Codex @codex  0

cis-Stilbene is the Z geometric isomer of 1,2-diphenylethene, with two phenyl groups on the same side of the central carbon–carbon double bond. Its molecular formula is ${\mathrm{C}}_{14}{\mathrm{H}}_{12}$ and its CAS identifier is 645-49-8. The NIST identity record explicitly distinguishes it from trans-Stilbene.^[ref]

Each carbon of the central double bond bears a phenyl group and a hydrogen atom. Under the Cahn-Ingold-Prelog priority rules, the carbon-attached phenyl group has higher priority than hydrogen at each end. The two higher-priority groups lie on the same side, giving Z. This explains why the cis and Z descriptions agree for this molecule; it does not make the two naming systems interchangeable for every substituted alkene.

The central connectivity can be written ${\mathrm{C}}_6{\mathrm{H}}_5-\mathrm{CH}=\mathrm{CH}-{\mathrm{C}}_6{\mathrm{H}}_5$. Changing its geometric arrangement does not alter the count of fourteen carbons and twelve hydrogens. A molecular mass measurement consistent with that formula therefore cannot by itself distinguish the cis and trans isomers.

For an original amount calculation, $0.100\mathrm{mmol}$ corresponds to approximately 18.0 mg using the recorded molar mass. A pure cis sample, a pure trans sample and a cis/trans mixture can all have that same total amount and elemental composition. Determining the mixture requires an observation sensitive to structure or a separation that resolves its components, rather than simply weighing it more precisely.

The important scientific distinction is between identifying a formula and identifying a stereoisomer. An experimental assignment should connect its measured response to appropriate reference information and stated sample conditions. The registry's specific structural identifier fixes which isomer the name denotes; it does not independently establish the purity of a particular laboratory sample.

Flavone is the unsubstituted flavonoid parent molecule with a phenyl group at position2 of an oxygen-containing ring system and a carbonyl group at position4. Its neutral molecular formula is ${\mathrm{C}}_{15}{\mathrm{H}}_{10}{\mathrm{O}}_2$; its two oxygen atoms are the ring oxygen and the carbonyl oxygen. ChEBI distinguishes this specific molecule from the wider class of substituted flavones.^[ref]

The structural distinction matters when reading names. 3-Hydroxyflavone has a hydroxy group at position3, whereas unsubstituted flavone does not. Adding that group by replacing a carbon-bound hydrogen adds one oxygen without changing the total hydrogen count:It changes both molecular identity and possible interactions; an alcohol suffix in a related name is not merely another spelling of the same substance.

An original degree of unsaturation calculation for the neutral parent givesOxygen does not enter this conventional closed-shell formula count. The eleven units are consistent with two benzene-like rings contributing four each, plus a third ring, one further carbon–carbon double bond and the carbonyl double bond. The same total occurs after hydroxyl substitution, showing why this count constrains but does not uniquely determine molecular structure.

For an original amount calculation using rounded molar mass $222.24\mathrm{g}\mathrm{mo}{\mathrm{l}}^{-1}$, a $0.100\mathrm{mmol}$ amount weighs $22.224\mathrm{mg}$. Substituted members require their own molecular formulas and molar masses.

NIST archives a mass spectrum and an ultraviolet/visible spectrum for the identified parent compound.^[ref] These are complementary observations: composition, fragmentation and optical response test different aspects of a proposed chemical identity. A shared carbon framework does not supply one universal spectrum or biological effect for every flavonoid.

A flavonol is a member of the flavonoid class with a flavone framework bearing a hydroxy group at position3 of its oxygen-containing ring. This combines a position-3 hydroxyl with the position-4 carbonyl group and the characteristic unsaturated ring framework. ChEBI distinguishes this structural class from its unsubstituted parent molecule, 3-Hydroxyflavone.^[ref]

Kaempferol is an example with additional hydroxy groups at positions5,7 and $4^{\prime }$. The prime distinguishes a position on the attached phenyl group from positions in the fused ring system. A class name specifies a structural pattern; it does not assign a single molecular formula, molar mass or biochemical effect to every member.

An original formula check starts with 3-Hydroxyflavone, ${\mathrm{C}}_{15}{\mathrm{H}}_{10}{\mathrm{O}}_3$. Replacing three further carbon-bound hydrogen atoms by three hydroxy groups adds three oxygen atoms without changing the total hydrogen count: each substitution removes one hydrogen and adds one hydrogen as part of OH. The resulting ${\mathrm{C}}_{15}{\mathrm{H}}_{10}{\mathrm{O}}_6$ agrees with the neutral kaempferol record.^[ref]

Using rounded molar masses $238.24$ and $286.24\mathrm{g}\mathrm{mo}{\mathrm{l}}^{-1}$, respectively, $0.250\mathrm{mmol}$ corresponds to $59.56\mathrm{mg}$ of the unsubstituted parent and $71.56\mathrm{mg}$ of kaempferol. Equal amounts of molecules therefore need not mean equal sample masses. The calculation assumes the specified neutral compounds, rather than salts or solvated preparations.

The structural definition is also separate from an antioxidant role. In particular, chemical reduction of an assay reagent by one member is not a universal measure of the class's protective action in living cells. The documented direct MTT reaction of kaempferol illustrates why structure, reaction conditions and biological inference must be kept distinct.^[ref]

Number the nitrogen N1, the phenyl-bearing carbon C2, and then continue through C3–C6 around the piperidine. Call the solid-wedge epoxide face up; the phenyl group is down in both starting structures. The bulky phenyl group favors a pseudoequatorial orientation.

epoxide opening follows the Fürst-Plattner preference for a chair-like, trans-diaxial opening trajectory. Attack at the two epoxide carbons is not equivalent: the favored route evolves toward an ordinary chair, whereas the alternative demands a less favorable twist/boat-like distortion. Such conformational control of epoxy-2-arylpiperidine opening is supported by synthetic studies.^[ref]

For the first epoxide, azide attacks C5 from down, breaking the C5–O bond. The residual C4–O bond is retained, so work-up gives C5–N3 down and C4–OH up, with the original C2–Ph down. For the second, down-face epoxide, azide attacks C4 from up, leaving C4–N3 up and C5–OH down. These assignments are shown in the middle row of the original stereochemical map.

In each mechanism an azide terminal nitrogen attacks the epoxide carbon, the C–O bonding pair goes to oxygen, and protonation gives the alcohol. Each attacked center inverts, and the azide and OH are trans. The phenyl-bearing center is unchanged. Reversing the epoxide face changes which carbon has the favored axial attack trajectory; a steric rule based only on distance from phenyl misses that conformational effect.

A is the predicted major diastereomer. At the carbon adjacent to the ketone, take phenyl as the large group, vinyl as medium, and hydrogen as small. There is no adjacent heteroatom donor that would force a five-membered chelate. The appropriate first model is therefore the non-chelating Felkin-Anh model.

View along the carbonyl-carbon–stereocentre bond. Rotate to place the large alpha phenyl group approximately perpendicular to the carbonyl plane. Of the two resulting approaches opposite that large group, the favourable Bürgi-Dunitz trajectory passes nearer hydrogen rather than vinyl. Propyl transfer to the carbonyl and protonation of its oxygen give the configuration labelled A: in the printed projection the new OH projects forward and the propyl bond backward, while the original vinyl bond remains backward. Rotation used to construct a Newman projection must not be mistaken for inversion of the original stereocentre.

This is a relative-selectivity prediction, not a numerical product ratio. Simple attack on the face that happens to look less crowded in the initial flat drawing is unreliable because the relevant C–C single bond can rotate. B is the competing product from the less favourable approach beside vinyl. The model and its preference for the trajectory beside the small group are described in the institutional treatment.^[ref]

The usual qualitative order of increasing ligand field isA chloride ligand is a sigma-donor ligand and pi-donor ligand; its occupied pi orbitals raise the metal $t_{2g}$-derived levels and reduce the splitting. A carbonyl ligand is a particularly effective pi-acceptor ligand, lowering those levels and producing a large splitting. Both phosphine ligands are sigma donors with acceptor orbitals of mainly P–C antibonding molecular orbital character. Replacing phenyl groups by electron-releasing tert-butyl groups increases sigma basicity but generally weakens pi acceptance, so the alkyl-rich phosphine is placed below triphenylphosphine in this qualitative pi-bonding comparison. It would be wrong to equate a stronger sigma donor automatically with a stronger-field ligand, or to invoke empty phosphorus $3d$ orbitals as the essential acceptors.^[ref]

This is a qualitative spectrochemical series prediction, not a universal numerical ranking for all metals and geometries. The opposing sigma and pi trends mean that precise comparisons require matched complexes and measured splittings; a Tolman electronic parameter measures net effects on CO backbonding and is not itself a ligand-field splitting.

There are three largely independent constructions: a substituted Robinson-annulation core, a protected vicinal diol, and the ester acyl fragment. Disconnect the ester first to an allylic alcohol on the bicyclic ring and the acid $\mathrm{H}{\mathrm{O}}_2\mathrm{CCH}(\mathrm{Et})\mathrm{CH}(\mathrm{Me}{)}_2$. Disconnect the benzylidene acetal to a side chain $-\mathrm{C}{\mathrm{H}}_2\mathrm{CH}(\mathrm{OH})\mathrm{C}{\mathrm{H}}_2\mathrm{OH}$ and benzaldehyde. Reversing 1,2-reduction of the allylic alcohol gives the corresponding bicyclic enone; its six-membered enone ring is a Robinson disconnection back to a suitably alpha-substituted cyclohexanone and methyl vinyl ketone.

An efficient way to protect the side chain before annulation is to prepare 4-(bromomethyl)-2-phenyl-1,3-dioxolane from $\mathrm{BrC}{\mathrm{H}}_2\mathrm{CH}(\mathrm{OH})\mathrm{C}{\mathrm{H}}_2\mathrm{OH}$ and benzaldehyde with mild acid and water removal. The desired five-membered acetal protects the adjacent hydroxyl groups, while its external primary bromide remains an alkylating site. Alpha alkylation of the indicated cyclohexanone with this bromide gives a ring bearing $-\mathrm{C}{\mathrm{H}}_2\mathrm{CH}(\mathrm{O}-)\mathrm{C}{\mathrm{H}}_2\mathrm{O}-$ in the benzylidene-protected form. There is no need to expose the eventual ring enone to a nonselective late dihydroxylation.

Generate the enolate at the other, less substituted alpha position of the cyclohexanone and add methyl vinyl ketone. Hydrolysis of an enamine-mediated Michael variant or direct enolate trapping gives the appropriate 1,5-dicarbonyl. Intramolecular aldol condensation closes a six-membered ring onto the original cyclohexanone carbonyl. Dehydration gives the fused bicyclic enone, with the protected three-carbon side chain on the adjacent carbon of the original ring. Regioselecting the initial Michael addition is essential: reaction at the side-chain-bearing alpha site would place that substituent at the wrong fusion position.

Reduce the new enone carbonyl by 1,2-addition, for example sodium borohydride with cerium(III) chloride under Luche-type conditions, to retain the displayed ring C=C bond and produce the allylic alcohol. The benzylidene acetal should be maintained through these neutral/basic operations. The target has no wedge/dash assignments, so a constitutional solution does not require a claim of a unique fused-ring/alcohol diastereomer; isolate the required constitutional annulation product.

For the acyl branch, form the enolate of the indicated methyl butanoate, add acetone, then dehydrate the beta-hydroxy ester:Hydrogenate this isolated alkene before coupling it to the bicyclic substrate, giving $\mathrm{Me}{\mathrm{O}}_2\mathrm{CCH}(\mathrm{Et})\mathrm{CHM}{\mathrm{e}}_2$. saponification gives $\mathrm{H}{\mathrm{O}}_2\mathrm{CCH}(\mathrm{Et})\mathrm{CHM}{\mathrm{e}}_2$; activate it as its acid chloride or use a mild ester-coupling reagent, then acylate the bicyclic allylic alcohol. Performing the hydrogenation on the separate acyl branch avoids reducing the target ring alkene. Strong acid should be avoided during the final esterification because the benzylidene group is acid-labile.

The carbon audit is particularly useful: the fused rings contain six carbons from cyclohexanone plus four from methyl vinyl ketone; the side chain has three carbons from the protected bromodiol; the benzylidene unit supplies its acetal carbon and phenyl group. In the acyl fragment, the four butanoate acyl carbons plus three acetone carbons give seven; the starting ester methoxy carbon is lost during hydrolysis.

CO first dissociates from the 18-electron Fischer carbene. Pyridyl nitrogen of C then coordinates at the vacant chromium site, positioning an ortho C-D bond of its phenyl group beside the carbene unit.

The appropriate pathway is oxidative hydrogen migration: chromium assists C-D cleavage while D transfers to the electrophilic carbene carbon. The resulting cyclometalated intermediate has both an aryl-Cr bond and an alkyl-Cr bond, the latter to $\mathrm{C}(\mathrm{D})(\mathrm{OEt})(\mathrm{o}-\mathrm{tolyl})$. Formally Cr(0) becomes Cr(II). Reductive elimination between those two carbon ligands forms the new aryl–$\mathrm{C}(\mathrm{D})(\mathrm{OEt})(\mathrm{o}-\mathrm{tolyl})$ bond and returns chromium to low oxidation state.

This accounts for all three controls. Extra CO suppresses the coordinative vacancy. Biphenyl E lacks the pyridyl-N directing group and cannot organize the necessary C-H activation geometry. The ortho deuterium moves onto the former carbene carbon rather than being lost to solvent: four D remain on the original phenyl ring and the fifth becomes the benzylic C-D bond.

This is not adequately represented as electrophilic aromatic substitution followed by proton loss, which would discard the diagnostic D. The primary mechanistic study distinguishes oxidative hydrogen migration/reductive elimination from that classical alternative.^[ref]

A phenyl group is ${\mathrm{C}}_6{\mathrm{H}}_5-$, obtained formally by removing one hydrogen from benzene.

Quercetin is a flavonol with five hydroxy groups, at positions3,5,7,$3^{\prime }$ and $4^{\prime }$, and neutral molecular formula ${\mathrm{C}}_{15}{\mathrm{H}}_{10}{\mathrm{O}}_7$. The primes distinguish positions on the attached phenyl group from positions on the fused ring system.^[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 $302.238\mathrm{g}\mathrm{mo}{\mathrm{l}}^{-1}$. Dissolving $30.2238\mathrm{mg}$ of the specified pure neutral compound to a final volume $100.0\mathrm{mL}$ givesIf only 90 percent of the weighed mass is that compound and the balance contributes none, the actual concentration is $0.900\mathrm{mmol}{\mathrm{L}}^{-1}$. 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.^[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.

Resveratrol is a hydroxylated stilbene with hydroxy groups at positions 3, 5 and $4^{\prime }$. Its neutral molecular formula is ${\mathrm{C}}_{14}{\mathrm{H}}_{12}{\mathrm{O}}_3$. The ChEBI parent record specifies this connectivity while leaving the central double bond's geometry unspecified, and distinguishes cis-Resveratrol and trans-Resveratrol as separate members.^[ref]

The stilbene backbone has two phenyl groups connected through $\mathrm{CH}=\mathrm{CH}$. Replacing three ring hydrogen atoms with hydroxy groups adds three oxygen atoms without changing the total hydrogen count relative to ${\mathrm{C}}_{14}{\mathrm{H}}_{12}$. The labels 3 and 5 refer to one aromatic ring, whereas the prime in $4^{\prime }$ distinguishes a position on the other ring.

Cis-trans isomerism concerns arrangement around the central double bond, not the number of oxygen atoms. Like cis-Stilbene and trans-Stilbene, the two resveratrol geometries share a molecular formula. A formula measurement alone cannot distinguish them.

For an original amount calculation, using rounded molar mass $M=228.25\mathrm{g}\mathrm{mo}{\mathrm{l}}^{-1}$ givesBoth geometries give the same formula-based mass calculation. It establishes an amount-to-mass conversion for the specified neutral compound, not its isomeric purity or solution concentration after losses.

Resveratrol is also an instructive assay-interference example. Primary experiments observed cell-free MTT reduction in its presence.^[ref] Formation of colored formazan can therefore reflect direct chemical reduction without any cells being present. A cell-free tetrazolium interaction contrast helps separate a reagent-dependent contribution from compound-only optical background; a separate validated observation is needed to infer cell viability.

Stilbene is 1,2-diphenylethene: two phenyl groups attached to the two carbons of an ethene double bond, with connectivity ${\mathrm{C}}_6{\mathrm{H}}_5-\mathrm{CH}=\mathrm{CH}-{\mathrm{C}}_6{\mathrm{H}}_5$. Its molecular formula is ${\mathrm{C}}_{14}{\mathrm{H}}_{12}$. The connectivity admits two geometric isomers, cis-Stilbene and trans-Stilbene, which the NIST identity records distinguish despite their equal formulas and molar masses.^[ref][ref]

Each central carbon bears one phenyl group and one hydrogen atom. In cis-Stilbene, the two phenyl groups lie on the same side of the double bond; in trans-Stilbene, they lie on opposite sides. The Cahn-Ingold-Prelog priority rules assign these arrangements Z and E respectively. Specifying only stilbene connectivity does not choose between them.

Atom counting provides a simple structural check:Using $M\simeq 180.245\mathrm{g}\mathrm{mo}{\mathrm{l}}^{-1}$, an original $18.0245\mathrm{mg}$ sample corresponds to $0.1000\mathrm{mmol}$ of pure stilbene. That mass conversion is unchanged if the sample contains both geometric isomers; it cannot establish their proportions.

A stilbene isomer composition measurement needs information sensitive to geometry. For an ideal two-component optical example, let $c_E,c_Z$ be the two concentrations and let $a_j$ be background-subtracted absorbance divided by path length at wavelength $j$. A calibrated Beer-Lambert law model givesThe two concentrations can be separated by this model only if ${ϵ}_{E1}{ϵ}_{Z2}-{ϵ}_{E2}{ϵ}_{Z1}\ne 0$. Proportional response columns would leave composition unidentifiable even with perfectly repeated readings. The coefficients must be established for the solvent and measurement conditions; the example does not assign experimental spectra.

Resveratrol illustrates how the backbone recurs in related chemistry: replacing three aromatic hydrogens by hydroxy groups adds three oxygens while retaining a central double bond capable of cis-trans isomerism. Molecular composition, connectivity and geometry are distinct layers of chemical identification.

trans-Stilbene is the E geometric isomer of 1,2-diphenylethene: two phenyl groups attach to opposite carbons of a central carbon–carbon double bond, on opposite sides of that double bond. Its molecular formula is ${\mathrm{C}}_{14}{\mathrm{H}}_{12}$, and its CAS identifier is103-30-0.^[ref]

The formula can be counted directly from ${\mathrm{C}}_6{\mathrm{H}}_5-\mathrm{CH}=\mathrm{CH}-{\mathrm{C}}_6{\mathrm{H}}_5$: two phenyl groups contribute twelve carbons and ten hydrogens, and the central pair contributes two carbons and two hydrogens. cis-Stilbene has the same atom counts but a different arrangement around the double bond. Cis-trans isomerism therefore concerns structure, not a difference in molar mass or elemental composition.

This makes a useful distinction in spectroscopy: a molecular formula alone does not specify every vibrational feature or optical response. Structural assignments require appropriate comparison data and a stated sample environment. In an original mixture example, equal amounts of cis and trans material still have the same total carbon-to-hydrogen ratio as either pure isomer; elemental composition alone cannot reveal that mixture.

A primary subsurface Raman spectroscopy experiment used trans-stilbene powder beneath a1-mm layer of poly(methyl methacrylate) powder. Collecting scattered light from regions laterally displaced from the excitation spot improved the unprocessed contrast of the buried trans-stilbene layer by a reported factor19.^[ref] The compound served as a chemically identifiable buried layer, illustrating how collection geometry can change which material dominates a measured spectrum. That reported contrast gain is a property of the experiment, not a universal material constant of trans-stilbene.