The theory was pioneered by Justus von Liebig, Friedrich Wöhler and Auguste Laurent around 1830 and is not related to the modern understanding of free radicals.
Jean-Baptiste Dumas proposed the ethylene radical from investigations into diethyl ether and ethanol.
Henri Victor Regnault in 1834 reacted ethylene dichloride (CH2CH2.Cl2) with KOH forming vinyl chloride, water, and KCl.
Radical theory replaced electrochemical dualism which stated that all molecules were to be considered as salts composed of basic and acidic oxides.
Liebig and Wöhler observed in 1832 [5] in an investigation of benzoin resin (benzoic acid) that the compounds almond oil (benzaldehyde), "Benzoestoff" (benzyl alcohol), benzoyl chloride and benzamide all share a common C7H5O fragment and that these compounds could all be synthesized from almond oil by simple substitutions.
[3] This law acknowledged that any hydrogen atom even as part of a radical could be substituted by a halogen.
In 1900 Moses Gomberg unexpectedly discovered true trivalent carbon and the first radical in the modern sense of the word in his (unsuccessful) attempt to make hexaphenylethane.
[14] In current organic chemistry, concepts such as benzoyl[15] and acetyl[16] persist in chemical nomenclature but only to identify a functional group having the same fragment.