<Retinol> is a <retinoid> with an alcohol end group and molecular formula $\mathrm{C_{20}H_{30}O}$. A general structural description does not specify the geometry of every double bond: <all-trans-retinol> and <11-cis-retinol> distinguish particular configurations of the same framework.<Retinol in ChEBI>[CHEBI:50211, Definition, Formula and stereoisomer relationships]{ref}

That distinction matters because molecular formula and molecular geometry answer different questions. Two samples can have the same elemental composition while containing different proportions of <retinol> isomers. Their identical nominal molecular masses do not make those samples chemically interchangeable.

The alcohol group also distinguishes <retinol> from <retinyl esters>. <Lecithin retinol acyltransferase> transfers an <acyl group> onto the alcohol oxygen, producing an ester form that participates in storage and <retinoid> metabolism.<Lecithin retinol acyltransferase in IUBMB Enzyme Nomenclature>[EC 2.3.1.135, reaction and comments]{ref}

For a simple amount-to-mass example, the average <molar mass> $286.459\,\mathrm{g\,mol^{-1}}$ gives $286.459\,\mathrm{ng}$ for $1\,\mathrm{nmol}$ of <retinol>. This calculation specifies total chemical amount, without identifying its isomer distribution or biological availability.<Retinol in ChEBI>[Formula and Average Mass]{ref}


 Retinol (source code)