Hypochlorous Acid, Where Have you Been all my Life?

I was thinking today, never during my chemical education have I encountered any kind of “halogen hydroxide,” HOX…at least not that I can remember. The chlorine version of this molecule is most certainly real however*, and goes by the name “hypochlorous acid.” It forms when chlorine gas is dissolved in water, and acts as a weak acid to give (slightly) the hypochlorite anion ClO.

Sadly, the compound cannot be isolated in pure form because it reacts with itself in light to form hydrochloric acid and oxygen gas. Its ionic brother Na(OCl), on the other hand, is the active ingredient in bleach. HOCl is used to form organic chlorohydrins and can also form disulfide bridges between proteins. HOBr, another hypohalous acid, exhibits similar reactivity.

At right is the HOMO (orbital no. 13) of HOCl, a π* orbital between chlorine and oxygen. According to B3LYP/6-311G(d,p), the total energy is -536 au and the molecule has vibrations at 692, 1238, and 3775 cm-1.

Coming soon…the ins and outs of QTAIM (and the matrix pictures)!

* The other HOX molecules also exist, but only HOF can be isolated purely.



  1. Quantum Theory of Atoms in Molecules! Seems simple but from the little bit I’ve read it looks very interesting.

    An example you’d like: According to Clar’s Rule phenanthrene is more stable than anthracene because of its extra aromatic sextet. Considering only Clar’s Rule, the steric hindrance between H’s in phenanthrene is destabilizing. But according to QTAIM, attraction of the H nuclei to the resulting broad electron cloud actually causes stabilization.

    QTAIM extends the molecular orbital concept by focusing on overall electron density and dividing it up among, well, “atoms in molecules.”


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