Hypohalite

Hypohalites are chemical compounds containing the hypohalite ion, with the general formula XO⁻, where X is a halogen element from Group 17 of the periodic table (fluorine, chlorine, bromine, or iodine). Hypohalites are the conjugate bases of hypohalous acids (HOX) and represent the lowest oxidation state (+1) of halogens in their oxoanions.

Hypochlorite (ClO⁻)

Hypohalites are also encountered in organic chemistry, often as acyl hypohalites (see the Hunsdiecker reaction). Sodium hypohalite is used in the haloform reaction as a test for methyl ketones.^[1]

Structure

The hypohalite ion consists of a halogen atom covalently bonded to an oxygen atom, carrying an overall negative charge. The halogen is in the +1 oxidation state, and the oxygen is in the usual −2 state. The general formula is:

${\textstyle {\ce {XO-}}}$

• ${\displaystyle {\ce {X}}}$ is the halogen atom, and
• ${\displaystyle {\ce {O}}}$ is the oxygen atom

The Cl-O bond length in crystalline sodium hypochlorite pentahydrate, NaOCl·5H₂O, is 1.686 Å, while in sodium hypobromite pentahydrate, NaOBr·5H₂O, the Br–O bond length is 8% longer at 1.820 Å.^[2]

References

1. Experimental Organic Chemistry: A Miniscale and Microscale Approach by John Gilbert Stephen Martin p. 863
2. Topić, Filip; Marrett, Joseph M.; Borchers, Tristan H.; Titi, Hatem M.; Barrett, Christopher J.; Friščić, Tomislav (2021). "After 200 Years: The Structure of Bleach and Characterization of Hypohalite Ions by Single-Crystal X-Ray Diffraction". Angew. Chem. Int. Ed. 60 (46): 24400–24405. doi:10.1002/anie.202108843. PMID 34293249. S2CID 236199263.