alltrans

Alltrans is a term used across chemistry, biochemistry, and related fields to describe a molecular geometry in which every relevant double bond is in the trans configuration relative to the reference plane. The designation emphasizes a fully trans arrangement throughout a conjugated system or molecule, in contrast to cis or mixed configurations. The phrase is commonly written as all-trans or hyphenated as all-trans.

In chemistry and biochemistry, all-trans describes the geometry of polyenes and fatty acids. All-trans polyenes tend to be more linear and can exhibit different physical properties, such as higher melting points and distinct optical behavior, compared with their cis counterparts. In fatty acids, trans double bonds occur in some industrially hydrogenated fats, while natural trans fats also exist in small amounts in ruminant fats. The all-trans designation helps distinguish a fully trans chain from molecules with mixed cis/trans configurations.

In medicine, all-trans retinoic acid (ATRA) refers to a specific stereoisomer of retinoic acid. It is the all-trans form produced from vitamin A metabolism and is used clinically, notably in the treatment of acute promyelocytic leukemia. It is also used topically for acne and keratinization disorders. Other retinoic acid isomers, such as 9-cis and 13-cis forms, have different pharmacological profiles.

In materials science and spectroscopy, all-trans configurations influence the electronic structure and optical properties of conjugated polymers and chromophores, producing characteristic absorption features different from those of cis isomers.

The term is primarily a descriptive stereochemical label rather than a brand name. See also cis-trans isomerism, isomer, tretinoin, and hydrogenation.