= All-trans-retinol
<All-trans-retinol> is the form of <retinol> whose four acyclic <double bonds> have trans, or $E$, geometry. Its <molecular formula> is $\mathrm{C_{20}H_{30}O}$, and it retains the <alcohol> group characteristic of retinol. The prefix fixes double-bond geometry; it does not specify one frozen <conformation> about every <single bond>.<All-trans-retinol in ChEBI>[CHEBI:17336, Definition and Formula]{ref}
The distinction from <11-cis-retinol> illustrates why elemental composition is incomplete structural information. Both have the same formula, while one specified double bond has different geometry. A mass measurement consistent with that formula cannot on its own identify which isomer is present.
A second distinction concerns the <alcohol> group. <Lecithin retinol acyltransferase> can convert retinol into a <retinyl ester> by transferring an <acyl group>. Changing ester status and changing cis–trans geometry are separate chemical operations.<Lecithin retinol acyltransferase in IUBMB Enzyme Nomenclature>[EC 2.3.1.135, reaction and acceptor]{ref}
For example, an assay that pools all vitamin-A-related signals could register material before and after esterification without resolving the conversion. An interpretable experiment names the chemical form and the structural distinction being measured, rather than inferring identity solely from a shared <retinoid> classification.
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