 In 1856 Kekulé became Privatdozent at the University of Heidelberg.In 1858 he was hired as full professor at the University of Ghent, then in 1867 he was called to Bonn, where he remained for the rest of his career.Basing his ideas on those of predecessors such as Williamson, Edward Frankland, William Odling, Auguste Laurent, Charles-Adolphe Wurtz and others, Kekulé was the principal formulator of the theory of chemical structure (1857–58).