 Estriol

Estriol is an estrogen with three hydroxy groups on its steroid framework, at positions 3, 16 and 17 in the conventional numbering. The usual compound has the specified $16\alpha ,17\beta$ arrangement and molecular formula ${\mathrm{C}}_{18}{\mathrm{H}}_{24}{\mathrm{O}}_3$. Chemical identity includes this spatial arrangement, rather than only a list of constituent elements.^[ref]

The structure provides an illuminating comparison with estrone, whose formula is ${\mathrm{C}}_{18}{\mathrm{H}}_{22}{\mathrm{O}}_2$. The two compounds share an eighteen-carbon framework but differ in functional groups and hydrogen count. Equal carbon count does not make them the same molecule, and a shared estrogen classification does not imply equal activity in every assay.

Using the database's average molar mass of $288.387\mathrm{g}\mathrm{mo}{\mathrm{l}}^{-1}$, an illustrative $1\mathrm{nmol}$ sample has mass $288.387\mathrm{ng}$ by $m=nM$. This converts amount to mass without predicting a physiological response. A comparison of hormonal effects must additionally specify the experimental system and exposure, rather than infer potency from mass alone.^[ref]