High Quality Content by WIKIPEDIA articles! Prismane is a polycyclic hydrocarbon with the formula C6H6. It is an isomer of benzene, more specific: a valence isomer. Prismane is far less stable than benzene. The carbon (and hydrogen) atoms of the prismane molecule are arranged in the shape of a six-atom triangular prism. Albert Ladenburg proposed this structure for the compound now known as benzene. The compound was not synthesized until 1973.