TCO ligation involves a [Diels-Alder reaction]() between a tetrazine and a trans-cyclooctene. The reaction proceeds through a [1,2,4-triazine intermediate]() and results in the formation of a stable dihydropyridazine product. The reaction is extremely fast, often occurring within seconds to minutes, and is highly selective, meaning it does not react with other functional groups commonly found in biological systems.
