Definition of Retinal
Retinal is also known as retinaldehyde. It was originally called retinene, and renamed after it was discovered to be vitamin A aldehyde. Retinal is one of the many forms of vitamin A (the number of which varies from species to species). Retinal is a polyene chromophore, bound to proteins called opsins, and is the chemical basis of animal vision. Retinal allows certain microorganisms to convert light into metabolic energy.
Vertebrate animals ingest retinal directly from meat, or they produce retinal from carotenoids, either from one of two carotenes (alpha-carotene, beta-carotene) or from beta-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, and 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.
IUPAC Name | (2E,4E,6E,8E)-3,7-Dimethyl-9-(2,6,6-trimethylcyclohexen-1-yl)nona-2,4,6,8-tetraenal |
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Other name | retinene; retinaldehyde; vitamin A aldehyde; RAL |
Chemical formula | C20H28O |
Molar mass | 284.44 g.mol-1 |
Melting pint | 61oC to 64oC;142oF to 147 oF; 334 K to 337 K |
Solubility in water | Nearly insoluble |
Solubility in fat | soluble |
Appearance | Orange crystals from petroleum ether |
Related compounds | retinol; retinoic acid; beta-carotene; dehydroretinal; 3-hydroxyretinal; 4-hydroxyretinal |
An aldehyde is an organic compound containing a functional group with the structure -CHO, consisting of a carbonyl center (a carbon double-bonded to oxygen) with the carbon atom also bonded to hydrogen and to an R group, which is any generic alkyl or side chain. The group without R- is the aldehyde group, also known as the formyl group. Aldehydes are common in organic chemistry. Many fragrances are aldehydes.