Adrian Mulholland

Molecular Structure and Bonding

p electrons in conjugated organic molecules

Lecture 3

• Aromaticity and stability

· Comparing Hückel Theory with experiments

• p-electron charge and p-electron bond order

Aromaticity

• The Circle Method leads to an important result of Hückel Theory, the prediction of the stability of ‘aromatic’ molecules.

• Planar cyclic conjugated hydrocarbons with (4n +2) p –electrons are predicted to be highly stable: they have a closed shell electronic configuration (no unpaired electrons, and no partly filled MO energy levels).

• They also have high delocalization energies. The classic example is benzene.

Next: comparing with experiments