Organic Chemistry 1 · Exam review
Alkene and alkyne reactions: exam review: practice problems
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- Ethynide adds to cyclohexanone
- Deprotonation and methylation of 3,3-dimethylbut-1-yne
- Anti addition of bromine to cyclohexene
- Chlorohydrin formation from propene
- Acid-catalysed tautomerisation of an alkyne-hydration enol
- Epoxidation of cyclooctene with mCPBA
- Acid-catalysed hydrolysis of cyclopentene oxide
- HBr adds to 2-methylbut-1-ene
- HBr adds to vinylcyclohexane with a hydride shift
Draw the mechanism 61
- Ethynide adds to cyclohexanoneDraw deprotonation of ethyne by amide ion, addition of the ethynide ion to the carbonyl carbon of cyclohexanone, and protonation of the alkoxide by ammonium ion on workup to give 1-ethynylcyclohexan-1-ol.
- Deprotonation and methylation of 3,3-dimethylbut-1-yneDraw deprotonation of 3,3-dimethylbut-1-yne by amide ion and SN2 attack of the acetylide on iodomethane to give 4,4-dimethylpent-2-yne.
- Anti addition of bromine to cyclohexeneDraw bromonium-ion formation from cyclohexene and Br2, then backside opening by bromide, and explain why the product is racemic trans-1,2-dibromocyclohexane.
- Chlorohydrin formation from propeneDraw chloronium-ion formation from propene, opening by water at the more substituted carbon, and deprotonation to give 1-chloropropan-2-ol.
- Acid-catalysed tautomerisation of an alkyne-hydration enolDraw the acid-catalysed conversion of the enol formed by Markovnikov hydration of 3-methylbut-1-yne into 3-methylbutan-2-one: carbon protonation by hydronium, then O–H deprotonation by water.
- Epoxidation of cyclooctene with mCPBADraw the concerted one-step oxygen transfer from mCPBA to cyclooctene, tracking all four electron pairs, to give cyclooctene oxide and 3-chlorobenzoic acid.
- Acid-catalysed hydrolysis of cyclopentene oxideDraw protonation of cyclopentene oxide, backside attack of water at one epoxide carbon, and deprotonation, and explain why the second stage of anti dihydroxylation gives trans-cyclopentane-1,2-diol.
- HBr adds to 2-methylbut-1-eneDraw the two-step ionic addition of HBr to 2-methylbut-1-ene: protonation that gives the tertiary carbocation, then capture by bromide to give 2-bromo-2-methylbutane.
- HBr adds to vinylcyclohexane with a hydride shiftDraw Markovnikov protonation of vinylcyclohexane, the 1,2-hydride shift that turns the secondary cation into a tertiary ring cation, and capture by bromide to give 1-bromo-1-ethylcyclohexane.
- Acid-catalysed hydration of 1-ethylcyclohexeneDraw the acid-catalysed hydration of 1-ethylcyclohexene: protonation by hydronium to the tertiary cation, attack by water, and deprotonation by water to give 1-ethylcyclohexan-1-ol with the acid regenerated.
- Hydroboration–oxidation of 2-methylpent-1-eneDraw concerted syn hydroboration of 2-methylpent-1-ene with boron on the CH2 carbon, then the oxidation steps that replace boron by OH, giving the anti-Markovnikov alcohol 2-methylpentan-1-ol.
- Acid-catalysed addition of methanol to 2,3-dimethylbut-2-eneDraw the acid-catalysed addition of methanol to 2,3-dimethylbut-2-ene: protonation by protonated methanol, capture of the tertiary cation by methanol, and deprotonation that regenerates the acid and gives 2-methoxy-2,3-dimethylbutane.
- OsO4 dihydroxylation of 1,2-dimethylcyclohexeneDraw the concerted cycloaddition of OsO4 to 1,2-dimethylcyclohexene that forms the cyclic osmate(VI) ester, track the reduction of osmium, and predict the meso cis diol released on workup.
- Oxymercuration of 3-methylbut-1-eneDraw ionisation of mercury(II) acetate, formation of the bridged mercurinium ion, opening by water at the more substituted carbon, and deprotonation, and explain why oxymercuration gives 3-methylbutan-2-ol without the rearrangement seen in acid-catalysed hydration.
- Ozonolysis of (E)-3-methylpent-2-eneDraw ozone cycloaddition to (E)-3-methylpent-2-ene, fragmentation of the primary ozonide into a carbonyl compound and a carbonyl oxide, and their recombination to the ozonide, then predict the carbonyl products after dimethyl sulfide workup.
- Ethynylcyclohexane alkylation with 1-bromopropaneDraw deprotonation of ethynylcyclohexane by amide ion, then SN2 attack of the cyclohexylacetylide ion on 1-bromopropane, giving pent-1-yn-1-ylcyclohexane.
- Br2 anti addition to 1-phenylcyclohexeneDraw the bromonium ion from 1-phenylcyclohexene and its back-side opening by bromide at the phenyl-bearing carbon, giving trans-1,2-dibromo-1-phenylcyclohexane.
- Bromination of (E)-hex-3-ene to meso-3,4-dibromohexaneDraw the bridged bromonium ion from (E)-hex-3-ene and its backside opening by bromide, giving meso-3,4-dibromohexane by anti addition.
- Bromohydrin from hex-1-ene: 1-bromohexan-2-olDraw the bromonium ion from hex-1-ene, water opening it at C2 (the more substituted carbon), and loss of the proton to give 1-bromohexan-2-ol.
- Br2 anti addition to (Z)-1-phenylpropeneDraw the cis bromonium ion from (Z)-1-phenylpropene and its back-side opening by bromide at the benzylic carbon, giving racemic (1R*,2R*)-1,2-dibromo-1-phenylpropane.
- Bromohydrin from 1-methylcyclopentene: anti additionDraw the bromonium ion from 1-methylcyclopentene, anti attack of water at the methyl-bearing carbon, and deprotonation to trans-2-bromo-1-methylcyclopentan-1-ol.
- Bromohydrin from (E)-β-methylstyreneDraw the trans bromonium ion from (E)-β-methylstyrene, its anti opening by water at the benzylic carbon, and deprotonation, giving racemic (1R*,2S*)-2-bromo-1-phenylpropan-1-ol.
- D2 and Pd/C on cyclohexene: syn deuterationDraw oxidative addition of D2 to palladium, insertion of cyclohexene into a Pd–D bond and reductive elimination, showing that syn delivery gives meso cis-1,2-dideuteriocyclohexane.
- Pent-1-yne from 1,2-dibromopentane by double eliminationDraw two E2 eliminations of HBr from 1,2-dibromopentane by amide ion, deprotonation of the terminal alkyne by a third amide ion, and protonation by water in the workup to give pent-1-yne.
- Disiamylborane hydroboration of 4-ethynylanisoleDraw syn hydroboration of 4-ethynylanisole by disiamylborane with boron on the terminal carbon, the oxidation that replaces boron by oxygen, and C-protonation of the enolate, giving 2-(4-methoxyphenyl)acetaldehyde.
- Hydrogenation of 1-methylcyclohexene to methylcyclohexaneDraw oxidative addition of H2 to palladium, migratory insertion of 1-methylcyclohexene into a Pd–H bond, and reductive elimination giving methylcyclohexane.
- HBr addition to 1-phenylcyclohexeneDraw protonation of 1-phenylcyclohexene by HBr at the ring CH carbon to the tertiary benzylic cation, then capture by bromide, giving (1-bromocyclohexyl)benzene.
- Two equivalents of HBr add to ethynylcyclohexaneDraw two successive Markovnikov additions of HBr to ethynylcyclohexane, through a vinyl cation and then a bromine-stabilised cation, giving the geminal dibromide (1,1-dibromoethyl)cyclohexane.
- Two equivalents of HBr add to hex-1-yneDraw two Markovnikov additions of HBr to hex-1-yne: protonation at C1, bromide capture at C2 to give 2-bromohex-1-ene, then the same again to give the geminal dibromide 2,2-dibromohexane.
- HBr addition to 4-methoxystyreneDraw protonation of the vinyl CH2 of 4-methoxystyrene by HBr to the benzylic cation, then capture by bromide, giving 1-(1-bromoethyl)-4-methoxybenzene.
- HBr with peroxide adds to 2-methylbut-1-eneDraw initiation (peroxide homolysis and H abstraction from HBr), then the two propagation steps: Br• adds to the CH2 carbon of 2-methylbut-1-ene and the tertiary radical takes H from HBr, giving 1-bromo-2-methylbutane.
- HBr with peroxide adds to 4-chlorostyreneDraw initiation (peroxide homolysis, then H abstraction from HBr) and the two propagation steps: Br• adds to the CH2 end of 4-chlorostyrene and the benzylic radical takes H from HBr, giving 1-(2-bromoethyl)-4-chlorobenzene.
- HBr with peroxide adds to methylenecyclopentaneDraw initiation (peroxide homolysis and H abstraction from HBr), then the two propagation steps: Br• adds to the CH2 carbon of methylenecyclopentane and the tertiary radical takes H from HBr, giving (bromomethyl)cyclopentane.
- HCl adds to 1-methylcyclopenteneDraw protonation of 1-methylcyclopentene at the ring CH to give the tertiary carbocation, then chloride capture to give 1-chloro-1-methylcyclopentane.
- HCl adds to ethylidenecyclohexane: Markovnikov chlorideDraw protonation of ethylidenecyclohexane at the exocyclic CH to give the tertiary ring carbocation, then chloride capture giving 1-chloro-1-ethylcyclohexane.
- Mercury-catalysed hydration of 4-ethynyltolueneDraw Hg2+ activation of 4-ethynyltoluene, Markovnikov attack of water at the carbon next to the ring, loss of mercury to the enol, and acid-catalysed tautomerisation to 1-(4-methylphenyl)ethan-1-one.
- Mercury-catalysed hydration of pent-1-yne to pentan-2-oneDraw Hg2+ activating pent-1-yne, water adding at C2, loss of mercury to give the enol, and acid-catalysed tautomerisation of the enol to pentan-2-one.
- 1-Phenylcyclopentene + H2SO4/H2O: Markovnikov hydrationDraw protonation of 1-phenylcyclopentene by hydronium, capture of the tertiary benzylic cation by water, and deprotonation, giving 1-phenylcyclopentan-1-ol.
- Acid-catalysed hydration of 2-methylhex-2-ene to 2-methylhexan-2-olDraw protonation of 2-methylhex-2-ene at C3, addition of water to the tertiary cation, and loss of the proton to give 2-methylhexan-2-ol.
- α-Methylstyrene + aqueous H2SO4: Markovnikov hydrationDraw protonation of α-methylstyrene by hydronium, capture of the tertiary benzylic cation by water, and deprotonation that regenerates the acid, giving 2-phenylpropan-2-ol.
- 1-Phenylcyclohexene + BH3 then H2O2: anti-Markovnikov alcoholDraw syn hydroboration of 1-phenylcyclohexene with boron on the ring CH carbon, then the oxidation steps that replace boron by OH with retention, giving trans-2-phenylcyclohexan-1-ol.
- Hydroboration–oxidation of 2-methylbut-1-eneDraw concerted syn hydroboration of 2-methylbut-1-ene with boron on the CH2 carbon, then the oxidation steps that replace boron by OH, giving the anti-Markovnikov alcohol 2-methylbutan-1-ol.
- Hydroboration–oxidation of 4-methylpent-1-eneDraw concerted syn hydroboration of 4-methylpent-1-ene with boron on the terminal CH2, then the peroxide oxidation steps that replace boron by OH, giving 4-methylpentan-1-ol.
- Hydroboration–oxidation of (E)-hex-3-eneDraw concerted syn hydroboration of (E)-hex-3-ene, then the oxidation steps that replace boron by OH with retention, giving hexan-3-ol.
- Hydroboration–oxidation of ethylidenecyclohexaneDraw concerted syn hydroboration of ethylidenecyclohexane with boron on the exocyclic CH, then the oxidation steps that replace boron by OH, giving 1-cyclohexylethan-1-ol.
- Lindlar reduction of diphenylacetylene to cis-stilbeneDraw oxidative addition of H2 to palladium, migratory insertion of diphenylacetylene into a Pd–H bond, and reductive elimination, giving (Z)-stilbene by syn addition.
- Lindlar reduction of pent-2-yne to (Z)-pent-2-eneDraw oxidative addition of H2 to palladium, migratory insertion of pent-2-yne into a Pd–H bond, and reductive elimination giving (Z)-pent-2-ene by syn addition.
- mCPBA epoxidation of 1,2-dimethylcyclopenteneDraw the one-step butterfly transfer of the outer peroxy oxygen of mCPBA to 1,2-dimethylcyclopentene, giving meso 1,2-dimethyl-6-oxabicyclo[3.1.0]hexane and 3-chlorobenzoic acid.
- Epoxidation of 1-methylcyclohexene with mCPBADraw the one-step "butterfly" transfer of the outer peroxy oxygen of mCPBA to 1-methylcyclohexene, giving 1-methylcyclohexene oxide and 3-chlorobenzoic acid.
- mCPBA epoxidation of trans-anetholeDraw the one-step butterfly transfer of the outer peroxy oxygen of mCPBA to trans-anethole, giving the trans epoxide 2-(4-methoxyphenyl)-3-methyloxirane and 3-chlorobenzoic acid.
- Methanol addition to α-methylstyrene with acidDraw protonation of α-methylstyrene by protonated methanol, capture of the tertiary benzylic cation by methanol, and deprotonation that regenerates the acid, giving (2-methoxypropan-2-yl)benzene.
- OsO4 dihydroxylation of 1,2-dimethylcyclopenteneDraw the concerted cycloaddition of OsO4 to 1,2-dimethylcyclopentene giving the cyclic osmate ester, then its hydrolysis by water to meso cis-1,2-dimethylcyclopentane-1,2-diol.
- OsO4 dihydroxylation of hex-1-ene to hexane-1,2-diolDraw the concerted cycloaddition of OsO4 to hex-1-ene giving the cyclic osmate ester, then its hydrolysis by water to hexane-1,2-diol.
- OsO4 dihydroxylation of indene to the cis diolDraw the concerted cycloaddition of OsO4 to the five-membered-ring alkene of indene and the hydrolysis of the osmate ester, giving cis-2,3-dihydro-1H-indene-1,2-diol.
- Oxymercuration of 1-methylcyclohepteneDraw oxymercuration of 1-methylcycloheptene through the mercurinium ion, water attack at the methyl-bearing carbon, deprotonation, and demercuration with NaBH4 to 1-methylcycloheptan-1-ol.
- Oxymercuration–demercuration of 4-methylstyreneDraw ionisation of mercury(II) acetate, the mercurinium ion from 4-methylstyrene, its opening by water at the benzylic carbon, deprotonation, and replacement of mercury by hydride from NaBH4, giving 1-(4-methylphenyl)ethan-1-ol.
- Ozonolysis of 1-phenylcyclohexene to 6-oxo-6-phenylhexanalDraw ozone cycloaddition to 1-phenylcyclohexene, fragmentation of the molozonide, ring closure to the ozonide, and its reduction by dimethyl sulfide, giving 6-oxo-6-phenylhexanal.
- Ozonolysis of 2-methylhex-2-ene to acetone and butanalDraw the Criegee mechanism: cycloaddition of ozone to 2-methylhex-2-ene, fragmentation of the molozonide, recombination to the ozonide, and reduction by dimethyl sulfide to acetone and butanal.
- Ozonolysis of cyclopentene to pentanedialDraw ozone adding to cyclopentene, cleavage of the molozonide, ring closure to the ozonide and its reduction by dimethyl sulfide, giving pentanedial.
- Ozonolysis of ethylidenecyclohexane to cyclohexanoneDraw ozone adding to ethylidenecyclohexane, fragmentation of the molozonide, recombination to the ozonide and its reduction by dimethyl sulfide, giving cyclohexanone and acetaldehyde.
- Hept-2-yne from propyne and 1-bromobutaneDraw deprotonation of propyne by amide ion and SN2 attack of the propynide ion on 1-bromobutane, giving hept-2-yne.
Predict the product 9
- Hydroborate a terminal alkynePredict the aldehyde formed by hydroboration–oxidation of a terminal alkyne with a bulky borane.
- Bromine and a tetrasubstituted ring alkenePredict the relative configuration of the dibromide formed by anti addition of Br₂ to 1,2-dimethylcyclohexene.
- Bromine in water and an exocyclic alkenePredict the regiochemistry of bromohydrin formation from an alkene whose two carbons differ in substitution.
- Sodium in ammonia and an internal alkynePredict the alkene geometry from a dissolving-metal reduction of an internal alkyne.
- HBr and a ring alkenePredict the Markovnikov product of HBr addition to a trisubstituted ring alkene under ionic conditions.
- Hydroboration of a tetrasubstituted ring alkeneUse syn addition and retention in the oxidation to predict the relative configuration of the alcohol from hydroboration of 1,2-dimethylcyclopentene.
- Ozonolysis of a ring alkenePredict the single ring-opened dicarbonyl product of ozonolysis of a cyclic alkene with a reductive workup.
- Ozonolysis product of indenePredict the single dialdehyde formed when the ring C=C of indene is cleaved by ozone with a reductive workup.
- Hydroboration product of 1-methylcyclohexenePredict the regio- and stereochemistry of hydroboration–oxidation on a ring alkene.
Classify 5
- Spot the anti additionClassify common alkene additions as syn or anti from their mechanisms.
- Anti dihydroxylation of an E alkeneClassify the stereoisomer formed by anti dihydroxylation of an E alkene as meso or racemic.
- Which compound forms an acetylide?Classify hydrocarbons by whether NaNH₂ can convert them into an acetylide ion.
- Which stilbene gives a meso diol with OsO4?Classify the diol from OsO4 on (Z)- and (E)-stilbene as meso or racemic, and contrast anti Br2 addition.
- Which addition is anti?Classify alkene addition reagents as syn or anti adders.
Compare 4
- Rank alkene stabilityRank alkenes by double-bond stability from heats of hydrogenation and relate the order to substitution and geometry.
- Rank carbocationsOrder methyl, primary, secondary and tertiary carbocations by stability using the number of alkyl groups on the cationic carbon.
- Rank C–H and N–H acidsOrder ethane, ethene, ammonia and ethyne by acidity and connect the ranking to the use of NaNH₂ with terminal alkynes.
- Rank para-substituted styrenes by hydration rateRank para-substituted styrenes by the rate of acid-catalysed hydration from the stability of the benzylic carbocation.
Calculate 6
- Atom economy of an mCPBA epoxidationCalculate the atom economy of epoxidising cyclohexene with mCPBA from molar masses.
- cis versus trans from heats of hydrogenationCalculate the enthalpy difference between two alkene stereoisomers from their heats of hydrogenation to the same alkane.
- Rings from formula and H₂ uptakeUse degrees of unsaturation and hydrogen uptake to count the rings in an unknown hydrocarbon.
- Stability from heats of hydrogenationCompare alkene stabilities using heats of hydrogenation.
- Rings plus π bonds in indene (C9H8)Calculate the degrees of unsaturation of indene from its formula and match them to rings and π bonds.
- Rings from formula and H2 uptakeUse the degree of unsaturation and hydrogen uptake to count rings.
Find the error 3
- Find the error in a hydration mechanismIdentify an incorrect nucleophile in a proposed mechanism for acid-catalysed alkene hydration.
- Find the error in a hydration predictionDiagnose a hydration prediction that ignores a hydride shift from a secondary to a tertiary carbocation.
- Find the error: HBr and peroxide on α-methylstyreneDiagnose a Markovnikov product predicted for a radical (peroxide) HBr addition to an aryl alkene.
Interpret the evidence 2
- Identify an alkene from its reactionsInterpret bromine, hydrogenation and ozonolysis results to identify an unknown alkene.
- Identify a C10H12 aryl alkene from H2 and O3 dataCombine the degree of unsaturation, H2 uptake and ozonolysis fragments to identify an aryl alkene.
Work backward 3
- Which alkene gave this dione?Work backwards from a single dicarbonyl ozonolysis product to a cyclic alkene by reconnecting the two carbonyl carbons with a double bond.
- Which alkene gives cyclohexanone and formaldehyde?Work backwards from ozonolysis fragments to the alkene by joining the two carbonyl carbons with a C=C.
- Alkene from its ozonolysis productsReconstruct an alkene from its reductive ozonolysis products.
Plan a synthesis 6
- Make the trans diolChoose the reagent sequence that converts a cycloalkene into the trans 1,2-diol.
- Markovnikov alcohol without rearrangementChoose the hydration method that gives the Markovnikov alcohol when the intermediate carbocation would rearrange.
- Build (Z)-hex-3-ene from acetylenePlan a sequence of two acetylide alkylations and a stereoselective reduction that converts ethyne into a Z alkene.
- Plan (E)-1-phenylbut-1-ene from phenylacetylenePlan a two-stage synthesis of a trans alkene from a terminal alkyne: acetylide alkylation, then dissolving-metal reduction.
- Reagent for a trans alkene from an alkyneChoose the reagent that reduces an internal alkyne to an E-alkene.
- Reagents for 2-phenylpropan-1-ol from α-methylstyreneChoose the reagents that hydrate α-methylstyrene anti-Markovnikov to the primary alcohol 2-phenylpropan-1-ol.
Explain why 3
- Why anti-Markovnikov?Explain why boron bonds to the less substituted alkene carbon during hydroboration.
- Why only HBr shows the peroxide effectExplain why radical anti-Markovnikov addition works with HBr but not with HCl or HI.
- Why water attacks the benzylic carbon of a bromoniumExplain the regiochemistry of bromohydrin formation from an aryl alkene through the unsymmetrical bromonium ion.
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