Oxohalide

An oxohalide or oxyhalide is a type of chemical compound where an oxygen atom and halogen atom have chemical bonds to the same central atom of some other chemical element. They have the general chemical formula E_xO_yX_z. Oxohalides should not be confused with compounds related to halogen oxyacids like hypochlorites or perbromates, where the halogen is bonded to an oxygen atom.

Oxohalides are in the middle between oxides and halides. For any central element with a fixed oxidation state, it is possible to list some oxohalides by starting from the oxide and replacing each oxygen atom by two halogen atoms, one at a time. For example, for sulfur(VI) and fluorine:

SO₃ ⇌ SO₂F₂ ⇌ SOF₄ ⇌ SF₆

This is just a way to find the chemical formulae. There is not always a chemical reaction to change between oxides, oxohalides, and halides. There is also no guarantee that all of the compounds in this series are stable, or even exist. For example, silicon dioxide SiO₂ and silicon tetrachloride SiCl₄ are common compounds, but the oxychloride SiOCl₂ has only been seen as a short-lived reaction intermediate.

Carbon oxohalides

Carbon can form many different compounds with just oxygen and halogens. The functional group −COX is called an acyl halide, and is normally considered a derivative of a carboxylic acid −COOH. Acyl chlorides are the most common type of acyl halide, followed by acyl fluorides. Acyl halides get more unstable as the halogen gets heavier: acyl fluorides are generally the most stable, while acyl iodides are short-lived reaction intermediates made from acyl chlorides right before they are used.

Other compounds with just carbon, oxygen, and halogen, but without having the halogen and oxygen on the same carbon, are also sometimes called carbon oxohalides. An example is hexafluoroacetone, C₃F₆O.