What exactly is a quinone?

Question

And what about a hydroquinone?

Answer 1

It is a chemical term used to describe a molecule which contains a benzene ring with two double bonded oxygen atoms attached.  These are common in biological systems, and any molecule which contains a structure like this can be termed a 'quinone'  They do different things in different places depending on their structures.

Answer 2

One of a class of aromatic diketones in which the carbon atoms of the carbonyl groups are part of the ring structure. The name quinone is applied to the whole group, but it is often used specifically to refer to p-benzoquinone (1), o-Benzoquinone (2) is also known but the meta isomer does not exist.

Quinones are prepared by oxidation of the corresponding aromatic ring systems containing amino (NH2) or hydroxyl (OH) groups on one or both of the carbon atoms being converted to the carbonyl group.

Important naturally occurring naphthoquinones are vitamins K1 and K2 which are found in blood and are responsible for proper blood clotting reaction. A number of quinone pigments have been isolated from plants and animals. Illustrative of these are juglone found in unripe walnut shells and spinulosin from the mold Penicillium spinuhsum. 9,10-Anthraquinone derivatives form an important class of dyes of which alizarin is the parent type. p-Benzoquinone is manufactured for use as a photographic developer.