1865 – Belgium
‘Carbon is tetravalent and is capable of forming ring-type organic molecules’
In the 1860s scientists knew about the molecular formula of benzene, C6H6 , but they did not know how the six atoms are arranged in space. Kekule was the first chemist to suggest that carbon is tetravalent, that is, one carbon atom can combine with four atoms – he saw the possibility that the benzene molecule could be ring-shaped.
- Resonance_in_Benzene (wiki.chemprime.chemeddl.org)