Kekule's structure of benzene. Diagram of the structure of the organic molecule benzene (C6.H6), as described in 1865 by the German chemist August Kekule (1829-1896). At the time it was known that benzene had a 1:1 ratio of carbon atoms (green) and hydrogen atoms (yellow), but no-one had yet proposed a satisfactory structure. Kekule proposed that the molecular structure was a ring of six carbon atoms, with one hydrogen atom for each carbon atom, and alternating double and single bonds in the ring. This establishment of the correct structure was crucial to the success of organic chemistry in the second half of the 19th century. The ring bonding was later refined by the concept of delocalisation.