The bonds C1–C2, C3–C4, C5–C6 and C7–C8 are about 1.36 Å (136 pm) in length, whereas the other carbon–carbon bonds are about 1.42 Å (142 pm) long.
Strukturo z dvema kondenziranima benzenovima obročema, ki jo je leta 1866 predpostavil Emil Erlenmayer, je tri leta kasneje potrdil Carl Gräbe.