[3] In the mid 19th century, investigators proposed several possible structures for benzene which were consistent with its empirical formula, C6H6, which had been determined by combustion analysis.

The first, which was proposed by Friedrich August Kekulé von Stradonitz in 1865, later proved to be closest to the true structure of benzene.

The deviation of the carbon-carbon bond angle from 109° to 60° in a triangle leads to a high ring strain, reminiscent of that of cyclopropane but greater.

Due to this ring strain, the bonds have a low bond energy and break at a low activation energy, which makes synthesis of the molecule difficult; Woodward and Hoffmann noted that prismane's thermal rearrangement to benzene is symmetry-forbidden, comparing it to "an angry tiger unable to break out of a paper cage."

On account of its strain energy and the aromatic stabilization of benzene, the molecule is estimated to be 90 kcal/mole less stable than benzene, but the activation of this highly exothermic transformation is a surprisingly high 33 kcal/mol, making it persistent at room temperature.