Retinal

All-trans-retinal

Names
IUPAC name Retinal
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 Retinene Retinaldehyde Vitamin A aldehyde RAL
Identifiers
CAS Number	116-31-4 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:17898
ChemSpider	553582
ECHA InfoCard	100.003.760
PubChem CID	638015
UNII	RR725D715M Y
CompTox Dashboard (EPA)	DTXSID5025998
InChI InChI=1S/C20H28O/c1-16(8-6-9-17(2)13-15-21)11-12-19-18(3)10-7-14-20(19,4)5/h6,8-9,11-13,15H,7,10,14H2,1-5H3/b9-6+,12-11+,16-8+,17-13+ Key: NCYCYZXNIZJOKI-OVSJKPMPSA-N
SMILES CC1=C(C(CCC1)(C)C)/C=C/C(=C/C=C/C(=C/C=O)/C)/C
Properties
Chemical formula	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]
Solubility in water	Nearly insoluble
Solubility in fat	Soluble
Related compounds
Related compounds	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). Y verify (what is YN ?) Infobox references

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.