Semiquinone
From Wikipedia, the free encyclopedia
Semiquinones (or ubisemiquinones, if their origin is ubiquinone) are free radicals resulting from the removal of one hydrogen atom with its electron during the process of dehydrogenation of a hydroquinone, such as hydroquinone itself or catechol, to a quinone or alternatively the addition of a single hydrogen atom with its electron to a quinone.[1] Semiquinones are highly unstable.
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/b/b0/Semiquinon_mesomeric_xtd.png/640px-Semiquinon_mesomeric_xtd.png)
E.g. ubisemiquinone is the first of two stages in reducing the supplementary form of CoQ10 (ubiquinone) to its active form ubiquinol.