= Quercetin
{title2=$\mathrm{C_{15}H_{10}O_7}$}
\b[<Quercetin>] is a <flavonol> with five <hydroxy groups>, at positions3,5,7,$3'$ and $4'$, and neutral <molecular formula> $\mathrm{C_{15}H_{10}O_7}$. The primes distinguish positions on the attached <phenyl group> from positions on the fused ring system.<Quercetin in ChEBI>[CHEBI:16243, definition, formula and structure]{ref}
Five hydroxyl oxygens account for only five of the seven oxygen atoms: the <flavone> framework also contains a ring oxygen and a <carbonyl group>. Compared with <kaempferol>, the additional hydroxyl substitution adds one oxygen without changing the total hydrogen count, because a carbon-bound hydrogen is replaced by OH. Counting elemental composition is a useful structural check, but does not locate the groups without connectivity information.
An original solution calculation uses the average <molar mass> $302.238\,\mathrm{g\,mol^{-1}}$. Dissolving $30.2238\,\mathrm{mg}$ of the specified pure neutral compound to a final volume $100.0\,\mathrm{mL}$ gives
$$
c=\frac{0.0302238/302.238}{0.1000}=0.001000\,\mathrm{mol\,L^{-1}}.
$$
If only 90 percent of the weighed mass is that compound and the balance contributes none, the actual <concentration> is $0.900\,\mathrm{mmol\,L^{-1}}$. Salt form, retained solvent or incomplete dissolution require their own corrections; the molecular formula alone does not establish preparation purity.
<Pradeep K. Sengupta> and <Michael Kasha> included <quercetin> in their early study of unusual <fluorescence> from <flavonols>, connecting its optical behaviour with excited-state <proton transfer>.<Excited state proton-transfer spectroscopy of 3-hydroxyflavone and quercetin by Pradeep K. Sengupta and Michael Kasha>[1979, printed pp.382–384, molecular comparison and spectroscopy]{ref} Chemical identity, absorption and emission conditions matter when interpreting a signal. Classification as an <antioxidant> does not, by itself, establish protection of living <cells> or a clinical effect.
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