Organic Chemistry 1 · Unsaturated molecules and radicals
Stereochemistry of alkene reactions: practice problems
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- 6-Oxoheptanal from 1-methylcyclohexene
- Open a three-membered bridge
- Use a neutral nucleophile
- Bromine addition — through a bromonium ion
- Add bromine to Z-but-2-ene
- Finish an anti chlorohydrin on a ring
- Finish an anti bromoether on a ring
- Prilezhaev epoxidation — E-but-2-ene
- Prilezhaev epoxidation — Z-but-2-ene
Draw the mechanism 115
- Open a three-membered bridgeConnect backside bridge opening to a trans vicinal dibromide.
- Use a neutral nucleophileTrack oxygen charge and anti stereochemistry during halohydrin formation.
- Bromine addition — through a bromonium ionMake a bromonium bridge, then open it from the opposite side to see how the E alkene determines the product stereochemistry.
- Add bromine to Z-but-2-eneMake a bromonium bridge, then open it from the opposite side to see how the Z alkene determines the product stereochemistry.
- Finish an anti chlorohydrin on a ringBuild a chloronium bridge and carry neutral water attack through deprotonation while retaining trans ring geometry.
- Finish an anti bromoether on a ringPreserve carbon configuration through alcohol capture and oxygen deprotonation in a complete ring-addition pathway.
- Prilezhaev epoxidation — E-but-2-eneDraw oxygen transfer from a peracid and see how E alkene geometry carries through to the epoxide.
- Prilezhaev epoxidation — Z-but-2-eneDraw oxygen transfer from a peracid and see how Z alkene geometry carries through to the epoxide.
- Prilezhaev epoxidation — followed by acidic ring openingCombine syn epoxide formation with acid-catalyzed backside opening to obtain a trans diol without omitting proton transfers.
- Prilezhaev epoxidation — followed by basic ring openingCarry styrene epoxidation into methoxide opening, selecting the carbon site and preserving the unbroken stereocenter during protonation.
- Hydroboration — syn addition of B–HUse the B–H bond and alkene π bond to add B and H from the same face in one step.
- Create alkene geometry from an anti conformerTranslate the specified anti-periplanar C–H/C–Br alignment into an E alkene through a complete E2 event.
- Add bromine across a five-membered ringCarry bromonium formation and backside bromide opening on cyclopentene through to a chiral trans dibromide and explain why it forms as a racemate rather than a meso compound.
- Epoxidize a trisubstituted ring alkene with mCPBADraw the four-pair mCPBA butterfly transfer to 1-methylcyclohexene and explain why the new quaternary stereocenter forms as a racemic cis-fused epoxide.
- Open a ring epoxide at its tertiary carbon in acidCombine acid activation, methanol attack at the more substituted epoxide carbon with inversion, and solvent deprotonation to obtain the trans 2-methoxy alcohol.
- Deliver two oxygens to one face with OsO₄Draw the concerted OsO₄ cycloaddition to cis-but-2-ene, track the reduction of osmium, and show that syn delivery to a Z alkene gives meso-butane-2,3-diol.
- Cleave an alkene with ozoneFollow ozonolysis of 2-methylbut-2-ene through molozonide formation, retro-cycloaddition to a carbonyl oxide, and recombination to the ozonide, then identify the carbonyl products of reductive workup.
- Make dichlorocarbene from chloroformGenerate :CCl₂ from chloroform by deprotonation and α-elimination, and describe the lone pair and empty orbital of the neutral six-electron carbon.
- Add dichlorocarbene to a Z alkeneDraw the concerted two-arrow addition of singlet dichlorocarbene to cis-but-2-ene and use its stereospecificity to identify the meso cis-cyclopropane.
- Replace boron by OH with retentionCarry an alkylborane from 1-methylcyclopentene through hydroperoxide addition, the 1,2-alkyl shift from boron to oxygen, and borate hydrolysis, keeping the C–O bond where the C–B bond was to give trans-2-methylcyclopentanol.
- trans-1-Methylcyclohexane-1,2-diol from the epoxideDraw the acid-catalysed hydrolysis of 1-methylcyclohexene oxide and explain why water attacks the tertiary carbon from the back side, giving the trans diol.
- Racemic hexane-3,4-diol from cis-2,3-diethyloxiraneOpen meso cis-2,3-diethyloxirane in aqueous acid with inversion at one carbon and show that the diol is the racemic (3R,4R)/(3S,4S) pair.
- trans-Cyclohexane-1,2-diol from cyclohexene oxideDraw protonation of cyclohexene oxide, backside attack of water on the protonated epoxide, and the final deprotonation that gives trans-cyclohexane-1,2-diol.
- trans-Cyclopentane-1,2-diol from cyclopentene oxideProtonate cyclopentene oxide, open it with backside attack of water and deprotonate to reach racemic trans-cyclopentane-1,2-diol.
- trans-Dibromide from 1,2-dimethylcyclopentene and Br₂Add bromine anti across 1,2-dimethylcyclopentene and decide whether the trans dibromide is chiral or meso.
- 1,2-Dibromohexane from hex-1-eneDraw bromonium-ion formation from hex-1-ene and bromide opening it from the back side to give 1,2-dibromohexane.
- trans-Dibromide from 1-methylcyclopentene and Br₂Bridge 1-methylcyclopentene with bromine and open the bromonium ion at its tertiary carbon to reach the trans dibromide.
- Racemic 1,2-dibromo-1,2-diphenylethane from (Z)-stilbeneShow that anti addition of bromine to (Z)-stilbene gives the chiral (R,R)/(S,S) dibromide pair rather than the meso compound.
- trans-1,2-Dibromocyclohexane from cyclohexene and Br₂Draw the bromonium ion of cyclohexene and its backside opening by bromide, and explain why no cis-1,2-dibromocyclohexane forms.
- trans-1,2-Dibromocyclooctane from cyclooctene and Br₂Add bromine across the cis ring alkene of cyclooctene and show why the two bromines end trans on the eight-membered ring.
- trans-1,2-Dibromocyclopentane from cyclopentene and Br₂Bridge cyclopentene with bromine and open the bromonium ion from the opposite face to reach racemic trans-1,2-dibromocyclopentane.
- 2,3-Dibromopentane from (E)-pent-2-ene and Br₂Track how anti addition of Br₂ to (E)-pent-2-ene fixes the relative configuration of 2,3-dibromopentane.
- (3R*,4S*)-3,4-Dibromoheptane from (E)-hept-3-eneAdd bromine anti to (E)-hept-3-ene and explain why the erythro dibromide is chiral even though the E-butene analogue is meso.
- meso-1,2-Dibromo-1,2-diphenylethane from (E)-stilbeneShow that anti addition of bromine to (E)-stilbene gives the meso dibromide, and why the bridged ion still forms despite two benzylic carbons.
- Bromoether from 1-methylcyclohexene in ethanolTrap the bromonium ion of 1-methylcyclohexene with ethanol and assign both the regiochemistry and the trans stereochemistry of the bromoether.
- 1-Bromo-2-methoxy-2-methylpropane from 2-methylpropeneLet methanol solvent trap the bromonium ion of 2-methylpropene at its tertiary carbon to form a bromoether.
- trans-1-Bromo-2-methoxycyclohexane (bromoether) from cyclohexeneTrap the cyclohexene bromonium ion with methanol instead of bromide and deprotonate the oxonium ion to reach racemic trans-1-bromo-2-methoxycyclohexane.
- Bromoether of styrene with Br₂ in methanolTrap the styrene bromonium ion with methanol at the benzylic carbon and deprotonate to reach (2-bromo-1-methoxyethyl)benzene.
- 1,2-Dibromopropane from propene and Br₂Add Br₂ to propene through a bromonium ion and explain why 1,2-dibromopropane forms as a racemate.
- trans-2-Bromo-1-methylcyclohexan-1-ol from 1-methylcyclohexeneCombine Markovnikov regiochemistry and anti stereochemistry in the bromohydrin of 1-methylcyclohexene.
- 1-Bromo-2-methylpropan-2-ol (bromohydrin) from 2-methylpropeneExplain why water opens the bromonium ion of 2-methylpropene at the tertiary carbon, giving 1-bromo-2-methylpropan-2-ol.
- 1-Bromo-3,3-dimethylbutan-2-ol from 3,3-dimethylbut-1-eneShow why the bromohydrin of 3,3-dimethylbut-1-ene forms without the methyl shift seen when the same alkene reacts through a free carbocation.
- 1-Bromo-2-phenylpropan-2-ol from α-methylstyreneOpen the bromonium ion of α-methylstyrene with water at its tertiary benzylic carbon to form the Markovnikov bromohydrin.
- trans-2-Bromocyclohexan-1-ol (bromohydrin) from cyclohexeneTrap the cyclohexene bromonium ion with water instead of bromide and deprotonate the oxonium ion to reach racemic trans-2-bromocyclohexan-1-ol.
- trans-2-Bromocyclopentan-1-ol from cyclopenteneTrap the cyclopentene bromonium ion with water and deprotonate the oxonium ion to reach racemic trans-2-bromocyclopentan-1-ol.
- erythro-4-Bromohexan-3-ol from (E)-hex-3-eneFollow anti addition of Br and OH across (E)-hex-3-ene and assign the erythro relative configuration of the bromohydrin.
- Anti bromohydrin of (E)-stilbene with Br₂ and waterOpen the (E)-stilbene bromonium ion with water from the back side and assign the erythro relative configuration of 2-bromo-1,2-diphenylethan-1-ol.
- 1-(Bromomethyl)cyclohexan-1-ol from methylenecyclohexaneOpen the bromonium ion of methylenecyclohexane with water at the ring carbon to give the Markovnikov bromohydrin.
- 2,3-Dibromopentane from (Z)-pent-2-ene and Br₂Track how anti addition of Br₂ to (Z)-pent-2-ene fixes the relative configuration of 2,3-dibromopentane.
- Anti bromination of (Z)-hept-3-ene to 3,4-dibromoheptaneAdd Br₂ across (Z)-hept-3-ene through a bromonium ion and use anti opening to decide that the dibromide is the racemic threo pair, not meso.
- trans-1,2-Dichlorocyclohexane from cyclohexene and Cl₂Draw chloronium-ion formation from cyclohexene and its backside opening by chloride to give racemic trans-1,2-dichlorocyclohexane.
- meso-2,3-Dichlorobutane from (E)-but-2-ene and Cl₂Follow the chloronium ion of (E)-but-2-ene to the meso dichloride and explain why anti addition gives an achiral product.
- 1-Chlorobutan-2-ol (chlorohydrin) from but-1-eneForm the chloronium ion of but-1-ene and let water open it at the secondary carbon to give the Markovnikov chlorohydrin.
- trans-Chlorohydrin from 1-methylcyclohexene and Cl₂/H₂OCombine Markovnikov regiochemistry and anti stereochemistry in the chlorohydrin of 1-methylcyclohexene.
- Racemic 2,3-dichlorobutane from (Z)-but-2-ene and Cl₂Follow the chloronium ion of (Z)-but-2-ene to the chiral dichloride pair and explain why no meso compound forms.
- trans-2-Bromocyclohexan-1-ol from cyclohexene oxideDraw HBr protonating cyclohexene oxide and bromide opening the protonated ring from the back side to give trans-2-bromocyclohexan-1-ol.
- cis-1,2-Diphenylcyclopropane from (Z)-stilbene (Furukawa)Draw the Furukawa carbenoid EtZnCH2I transferring CH2 to (Z)-stilbene in one step and explain why meso cis-1,2-diphenylcyclopropane is the only product.
- cis-1,2-Dimethylcyclohexane from 1,2-dimethylcyclohexeneShow schematically how both hydrogens of H2 are delivered from the catalyst surface to one face of 1,2-dimethylcyclohexene, giving cis-1,2-dimethylcyclohexane.
- trans-2-Methylcyclopentan-1-ol from 1-methylcyclopenteneDraw syn hydroboration of 1-methylcyclopentene, then HOO⁻ addition to boron, the alkyl shift with retention, and release of trans-2-methylcyclopentan-1-ol.
- (1-Bromo-2-iodoethyl)benzene from styrene and IBrUse the I–Br bond polarity and benzylic charge stabilisation to place both halogens when iodine monobromide adds to styrene.
- 2-Chloro-1-iodo-2-methylpropane from 2-methylpropenePlace iodine and chlorine correctly when iodine monochloride adds to 2-methylpropene through an iodonium ion.
- trans-1-Chloro-2-iodocyclohexane from cyclohexene and IClUse the polarity of iodine monochloride to form an iodonium ion of cyclohexene and open it anti with chloride.
- 2-Chloro-1-iodopropane from propene and IClDecide which end of iodine monochloride is the electrophile and where chloride opens the iodonium ion of propene.
- cis-1-Methylcyclohexane-1,2-diol with cold KMnO₄Dihydroxylate 1-methylcyclohexene with cold basic KMnO₄ and place the tertiary and secondary OH groups cis on the ring.
- cis-Cyclohexane-1,2-diol from cyclohexene and cold KMnO₄Draw the cyclic manganate ester from cyclohexene and cold basic KMnO₄ and show that its hydrolysis leaves both OH groups cis.
- cis-Cyclopentane-1,2-diol from cyclopentene and cold KMnO₄Draw the cyclic manganate ester from cyclopentene and permanganate and explain why cold, basic conditions give the cis diol rather than cleavage.
- Acetone and propanoic acid from 2-methylpent-2-eneDraw hot permanganate cleaving 2-methylpent-2-ene through the cyclic manganate ester, then oxidizing propanal to propanoic acid while acetone survives.
- Propanoic acid and CO2 from but-1-ene with hot KMnO4Draw hot permanganate cleaving but-1-ene and follow each fragment: the internal carbon to propanoic acid, the terminal CH2 all the way to carbon dioxide.
- Benzoic acid from (E)-stilbene with hot KMnO4Draw hot permanganate cleaving (E)-stilbene through the cyclic manganate ester and oxidizing both benzaldehyde fragments to benzoic acid.
- Epoxide of 1,2-dimethylcyclohexene with mCPBADraw the one-step butterfly transfer of oxygen from mCPBA to 1,2-dimethylcyclohexene and explain why the cis-fused epoxide is a single meso compound.
- mCPBA epoxidation of 1-methylcyclopenteneDraw the one-step butterfly oxygen transfer from mCPBA to 1-methylcyclopentene and explain why the epoxide ring fusion must be cis.
- Cyclohexene oxide from cyclohexene and mCPBADraw the four-arrow concerted oxygen transfer from mCPBA to cyclohexene and explain why the epoxide is necessarily cis-fused.
- Cyclopentene oxide from cyclopentene and mCPBAMove the four electron pairs of the butterfly transition state to turn cyclopentene into cyclopentene oxide, and decide whether the epoxide is chiral.
- trans-2-Methyl-3-phenyloxirane from (E)-1-phenylpropeneDraw the concerted transfer of oxygen from mCPBA to (E)-1-phenylpropene and show that the trans relationship of methyl and phenyl is kept in the epoxide.
- Trans-2,3-dimethyloxirane from (E)-but-2-eneDraw the one-step butterfly transfer of oxygen from mCPBA to (E)-but-2-ene and show that the trans methyl relationship survives in trans-2,3-dimethyloxirane.
- trans-2-Methyl-3-propyloxirane from (E)-hex-2-eneEpoxidize (E)-hex-2-ene with mCPBA in one step and show that the methyl and propyl groups end up trans on the epoxide ring.
- trans-Stilbene oxide from (E)-stilbene and mCPBATransfer oxygen from mCPBA to (E)-stilbene in one step and show that the trans phenyl relationship gives racemic trans-2,3-diphenyloxirane.
- Cis-2,3-dimethyloxirane from (Z)-but-2-eneDraw the one-step butterfly transfer of oxygen from mCPBA to (Z)-but-2-ene and show that the cis methyl relationship survives in cis-2,3-dimethyloxirane.
- cis-2-Methyl-3-propyloxirane from (Z)-hex-2-ene and MMPPUse the peroxy acid of MMPP to epoxidize (Z)-hex-2-ene in one step and explain why the cis epoxide is chiral yet racemic.
- meso-Hexane-3,4-diol from trans-2,3-diethyloxirane and NaOHOpen trans-2,3-diethyloxirane with hydroxide by backside SN2 attack, protonate the alkoxide with water and show that the diol is meso.
- 2-Bromo-1-phenylethan-1-ol from styrene with NBS and waterUse NBS as a Br⁺ source to make the styrene bromonium ion and show water opening it at the benzylic carbon.
- threo-4-Bromohexan-3-ol from (Z)-hex-3-ene and NBSUse NBS as the bromine source for a bromohydrin of (Z)-hex-3-ene and assign the threo product of anti addition.
- cis-1-Methylcyclopentane-1,2-diol from 1-methylcyclopenteneDraw the concerted [3+2] addition of OsO4 to 1-methylcyclopentene and hydrolysis of the cyclic osmate ester, keeping both C–O bonds to give cis-1-methylcyclopentane-1,2-diol.
- cis-1-Phenylcyclohexane-1,2-diol from OsO₄Add OsO₄ across trisubstituted 1-phenylcyclohexene and place the tertiary benzylic OH and the secondary OH cis in the racemic diol.
- meso-Butane-2,3-diol from (Z)-but-2-ene and OsO₄Follow syn dihydroxylation of (Z)-but-2-ene through the osmate ester and decide whether the diol is meso or racemic.
- cis-Cyclohexane-1,2-diol from cyclohexene and OsO₄Draw the one-step osmate-ester formation from cyclohexene and explain why the diol is cis.
- Racemic hexane-3,4-diol from (E)-hex-3-ene and OsO₄Dihydroxylate (E)-hex-3-ene with OsO₄ and decide that syn addition to the E alkene gives the racemic (3R,4R)/(3S,4S) diol.
- Racemic hydrobenzoin from (E)-stilbene and OsO₄Add both oxygens of OsO₄ to one face of (E)-stilbene and show that syn addition to the E alkene gives racemic (R,R)/(S,S)-hydrobenzoin.
- cis-Cycloheptane-1,2-diol from cycloheptene with OsO₄/NMOForm the osmate ester of cycloheptene with catalytic OsO₄, release cis-cycloheptane-1,2-diol and explain the role of NMO.
- (2R,3R)-Butane-2,3-diol from (E)-but-2-ene and OsO₄Follow syn dihydroxylation of (E)-but-2-ene through the osmate ester and decide whether the diol is meso or racemic.
- meso-Hexane-3,4-diol from (Z)-hex-3-ene with OsO₄/NMOUse catalytic OsO₄ with NMO to dihydroxylate (Z)-hex-3-ene and show that syn addition gives the single meso diol.
- meso-Hydrobenzoin from (Z)-stilbene with OsO₄/NMOFollow catalytic OsO₄/NMO syn dihydroxylation of (Z)-stilbene through the osmate ester and show why the diol is the single meso isomer.
- Octane-2,7-dione from 1,2-dimethylcyclohexeneFollow ozone through the tetrasubstituted ring alkene of 1,2-dimethylcyclohexene and the dimethyl sulfide workup to the diketone octane-2,7-dione.
- 6-Oxoheptanal from 1-methylcyclohexeneFollow ozonolysis of 1-methylcyclohexene through molozonide, carbonyl oxide and ozonide, then the dimethyl sulfide workup that opens the ring to the keto aldehyde 6-oxoheptanal.
- 5-Oxohexanal from 1-methylcyclopenteneDraw ozone cleaving the ring C=C of 1-methylcyclopentene and the dimethyl sulfide workup that gives the keto aldehyde 5-oxohexanal.
- Acetone and butanal from 2-methylhex-2-eneFollow ozone through 2-methylhex-2-ene to the ozonide and show how the dimethyl sulfide workup splits it into acetone and butanal.
- Acetone and formaldehyde from 2-methylpropeneFollow ozonolysis of 2-methylpropene through molozonide, carbonyl oxide and ozonide, then the dimethyl sulfide workup that releases acetone and formaldehyde.
- Hexanedial from cyclohexeneFollow ozonolysis of cyclohexene through the molozonide, the tethered carbonyl oxide and the ozonide, then the dimethyl sulfide workup that opens the ring to hexanedial.
- Succinaldehyde from (Z,Z)-cycloocta-1,5-dieneDraw excess ozone cleaving both alkenes of (Z,Z)-cycloocta-1,5-diene with a dimethyl sulfide workup: the ring opens, then the chain splits into two succinaldehyde molecules.
- Pentanedial from cyclopentene by ozonolysisDraw the ozonolysis of cyclopentene through molozonide, carbonyl oxide and ozonide, then the dimethyl sulfide workup that opens the ring to pentanedial.
- Two butanal from (E)-oct-4-ene by ozonolysisDraw the ozonolysis of symmetric (E)-oct-4-ene with a dimethyl sulfide workup and show why two equivalents of butanal form whatever the alkene geometry.
- 3-Acetyl-6-oxoheptanal from (R)-limonene by ozonolysisDraw excess ozone cleaving both alkenes of (R)-limonene, each through molozonide, carbonyl oxide and ozonide with a dimethyl sulfide workup, and track the untouched stereocentre.
- Cyclohexanone from methylenecyclohexane by ozonolysisDraw the ozonolysis of methylenecyclohexane and the dimethyl sulfide workup that gives cyclohexanone plus formaldehyde from the exocyclic CH2.
- Acetone and acetic acid from 2-methylbut-2-eneDraw the ozonolysis of 2-methylbut-2-ene with an oxidative hydrogen peroxide workup and show why the CH end becomes acetic acid while the other end stays acetone.
- Adipic acid from cyclohexene by oxidative ozonolysisDraw cyclohexene through ozonide formation and the hydrogen peroxide workup that turns both former CH carbons into carboxylic acids, giving adipic acid.
- Benzaldehyde from styrene: ozonolysis, Zn workupDraw the ozonolysis of styrene and the zinc and acetic acid workup that cleaves the ozonide to benzaldehyde and formaldehyde.
- Butanone and acetaldehyde from (Z)-3-methylpent-2-eneDraw the ozonolysis of (Z)-3-methylpent-2-ene with a dimethyl sulfide workup and explain why its E isomer would give the same butanone and acetaldehyde.
- meso cis-Stilbene oxide from (Z)-stilbene and peracetic acidDraw peracetic acid delivering one oxygen to (Z)-stilbene and decide why cis-2,3-diphenyloxirane is a single meso compound.
- 1-Methylbicyclo[4.1.0]heptane from 1-methylcyclohexeneDraw the Simmons–Smith carbenoid adding CH2 to 1-methylcyclohexene and explain why the product 1-methylbicyclo[4.1.0]heptane is cis-fused.
- cis-1,2-Dimethylcyclopropane from (Z)-but-2-eneDraw the Simmons–Smith carbenoid adding CH2 to (Z)-but-2-ene in one step and show why only cis-1,2-dimethylcyclopropane forms.
- Bicyclo[4.1.0]heptane from cyclohexeneDraw the one-step butterfly transfer of CH2 from the Simmons–Smith carbenoid ICH2ZnI to cyclohexene, giving cis-fused bicyclo[4.1.0]heptane.
- Cyclopropylbenzene from styrene by Simmons–SmithDraw the Simmons–Smith carbenoid adding CH2 to the vinyl group of styrene to give cyclopropylbenzene, and explain why the benzene ring does not react.
- trans-1,2-Dimethylcyclopropane from (E)-but-2-eneDraw the Simmons–Smith carbenoid adding CH2 to (E)-but-2-ene in one step and show why only trans-1,2-dimethylcyclopropane forms.
- 1-Ethyl-1,2-dimethylcyclopropane from (Z)-3-methylpent-2-eneAdd the Simmons–Smith carbenoid to the trisubstituted alkene (Z)-3-methylpent-2-ene and predict which diastereomer of 1-ethyl-1,2-dimethylcyclopropane forms.
- cis-1,2-Diethylcyclopropane from (Z)-hex-3-eneDraw the zinc carbenoid adding CH2 to (Z)-hex-3-ene in one concerted step and explain why the product is meso cis-1,2-diethylcyclopropane.
Predict the product 5
- Count the bromination productsDerive the enantiomeric outcome of anti addition to a Z alkene.
- Hot KMnO₄ cleavage of 2-methylbut-2-ene: name the productsPredict the oxidative cleavage products of a trisubstituted alkene with hot acidic permanganate.
- Fischer projection of the diol from OsO₄ + (E)-but-2-enePredict which butane-2,3-diol Fischer projection forms when OsO₄ adds syn to (E)-but-2-ene.
- Track deuterium labels: Br₂ + (Z)-1,2-dideuterioetheneUse deuterium labels to reveal the stereochemistry of bromine addition to a symmetric alkene.
- Open the epoxide in acidPredict the relative configuration of the diol from acid-catalysed epoxide hydrolysis.
Classify 3
- Spot the anti additionClassify alkene addition reagents as syn or anti additions.
- Is this hydrobenzoin Fischer projection meso?Classify a hydrobenzoin Fischer projection as meso or chiral and link it to the stilbene isomer that forms it with OsO₄.
- Meso or racemic diol?Decide whether syn dihydroxylation of (E)-pent-2-ene gives a meso compound or a racemic pair.
Compare 2
- Compare paired alkene experimentsRelate stereospecificity to substrate geometry.
- Can ozonolysis tell (E)- from (Z)-but-2-ene?Compare ozonolysis products of the two but-2-ene isomers and decide whether the reaction can reveal alkene geometry.
Calculate 5
- Check a tempting power-of-two answerApply molecular symmetry after a stereochemical reaction.
- How many stereoisomers from Br₂ + (E)-hex-3-ene?Count the stereoisomers formed when bromine adds anti across (E)-hex-3-ene.
- How many stereoisomers from Br₂ + (Z)-hex-3-ene?Count the 3,4-dibromohexane stereoisomers formed by anti addition of bromine to (Z)-hex-3-ene.
- Count diol stereoisomers: OsO₄ + 1,2-dimethylcyclopenteneCount the stereoisomers formed when OsO₄ adds syn to 1,2-dimethylcyclopentene, using the symmetry of the cis diol.
- How many dibromide stereoisomers?Count the stereoisomers formed when bromine adds anti to cyclohexene.
Find the error 2
- Find the missing stereochemical constraintDiagnose an unjustified syn claim for carbocation addition.
- Spot the error: OsO₄ + cyclopentene “gives the trans diol”Diagnose a wrong stereochemical claim about osmylation of a ring alkene and name the route that really gives the trans diol.
Interpret the evidence 4
- Read the planar starting drawingAssign E/Z before predicting stereochemical outcomes.
- Make invisible hydrogen delivery visibleUse isotopic labeling to observe syn addition on a ring.
- Fischer projection of the Br₂ + (E)-but-2-ene productMatch the anti-addition product of (E)-but-2-ene and bromine to its Fischer projection.
- Where does ¹⁸O go when cyclohexene oxide opens in H₂¹⁸O?Follow an ¹⁸O label through acid-catalysed opening of cyclohexene oxide to locate it in the trans diol.
Work backward 2
- Which C₇H₁₂ alkene gives heptane-2,6-dione on ozonolysis?Work backwards from a single dicarbonyl ozonolysis product to the cyclic alkene of formula C₇H₁₂.
- Which alkene was cleaved?Identify the alkene that gives a keto-aldehyde on reductive ozonolysis.
Plan a synthesis 4
- Choose the relative diol configurationChoose syn dihydroxylation rather than epoxide opening.
- Plan meso-hydrobenzoin from a stilbeneChoose every alkene and reagent pairing that gives meso-hydrobenzoin by matching syn or anti addition to alkene geometry.
- Make the cis diolChoose a reagent that converts cyclopentene into cis-cyclopentane-1,2-diol.
- Make the trans diolChoose a reagent sequence that converts cyclohexene into trans-cyclohexane-1,2-diol.
Explain why 3
- Know when equal-face reasoning failsIdentify the boundary of racemic predictions for achiral reagents.
- Order the steps of 1-methylcyclohexene bromohydrin formationSequence the events of bromohydrin formation from 1-methylcyclohexene, from bromine approach to the trans product.
- What makes it stereospecific?Explain why bromination of the but-2-ene isomers is called stereospecific.
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