Carbon oxohalide

Carbon oxohalides are a group of chemical compounds that contain only carbon, oxygen and halogen atoms: fluorine, chlorine, bromine and iodine. They include carbonyl halides, COX₂, and oxalyl halides, C₂X₂O₂, where X = F, Cl, Br or I. The halogen atoms X do not have to be identical; they differ in mixed oxohalides. Most combinations of halogens exist but carbonyl iodide, COI₂, is unknown. The carbon–oxygen bond length in carbonyl halides (1.13–1.17 Å)^[1] is shorter than in other carbonyl compounds^[2] such as aldehydes and ketones, carboxylic acids, esters and amides (1.20–1.21 Å).^[3] They are reactive reagents for halogenation,^[1] acylation and dehydration reactions.^[4]