IUPAC Name: Prismane
Synonyms of Prismane (CAS NO.650-42-0) : Ladenburg benzene ; Prismane ; Tetracyclo[2.2.0.02,6.03,5]hexane ; Triprismane
InChI:InChI=1/C6H6/c1-2-3(1)6-4(1)5(2)6/h1-6H
CAS NO:650-42-0
Molecular Formula:C₆H₆
Molecular Weight :78.1118
Molecular Structure :
Index of Refraction:1.834
Surface Tension: 76.4 dyne/cm
Density: 1.577 g/cm³
Enthalpy of Vaporization: 30.73 kJ/mol
Boiling Point: 79.8 °C at 760 mmHg
Vapour Pressure: 97 mmHg at 25°C 
Appearance: Prismane (CAS NO.650-42-0) is a colourless liquid.

Discussion about the structure of benzene in the mid 19th century yielded several structures for the formula C₆H₆, which was accessible by combustion analysis. The first, proposed by Kekulé in 1867, later proved to be the right one. This structure inspired several others to come up with concurring structures; for example, Ladenburg with prismane, Dewar with Dewar benzene, and Koerner and Claus with claus benzene. Some of these structures could be synthesized in the following years. Prismane, like the other proposed structures for benzene, is still often cited in the literature, because it is part of the historical struggle toward understanding the mesomeric structures and resonance of benzene. Some computational chemists still research the differences among the possible isomers of C₆H₆.

The synthesis starts from benzvalene (1) and 4-phenyltriazolidone, which is a strong dienophile. The reaction is a stepwise Diels-Alder like reaction, forming a carbocation as intermediate. The adduct (2) is then hydrolyzed under basic conditions and afterwards transformed into a copper(II) chloride derivative with acidic copper(II) chloride. Neutralized with a strong base, the azo compound (3) could be crystallized with 65% yield. The last step is a photolysis of the azo compound. This photolysis leads to a biradical which forms prismane (4) and nitrogen with a yield of less than 10%. The compound was isolated by preparative gas chromatography.

An explosive liquid. When heated to decomposition it emits acrid smoke and irritating fumes.

 Prismane (CAS NO.650-42-0) is explosive, which is unusual for a hydrocarbon. 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. The molecule in which all six hydrogens are substituted by methyl groups (hexamethylprismane) has a higher stability and was synthesized by rearrangement reactions in 1966.