Hypofluorous acid

Hypofluorous acid, chemical formula HOF, is the only known oxyacid of fluorine and the only known oxoacid in which the main atom gains electrons from oxygen to create a negative oxidation state. The oxidation state of the oxygen in this acid (and in the hypofluorite ion OF− and in its salts called hypofluorites) is 0, while its valence is 2. It is also the only hypohalous acid that can be isolated as a solid. HOF is an intermediate in the oxidation of water by fluorine, which produces hydrogen fluoride, oxygen difluoride, hydrogen peroxide, ozone and oxygen. HOF is explosive at room temperature, forming HF and O2:
 * 2 HOF → 2 HF + O2

This reaction is catalyzed by water.

It was isolated in the pure form by passing F2 gas over ice at −40 °C, rapidly collecting the HOF gas away from the ice, and condensing it:
 * F2 + H2O → HOF + HF

The compound has been characterized in the solid phase by X-ray crystallography as a bent molecule with an angle of 101°. The O–F and O–H bond lengths are 144.2 and 96.4 picometres, respectively. The solid framework consists of chains with O–H···O linkages. The structure has also been analyzed in the gas phase, a state in which the H–O–F bond angle is slightly narrower (97.2°).

Thiophene chemists commonly call a solution of hypofluorous acid in acetonitrile (generated in situ by passing gaseous fluorine through water in acetonitrile) Rozen's reagent.

Hypofluorites
Hypofluorites are formally derivatives of OF−, which is the conjugate base of hypofluorous acid. One example is trifluoromethyl hypofluorite (CF3OF), which is a trifluoromethyl ester of hypofluorous acid. The conjugate base is known in salts such as lithium hypofluorite.