Hydroquinone, or quinol, is a phenolic compound, consisting of
benzene with
hydrogen atoms 1 and 4 replaced by
hydroxyl groups, -OH. It could be called by a number of systematic names, including 1,4-benzenediol, benzene-1,4-diol, p-benzenediol, 1,4-dihydroxybenzene, p-dihydroxybenzene, 4-hydroxyphenol, and p-hydroxyphenol. This tells you something about the delights of organic
nomenclature.
It looks like this:
H
|
C
/ \
H - C C - O - H
| O |
H - O - C C - H
\ /
C
|
H
According to
Chambers Science and Technology Dictionary it is a strong
reducing agent and is used extensively as a developer in
photography.
Other assorted data: it can brown apples and is one of the chemicals used by the bombardier beetle in its defence system. rp informs me that it is also used as a whitener in body milk.