Flavanone / flavone
Pinocembrin and chrysin are the same molecule apart from one bond. Pinocembrin is the flavanone: C15H12O4, 256.25 g/mol, CAS 480-39-7, with a saturated C2–C3 bond that makes carbon 2 a stereocentre and the molecule non-planar. Chrysin is the corresponding flavone: C15H10O4, 254.24 g/mol, CAS 480-40-0, with a C2=C3 double bond that removes the stereocentre and flattens the molecule.
They share the 5,7-dihydroxy A-ring and the unsubstituted B-ring, they occur together in poplar propolis, and they sit 2 amu apart. Everything that separates them follows from that single bond.
The difference
Set the two structures beside each other and the entire distinction is visible in a single position: the bond between carbon 2 and carbon 3. Everything else — the hydroxyls at positions 5 and 7, the unsubstituted B-ring, the ketone at position 4 — is identical.
Two hydrogens and one degree of unsaturation separate them — a mass difference of 2 amu. That is a small edit to write down and a large one to live with.
Consequences
Four properties follow from the saturation state, and each one can be measured independently of the others.
| Property | Pinocembrin (flavanone) | Chrysin (flavone) |
|---|---|---|
| C2–C3 bond | Saturated (single) | Unsaturated (double) |
| Carbon 2 | sp3, stereocentre | sp2, no stereocentre |
| Chirality | Two enantiomers; (2S) in nature | Achiral — a single entity |
| Geometry | C-ring puckered; molecule non-planar | Planar across all three rings |
| Conjugation | B-ring insulated from the C4 carbonyl | B-ring conjugated through to the carbonyl |
| Molecular formula | C15H12O4 | C15H10O4 |
| Molecular mass | 256.25 g/mol | 254.24 g/mol |
| CAS | 480-39-7 | 480-40-0 |
Primary sourceFormula, mass and CAS for both columns retrieved from PubChem, 29 August 2026.
MechanismIn a flavone the C2=C3 double bond sits between the B-ring and the C4 carbonyl, so the π system runs continuously from one end of the molecule to the other. In a flavanone that bridge is broken: the B-ring is an isolated benzene hanging off an sp3 carbon, electronically unaware of the ketone four atoms away.
This is why the two classes look different in an ultraviolet spectrum. Flavones and flavonols show a strong long-wavelength absorption — the band conventionally numbered I — arising from that extended conjugation. Flavanones largely lose it, leaving the shorter-wavelength band II from the A-ring benzoyl system as the dominant feature. A UV trace is therefore not merely a detection method here; it reports the saturation state directly.
LiteratureThe stereocentre at C2 is real, but it is not fixed. Flavanones sit in equilibrium with their ring-opened 2′-hydroxychalcone form, and that ring–chain interconversion passes through a planar, achiral intermediate. Base-catalysed cyclisation of 2′-hydroxychalcones is the standard synthetic route to flavanones precisely because the ring closes readily — and the same reversibility racemises the product.1 Racemisation rates for flavanones have been measured, and the thermodynamics of naringenin racemisation via the acyclic chalcone have been computed from the crystal structures of its enantiomers.2
In the plant, the enzyme chalcone isomerase closes the ring stereospecifically to give the (2S) product. Without it the reaction still runs spontaneously, but it delivers a racemate.3 The single enantiomer found in nature is therefore an enzymatic outcome rather than a thermodynamic one — the molecule has no intrinsic preference of its own to defend.
A phenolic flavanone is made water-soluble by deprotonating it — raising the pH until an aromatic hydroxyl gives up its proton and the molecule carries a charge. That is the obvious lever, and on the main page it is described as the one that simultaneously opens an oxidation route.
It opens a second route as well. Base is the catalyst for the ring-opening that racemises C2. So for this class of molecule, raising pH to gain solubility puts pressure on both the oxidation state and the stereochemistry at once — and a (2S) material that has quietly become racemic is no longer the substance a study specified. Chrysin, having no stereocentre, is untouched by this second failure and exposed only to the first.
Why the confusion persists
Pinocembrin and chrysin are not distant relatives that happen to resemble one another. They co-occur in poplar-type propolis, they are frequently reported together in the same analysis, and they are biosynthetically adjacent: the flavone is what the flavanone becomes when a desaturase removes the C2–C3 hydrogens.
Three practical consequences follow. A mass-spectrometric method resolving only nominal mass sees 256 and 254 and can conflate them with isotope peaks if the window is loose. A supplier certificate quoting “propolis flavonoids” without naming which one has specified nothing. And a literature claim about chrysin cannot be carried across to pinocembrin on grounds of structural similarity, because the property that most often carries flavonoid behaviour — planarity, and the conjugation that comes with it — is exactly what differs between them.
The wider family
Two independent edits generate the four principal poplar-propolis flavonoids: saturating or unsaturating C2–C3, and adding or omitting a hydroxyl at C3. Read across a row and you add one oxygen; read down a column and you remove two hydrogens.
| No 3-OH | With 3-OH | |
|---|---|---|
| C2–C3 saturated flavanone series |
Pinocembrin C15H12O4 · 256.25 · 480-39-7 flavanone; one stereocentre |
Pinobanksin C15H12O5 · 272.25 · 548-82-3 flavanonol; two stereocentres |
| C2=C3 unsaturated flavone series |
Chrysin C15H10O4 · 254.24 · 480-40-0 flavone; planar, achiral |
Galangin C15H10O5 · 270.24 · 548-83-4 flavonol; planar, achiral |
Primary sourceEvery formula, mass and CAS in this grid retrieved from PubChem, 29 August 2026. Nothing is carried over from secondary summaries.
The fifth major poplar-propolis phenolic does not belong in the grid at all. CAPE — caffeic acid phenethyl ester, C17H16O4, 284.31, CAS 104594-70-9 — is a phenylpropanoid ester rather than a flavonoid. It carries the catechol that none of the four above possesses, and it is substantially more polar. Its presence in the same resin is why a single extraction condition under-recovers: an eluent tuned to the flavonoid block is mismatched to CAPE, and the reverse. That problem is taken up on the propolis extraction page.
Telling them apart
Three orthogonal handles, in increasing order of what they settle.
The presence or absence of the long-wavelength band separates the flavanone series from the flavone series as classes. It is fast and it speaks directly to saturation state, but it does not distinguish pinocembrin from any other flavanone in the sample.
Roughly 2.016 Da apart at exact mass — a wide margin for any instrument reporting to three decimal places, and an invisible one for an instrument reporting to unit mass. What decides the answer here is not the sample but the resolution of the method used on it.
Only the flavanone has enantiomers, so only the flavanone splits into two peaks on a chiral stationary phase. This is the one test that answers a question the other two cannot: not merely which compound is present, but whether the (2S) material specified has come through processing as a single enantiomer.
A study reporting “pinocembrin” without stating stereochemistry has not fully specified its material, and stereoselective pharmacokinetic work on this compound exists precisely because two enantiomers need not behave alike.
Formulation
Neither compound has a basic nitrogen, so neither can be given a hydrochloride salt; that constraint is shared, and it is set out in full on the main page. What is not shared is what happens next.
Chrysin is planar and achiral. Its formulation problem is a solubility problem and an oxidation problem, and once those are handled the molecule that comes out is the molecule that went in.
Pinocembrin is neither planar nor achiral. It carries the same two problems plus a third: a stereocentre held in place by kinetics rather than by structure, and adjacent in mechanism to the very lever — pH — used to address the first. A process that reports purity by area percent and never looks at enantiomeric ratio can meet its own specification while the material drifts toward racemic.
That is why this page is more than a chemistry curiosity: the bond distinguishing the two compounds also distinguishes their manufacture.
Literature
Questions
In the formal sense that chrysin is pinocembrin minus two hydrogens, yes — it is the dehydro counterpart. In biosynthesis the conversion is an enzymatic desaturation of the C2–C3 bond, not an oxidation in the everyday sense of adding oxygen. The oxygen count is identical in both: four.
Chrysin has the larger literature overall, particularly in oral supplementation and hormone-related work. Pinocembrin has the more unusual record: a smaller body of work, but one that includes a national regulatory approval for ischaemic stroke and clinical dosing by the intravenous route. Volume of literature and depth of clinical progress are not the same measure.
No. Pinocembrin is 256.25 g/mol and chrysin 254.24 g/mol — 2 amu apart, corresponding to the two hydrogens removed when the C2–C3 bond becomes a double bond. On a unit-mass instrument that gap is easy to lose among isotope peaks; on an accurate-mass instrument it is unambiguous.
No. The differing property is planarity and the extended conjugation that accompanies it — frequently the property carrying the observed behaviour, whether in binding, stacking, redox chemistry or chromatographic retention. Structural similarity is a reason to test the second compound, not a reason to skip testing it.
The pathway exists: flavanones interconvert with their ring-opened chalcone form, and that route is base-catalysed and passes through an achiral intermediate. Whether it matters in a given process depends on the pH, temperature and time of that process, which is a measurement rather than an assumption. The point worth carrying is that the stereocentre is kinetically held rather than structurally locked — something to measure, not something to take for granted.
Two yes-or-no questions. Is the C2–C3 bond saturated? Saturated gives the flavanone series, unsaturated the flavone series. Is there a hydroxyl at C3? Adding one turns a flavanone into a flavanonol and a flavone into a flavonol. Pinocembrin, pinobanksin, chrysin and galangin are the four answers, and all four occur in poplar propolis.
Continue
