An isomer of benzene, C₆H₆. Dewar benzene has the systematic name bicyclo [2,2,0] hexa-2,5-diene, and is a nonplanar bicyclic molecule. It has a high bond strain and will spontaneously slowly convert to benzene. The unsubstituted compound was first synthesized in 1963. Although the existence of this isomer was postulated by Sir James Dewar in 1867, Dewar did not propose it as the true structure of benzene as he accepted the Kekulé structure.