AcidTNT; 2,4,6-trinitrotoluene

If you are from Nova Scotia, you will definitely know about it!

O2N NO2

NO2

CH3 OHNO2O2N

NO2

The Phenomenon of Aromatic Stabilization

Molecular Orbital Picture of the p Bonding in Benzene

Mnemonic for Generating Molecular Orbital Energy Levels for Benzene

Joining benzene rings to each other will always create an aromatic system!

“mothballs”

potent carcinogen

Hückel’s 4n + 2 p Electron Rule

Hückel’s rule is concerned with compounds containing one planar ring in which each atom has a pz orbital as in benzene.

“Planar monocyclic rings containing 4n + 2 p electrons, where n = 0, 1, 2, 3, and so on (i.e., rings containing 2, 6, 10, 14 . .p electrons) should be aromatic, i.e., show exceptional stability relative to similar systems without this electron count”

Examples of Hückel’s 4n + 2 p Electron Rule

Cyclooctatetraene

Imidazole

Imidazole is an aromatic compound that is important in biological systems. The two nitrogens are not equivalent! Learn how to tell them apart.

The DNA Bases are Aromatic Compounds

Sunscreens and Sunblocks(Organic chemists can become wealthy without making drugs)

Sunblocks: just “blocks” the sun’s rays. Use TiO2 and ZnO2. But will look geeky.

Sunscreens: organic compounds that converts the UV light into thermal energy. These are “designer compounds” so we can charge much more than inorganics. They also have many industrial uses!

PABA

Oxybenzone

Avobenzone

4-MBC

Tinosorb M

OOH

OCH3

O O

CH3O

OCH3

CO2H

NH2

NN

N

N

N

N

OH OH