Liebig and Wöhler observed in 1832  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 CHO fragment and that these compounds could all be synthesized from almond oil by simple substitutions. The CHO fragment was considered a "radical of benzoic acid" and called benzoyl. Organic radicals were thus placed on the same level as the inorganic elements. Just like the inorganic elements (simple radicals) the organic radicals (compound radicals) were indivisible. The theory was developed thanks to improvements in elemental analysis by von Liebig. Laurent contributed to the theory by reporting the isolation of benzoyl itself in 1835, however the isolated chemical is today recognised at its dimer dibenzoyl. Raffaele Piria reported the salicyl radical as the base for salicylic acid. Liebig published a definition of a radical in 1838 
Berzelius and Robert Bunsen investigated the radical cacodyl (reaction of cacodyl chloride with zinc) around 1841, now also known as a dimer species (CH)As—As(CH). Edward Frankland and Hermann Kolbe contributed to the radical theory by investigating the ethyl and the methyl radicals. Frankland first reported diethylzinc in 1848. Frankland and Kolbe together investigated the reaction of ethyl cyanide and zinc in 1849  reporting the isolation of not the ethyl radical but the methyl radical (CH) which in fact was ethane. Kolbe also investigated the electrolysis of potassium salts of some fatty acids. Acetic acid was regarded as the combination of the methyl radical and oxalic acid and electrolysis of the salt yielded as gas again ethane misidentified as the liberated methyl radical.
In 1850 Frankland investigated ethyl radicals. In the course of this work butane formed by reaction of ethyl iodide and zinc was mistakenly identified as the ethyl radical.