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.
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.
•Resonance: conjugated,
delocalized pi electrons lead
to resonance structures:
Historical Representations of Benzene
•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.
NH
Lone electron pair can
count towards aromaticity
•Why are these compounds non-aromatic?
Aromatic Ions