Iodine readily forms compounds with most other elements in the periodic table. It occurs most commonly in monovalent form with an oxidation state of –1. It forms relatively weak bonds with first-row elements, including carbon, the typical C–I bond dissociation energy being only about 55 kcal per mole. Organoiodine compounds have been used since the mid-1800s, notably in Wurtz coupling reactions, the Williamson ether synthesis, and Hofmann's alkylation of amines.