Claus mostly worked in organic chemistry where his interests were very diverse and included alkaloids, aromatic substitution, oximes and theoretical considerations on the structure of organic molecules. Claus is best known for proposing a model of benzene molecule in 1867.[1]
In his model, the six carbon atoms of benzene form a hexagon with a hydrogen atom attached to every corner. To preserve valence 4 for carbons, the opposite corners of the hexagon are connected by single bonds.[2][3] It took years of research before the three postulated structures of benzene – by Albert Ladenburg (1869), August Kekulé 1865 and by Claus – found their place in organic chemistry. Ladenburg's prismane and Claus' benzene were both proven to be wrong. While the prismane was synthesized in 1973,[4] calculations showed that the synthesis of Claus' benzene is impossible.[5]
Claus synthesized and determined the structure of several isomers of oximes. He described the isomerism by differences in the bond structure of the molecules whereas several other scientists found it more convincing to describe the difference by the relatively new concept of stereochemistry. This scientific dispute lasted until his death in 1900.[1][2]
^Claus, Adolph K.L. (1867) "Theoretische Betrachtungen und deren Anwendungen zur Systematik der organischen Chemie" (Theoretical considerations and their applications to the classification scheme of organic chemistry), Berichte über die Verhandlungen der Naturforschenden Gesellschaft zu Freiburg im Breisgau (Reports of the Proceedings of the Scientific Society of Freiburg in Breisgau), 4 : 116-381. In the section Aromatischen Verbindungen (aromatic compounds), pp. 315-347, Claus presents Kekulé's hypothetical structure for benzene (p. 317), presents objections to it, presents an alternative geometry (p. 320), and concludes that his alternative is correct (p.326). See also figures on p. 354 or p. 379.
