"German chemist Friedrich August Kekulé published a paper in French suggesting that the structure contained a six-membered ring of carbon atoms with alternating single and double bonds. Kekulé used evidence that there always appeared to be only one isomer of any monoderivative of benzene, and that there always appeared to be exactly three isomers of every diderivative—now understood to correspond to the ortho, meta, and para patterns of arene substitution—to argue in support of his proposed structure. Kekulé's symmetrical ring could explain these curious facts, as well as benzene's 1:1 carbon-hydrogen ratio. In 1890 the German Chemical Society organized a celebration of the 25th anniversary of his first benzene paper; Kekulé said that he had discovered the ring shape of the benzene molecule after having a reverie or day-dream of a snake seizing its own tail." - Adriano