1. CH 14-2 Characteristics of Benzene
Hydrogen deficiency
All carbons in ring are sp2 hybridized
Geometry
Reactivity of benzene vs alkenes
Benzene is ONE example of a class of compounds characterized as “AROMATIC.” These compounds possess the physical property of “AROMATICITY.”
AROMATICITY is a physical property that explains the unique stability, reactions and toxicity of benzene and related compounds.

2. Aromaticity Conjugation: each atom of the ring has a p-orbital.
Delocalization: since the p-orbitals are all conjugated, the pi electrons can move freely from one orbital to the next; the pi electrons are delocalized.

3. Resonance: conjugated, delocalized pi electrons lead to resonance structures:

4. Historical Representations of Benzene

5. How can we tell if a compound is aromatic?
Huckel’s Rule: Aromaticity exists if # pi electrons = 4n + 2
Since n = any whole #, there are Huckle #’s of pi electrons for aromatic compounds (n = 0, 1, 2, 3: 2, 6, 10, 14, etc.
Lone electron pair can count towards aromaticity
Why are these compounds non-aromatic?

6. Aromatic Ions