Page 41 - Mechanism and Theory in Organic Chemistry

Bas~s orbitals
Molecular orbitals
- Antibonding
1 Bonding
Figure 1.19 The n- MO's for butadiene.
The reader will also be aware that not all cyclic conjugated molecules for
which such equivalent structures may be written share with benzene these
special properties. For example, cyclobutadiene (28) eluded synthesis for many
years; when finally prepared, it and its simple derivatives proved to be extremely

28
reactive and capable of existence only when immobilized by freezing in an inert