In 1900, Moses Gomberg reported the generation of the first organic free radical, the triarylmethyl radical. The radical was formed by reacting triarylmethyl chloride with silver metal in benzene.

Due to its reactivity toward oxygen, Gomberg did not isolate the triarylmethyl radical, but a yellow peroxide product. Despite this problem, Gomberg confidently proposed the formation of triarylmethyl radical, a trivalent carbon species. This concept received very strong criticism; Gomberg had to be on the defense for more than 10 years.

It was Wilhelm Schlenk who provided definitive evidence for the free radical concept. Schlenk prepared tris(biphenyl)methyl radical and isolated it as black crystals. In solution, this radical was almost completely monomeric.

• Thomas T. Tidwell, "The Gomberg Century: Free Radicals 1900-2000", Advances in Physical Organic Chemistry, 2001, 36, 1-58.
• Lennart Eberson, "Gomberg and the Nobel Prize", Advances in Physical Organic Chemistry, 2001, 36, 59-84.
• Thomas T. Tidwell, "Wilhelm Schlenk: The Man Behind the Flask", Angew. Chem. Int. Ed., 2001, 40, 331-337