Stable organic free radicals cannot be isolated.

Nineteenth-century chemistry had already used the word radical for recurring groups of atoms within compounds. The harder question was whether a free radical could persist independently long enough to isolate, especially when the reactive center was carbon.

In 1900, Moses Gomberg was trying to prepare a highly substituted hydrocarbon when he obtained unexpected products. He proposed that the chemistry involved triphenylmethyl, a carbon-centered free radical.

The claim challenged accepted ideas about carbon valence and faced years of skepticism. Further experiments eventually established that persistent radicals were real chemical species rather than analytical mistakes or ordinary closed-shell molecules.

Their persistence is structural, not magical. Resonance can spread the unpaired electron across a molecule, while bulky groups can physically shield the reactive center and suppress the reactions that normally destroy radicals.

“Stable” is therefore relative. Many radicals exist for only fractions of a second; others can be prepared, stored, crystallized, and studied.

The discovery opened modern free-radical chemistry and showed that high reactivity does not automatically make isolation impossible.