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Names | |
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IUPAC name
Retinal
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Systematic IUPAC name
(2E,4E,6E,8E)-3,7-Dimethyl-9-(2,6,6-trimethylcyclohex-1-en-1-yl)nona-2,4,6,8-tetraenal | |
Other names
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Identifiers | |
3D model (JSmol)
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ChEBI | |
ChemSpider | |
ECHA InfoCard | 100.003.760 |
PubChem CID
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UNII | |
CompTox Dashboard (EPA)
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Properties | |
C20H28O | |
Molar mass | 284.443 g·mol−1 |
Appearance | Orange crystals from petroleum ether[1] |
Melting point | 61 to 64 °C (142 to 147 °F; 334 to 337 K)[1] |
Nearly insoluble | |
Solubility in fat | Soluble |
Related compounds | |
Related compounds
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retinol; retinoic acid; beta-carotene; dehydroretinal; 3-hydroxyretinal; 4-hydroxyretinal |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Retinal (also known as retinaldehyde) is a polyene chromophore. Retinal, bound to proteins called opsins, is the chemical basis of visual phototransduction, the light-detection stage of visual perception (vision).
Some microorganisms use retinal to convert light into metabolic energy. In fact, a recent study suggests most living organisms on our planet ~3 billion years ago used retinal to convert sunlight into energy rather than chlorophyll. Since retinal absorbs mostly green light and transmits purple light, this gave rise to the Purple Earth Hypothesis.[2]
Retinal itself is considered to be a form of vitamin A when eaten by an animal. There are many forms of vitamin A, all of which are converted to retinal, which cannot be made without them. The number of different molecules that can be converted to retinal varies from species to species. Retinal was originally called retinene,[3] and was renamed[4] after it was discovered to be vitamin A aldehyde.[5][6]
Vertebrate animals ingest retinal directly from meat, or they produce retinal from carotenoids — either from α-carotene or β-carotene — both of which are carotenes. They also produce it from β-cryptoxanthin, a type of xanthophyll. These carotenoids must be obtained from plants or other photosynthetic organisms. No other carotenoids can be converted by animals to retinal. Some carnivores cannot convert any carotenoids at all. The other main forms of vitamin A — retinol and a partially active form, retinoic acid — may both be produced from retinal.
Invertebrates such as insects and squid use hydroxylated forms of retinal in their visual systems, which derive from conversion from other xanthophylls.