Quinone

Quinone is 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 class includes some heterocyclic compounds.

The term quinone is also used more broadly to refer to the class of all cyclic conjugated triones. Quinones are produced by oxidation of quinols.

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 derived from quinine, an alkaloid that is oxidised to the quinone quinidine in the body.

Structure and bonding

Quinones are characterised by the presence of a carbonyl group in a six-membered aromatic ring. This carbonyl group can participate in hydrogen bonding with a hydrogen atom in a molecule of water, which makes quinones soluble in water. Quinones are also able to form hydrogen bonds with other molecules, and this ability makes them useful in biological systems.

Types of quinones

There are several types of quinones, including:

• Benzoquinone: Also known as cyclohexadienedione, this yellow-coloured compound is found in certain plants and fungi. It is used in the production of dyes and as a chemical intermediate in the production of pharmaceuticals.

• Naphthoquinone: This compound is found in many plants and fungi, and is used in the production of dyes and as a chemical intermediate in the production of pharmaceuticals.

• Anthraquinone: This compound is used in the production of dyes and is also used as a bird repellent.

• Plastoquinone: This quinone is involved in the electron transport chain in the light-dependent reactions of photosynthesis.

• Ubiquinone: Also known as coenzyme Q, this compound is found in all living organisms and plays a vital role in the production of ATP in cellular respiration.

Biological importance

Quinones play a crucial role in the biology of organisms. They are involved in electron transport in bacteria and in eukaryotic mitochondria and chloroplasts. They are also involved in the biosynthesis of many natural products.

See also

• Quinone methide
• Quinhydrone
• Hydroquinone
• Quinone reductase

References

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Quinone

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  Quinone Acidic Reduction
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  Ubiquinone