Page "Friedrich August Kekulé von Stradonitz" Paragraph 5

Kekulé's idea of assigning certain atoms to certain positions within the molecule, and schematically connecting them using what he called their " Verwandtschaftseinheiten " (" affinity units ", now called " valences " or " bonds "), was based largely on evidence from chemical reactions, rather than on instrumental methods that could peer directly into the molecule, such as X-ray crystallography.

Such physical methods of structural determination had not yet been developed, so chemists of Kekulé's day had to rely almost entirely on so-called " wet " chemistry.

Some chemists, notably Adolph Wilhelm Hermann Kolbe, heavily criticized the use of structural formulas that were offered, as he thought, without proof.

However, most chemists followed Kekulé's lead in pursuing and developing what some have called " classical " structure theory, which was modified after the discovery of electrons ( 1897 ) and the development of quantum mechanics ( in the 1920s ).