The quinones are a class of organic compounds that are formally "derived from aromatic compounds [such as benzene or naphthalene] by conversion of an even number of –CH= groups into –C(=O)– groups with any necessary rearrangement of double bonds, resulting in "a fully conjugated cyclic dione structure". The archetypical member of the class is 1,4-benzoquinone or cyclohexadienedione, often called simply "quinone" (thus the name of the class). Other important examples are 1,2-benzoquinone (ortho-quinone), 1,4-naphthoquinone and 9,10-anthraquinone. The name is derived from that of quinic acid (with the suffix "-one" indicating a ketone), since it is one of the compounds obtained upon oxidation of quinic acid. Quinic acid, like quinine is obtained from cinchona bark, called quinaquina in the indigenous languages of Peruvian tribes. Properties Quinones are oxidized derivatives of aromatic compounds and are often readily made from reactive aromatic compounds with electron-donating substituents such as phenols and catechols, which increase the nucleophilicity of the ring and contributes to the large redox potential needed to break aromaticity. (Quinones are conjugated but not aromatic). Quinones are electrophilic Michael acceptors stabilised by conjugation. Depending on the quinone and the site of reduction, reduction can either rearomatise the compound or break the conjugation. Conjugate addition nearly always breaks the conjugation. The term quinone is also used more generally for a large class of compounds formally derived from aromatic quinones through replacement of some hydrogen atoms by other atoms or radicals. Reactions Reduction Quinones are oxidizing agents, sometimes reversibly so. Relative to benzoquinone, more strongly oxidizing quinones include chloranil and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (also known as DDQ). The oxidizing power of quinones is enhanced by the presence of acids. In acidic conditions, quinone undergoes two-electron and two-proton reduction to hydroquinone. In alkaline conditions, quinones undergo a reversible single-step, two-electron reduction. In neutral conditions, quinones may undergo either a one-proton, two-electron reduction or a two-electron reduction. In aprotic media, quinones undergo two-step reduction without protons. In the first step, a short-lived semiquinone intermediate is formed. In the second step, the semiquinone is reduced into a quinone dianion. 9,10-Anthraquinone-2,7-disulphonic acid (AQDS) a quinone similar to one found naturally in rhubarb has been used as a charge carrier in metal-free flow batteries. Addition Quinones undergo addition reaction to form 1,4-addition products. An example of 1,4-addition reaction is the addition of hydrogen chloride to form chlorohydroquinone: Quinones can undergo Diels-Alder reactions. The quinone acts as the dienophile and reacts with a