Organic Chemistry 1 · Exam review
Radicals, alcohols and ethers: practice problems
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- 1-Chloropropane from propan-1-ol and SOCl2
- Radical chlorination of cyclohexane
- Selective photobromination of 2,3-dimethylbutane
- Radical chain addition of HBr to styrene
- Anti-Markovnikov addition of HBr to 2-methylpropene with a peroxide
- SN1 conversion of 2-methylbutan-2-ol to 2-chloro-2-methylbutane
- PBr₃ converts 2-methylpropan-1-ol to 1-bromo-2-methylpropane
- Butan-1-ol to pentanenitrile through the tosylate
- HBr cleaves anisole to phenol and bromomethane
Draw the mechanism 60
- Radical chlorination of cyclohexaneDraw the initiation and both propagation steps of the light-driven chlorination of cyclohexane with fishhook arrows, and explain why only one monochloride forms.
- Selective photobromination of 2,3-dimethylbutaneDraw the light-initiated radical bromination of 2,3-dimethylbutane with fishhook arrows and explain why bromine replaces a tertiary hydrogen.
- Radical chain addition of HBr to styreneDraw the two propagation steps of peroxide-initiated HBr addition to styrene with fishhook arrows: bromine-atom addition to the CH₂ end and hydrogen transfer from HBr to the benzylic radical.
- Anti-Markovnikov addition of HBr to 2-methylpropene with a peroxideDraw the radical chain in which a peroxide initiator makes Br•, Br• adds to the CH₂ end of 2-methylpropene, and the tertiary radical takes H from HBr to give 1-bromo-2-methylpropane.
- SN1 conversion of 2-methylbutan-2-ol to 2-chloro-2-methylbutaneDraw the SN1 conversion of 2-methylbutan-2-ol into 2-chloro-2-methylbutane in concentrated hydrochloric acid: protonation, loss of water and capture of the tertiary cation by chloride.
- PBr₃ converts 2-methylpropan-1-ol to 1-bromo-2-methylpropaneDraw how PBr₃ turns the OH of 2-methylpropan-1-ol into a leaving group and how bromide displaces it by SN2 without rearrangement.
- Butan-1-ol to pentanenitrile through the tosylateDraw the tosylation of butan-1-ol with TsCl and pyridine, then the SN2 displacement of tosylate by cyanide that gives pentanenitrile.
- HBr cleaves anisole to phenol and bromomethaneDraw the protonation of anisole by HBr and the SN2 attack of bromide on the methyl carbon that gives phenol and bromomethane, and explain why the aryl C–O bond survives.
- Intramolecular Williamson synthesis of oxolane from 4-chlorobutan-1-olDraw the deprotonation of 4-chlorobutan-1-ol by hydroxide and the intramolecular SN2 that closes the five-membered ring of oxolane.
- Williamson synthesis of methoxycyclohexaneDraw the deprotonation of cyclohexanol by sodium hydride and the SN2 attack of the cyclohexoxide ion on iodomethane that gives methoxycyclohexane.
- Acid-catalysed methanolysis of 2,2-dimethyloxirane at the tertiary carbonDraw the acid-catalysed opening of 2,2-dimethyloxirane in methanol: protonation by CH₃OH₂⁺, attack of methanol at the tertiary carbon and deprotonation that gives 2-methoxy-2-methylpropan-1-ol.
- Methoxide opens 2,2-dimethyloxirane at the CH₂ carbonDraw the SN2 opening of 2,2-dimethyloxirane by methoxide at the less hindered carbon and the proton transfer from methanol that gives 1-methoxy-2-methylpropan-2-ol.
- 2-Bromo-2-methylhexane by radical brominationDraw the radical chain that converts 2-methylhexane into 2-bromo-2-methylhexane with Br2 and light, and explain the selectivity of the bromine atom.
- 2-Bromo-2-methylpentane by radical brominationDraw the initiation and both propagation steps of the light-driven bromination of 2-methylpentane with fishhook arrows, and explain why the tertiary hydrogen is replaced.
- Racemic 1-(1-bromoethyl)-4-methylbenzene from 4-ethyltolueneDraw the radical chain that brominates the secondary benzylic position of 4-ethyltoluene with Br2 and light, and explain why the product is racemic.
- 1-Bromo-1-ethylcyclopentane by radical brominationDraw the initiation and both propagation steps that turn ethylcyclopentane into 1-bromo-1-ethylcyclopentane with Br2 and light.
- Benzylic bromination of isobutylbenzene with Br2 and lightDraw the radical chain that brominates isobutylbenzene with Br2 and light, and explain why the benzylic hydrogen is replaced rather than the tertiary one.
- Racemic bromination of (S)-1-chloro-2-methylbutaneDraw the bromination of (S)-1-chloro-2-methylbutane at its stereocentre with Br2 and light, and explain why the 2-bromo-1-chloro-2-methylbutane formed is racemic.
- Chlorination of 2,2-dimethylbutane: three monochloridesDraw the three hydrogen abstractions in the chlorination of 2,2-dimethylbutane with Cl2 and light, and calculate the percentage of each monochloride.
- 1-Chloro-1-methylcyclopentane by radical chlorinationDraw the chain that converts methylcyclopentane into 1-chloro-1-methylcyclopentane with fishhook arrows, and explain why chlorination gives a mixture.
- 1-Chloro-2,2-dimethylpropane from neopentaneDraw the light-driven chlorination of neopentane with fishhook arrows and explain why it gives a single monochloride.
- Chlorination of pentane: three monochloropentanesDraw the chlorination of pentane at C1, C2 and C3 with Cl2 and light, and predict the ratio of 1-chloropentane, 2-chloropentane and 3-chloropentane.
- 1-Bromo-2,3-dimethylbut-2-ene by NBS allylic brominationDraw the radical chain that converts 2,3-dimethylbut-2-ene into 1-bromo-2,3-dimethylbut-2-ene with NBS and light.
- Allylic bromination of but-1-ene: two allylic bromidesDraw the NBS bromination of but-1-ene with light, including the resonance of the allylic radical, to explain why 3-bromobut-1-ene and (E)-1-bromobut-2-ene both form.
- 3-Bromocycloheptene by allylic bromination with NBSDraw the radical chain that converts cycloheptene into 3-bromocycloheptene with NBS and light, using fishhook arrows.
- 3-Bromocyclopentene by allylic brominationDraw the radical chain that converts cyclopentene into 3-bromocyclopentene with NBS and light, using fishhook arrows.
- 1-Bromo-1-methylcyclohexane from 1-methylcyclohexanol and HBrDraw the SN1 conversion of 1-methylcyclohexan-1-ol into 1-bromo-1-methylcyclohexane with HBr.
- Racemic 2-chloro-2-phenylbutane from (S)-2-phenylbutan-2-olDraw the SN1 conversion of (S)-2-phenylbutan-2-ol into 2-chloro-2-phenylbutane with concentrated HCl, and explain why the product is racemic.
- Mesylation of (S)-4-phenylbutan-2-ol with MsCl and Et3NDraw the mesylation of (S)-4-phenylbutan-2-ol with MsCl and Et3N, and explain why the stereocentre keeps its configuration.
- Bromocyclohexane from cyclohexanol and PBr3Draw how PBr3 converts the OH of cyclohexanol into a leaving group and how bromide then displaces it (cyclohexanol).
- (S)-2-Bromo-4-methylpentane from (R)-4-methylpentan-2-olDraw how PBr3 activates the OH of (R)-4-methylpentan-2-ol and how bromide displaces it with inversion to give (S)-2-bromo-4-methylpentane.
- (S)-(4-Bromobutan-2-yl)benzene from (S)-3-phenylbutan-1-olDraw the PBr3 conversion of (S)-3-phenylbutan-1-ol into (S)-(4-bromobutan-2-yl)benzene and decide what happens to the stereocentre.
- PBr3 on trans-2-methylcyclohexanol: the cis bromideDraw the PBr3 conversion of trans-2-methylcyclohexanol into cis-1-bromo-2-methylcyclohexane and explain why the ring relationship changes from trans to cis.
- 1-Chloropropane from propan-1-ol and SOCl2Draw the formation of the alkyl chlorosulfite from propan-1-ol and SOCl2 and its SN2 displacement by chloride that gives 1-chloropropane.
- (R)-3-Chloroheptane from (S)-heptan-3-ol with SOCl2Draw the conversion of (S)-heptan-3-ol into (R)-3-chloroheptane with SOCl2 and pyridine, showing where the configuration at C3 is inverted.
- Cyanide SN2 on cis-4-methylcyclohexyl tosylateDraw cyanide displacing the tosylate of cis-4-methylcyclohexyl tosylate, and explain why trans-4-methylcyclohexane-1-carbonitrile is formed.
- (R)-2-Ethylpentanenitrile from (S)-hexan-3-yl tosylateDraw the SN2 displacement of the tosylate in (S)-hexan-3-yl tosylate by cyanide and assign the configuration of the 2-ethylpentanenitrile formed.
- (S)-2-Iodoheptane from (R)-heptan-2-yl tosylate and NaIDraw the SN2 reaction of (R)-heptan-2-yl tosylate with sodium iodide in acetone and assign the configuration of the 2-iodoheptane.
- Azidocyclopentane from cyclopentanol via its tosylateDraw the tosylation of cyclopentanol and the SN2 displacement of the tosylate by azide that gives azidocyclopentane.
- Tosylation of (R)-5-methylhexan-2-ol with retentionDraw the tosylation of (R)-5-methylhexan-2-ol with TsCl and pyridine, and explain why C2 keeps its configuration.
- Ethoxycyclohexane by alkoxymercuration of cyclohexeneDraw the alkoxymercuration of cyclohexene in ethanol and the NaBH4 demercuration that gives ethoxycyclohexane.
- 1,4-Dibromobutane from oxolane and excess HBrDraw both acid-promoted SN2 cleavages that turn oxolane (THF) into 1,4-dibromobutane with excess HBr.
- Phenol and iodoethane from ethoxybenzene and HIDraw the acidic cleavage of ethoxybenzene by HI and show which C–O bond breaks.
- tert-Butyl methyl ether from tert-butanol and methanolDraw the acid-catalysed SN1 formation of tert-butyl methyl ether from tert-butanol in methanol.
- Benzyl isopropyl ether by Williamson synthesisDraw the deprotonation of propan-2-ol by NaH and the SN2 attack of the alkoxide on benzyl bromide.
- 1-Aminopropan-2-ol from 2-methyloxirane and ammoniaDraw the SN2 opening of 2-methyloxirane by ammonia at the CH₂ carbon and the proton transfers that give 1-aminopropan-2-ol.
- trans-2-Azidocyclohexan-1-ol from cyclohexene oxideDraw the anti opening of cyclohexene oxide by azide and the protonation that gives trans-2-azidocyclohexan-1-ol.
- 2,2-Dimethyloxirane from a bromohydrinDraw the deprotonation of 1-bromo-2-methylpropan-2-ol and the intramolecular SN2 that closes 2,2-dimethyloxirane.
- 3-Hydroxypentanenitrile from 2-ethyloxirane and cyanideDraw cyanide opening 2-ethyloxirane at its CH2 carbon and the workup protonation that gives 3-hydroxypentanenitrile.
- trans-2-Hydroxycyclohexane-1-carbonitrile by epoxide openingDraw the anti opening of cyclohexene oxide by cyanide and the workup that gives trans-2-hydroxycyclohexane-1-carbonitrile.
- 2-Cyclohexylethan-1-ol from cyclohexylmagnesium bromideDraw cyclohexylmagnesium bromide opening oxirane and the acidic workup that gives 2-cyclohexylethan-1-ol.
- 1-(Ethylthio)-2-methylpropan-2-ol from 2,2-dimethyloxiraneDraw ethanethiolate opening 2,2-dimethyloxirane at the CH2 carbon and the proton transfer that gives 1-(ethylthio)-2-methylpropan-2-ol.
- 1-Bromopropan-2-ol from 2-methyloxirane and HBrDraw the protonation of 2-methyloxirane by HBr and the opening by bromide that gives 1-bromopropan-2-ol.
- 3-(Methylthio)butan-2-ol from meso cis-2,3-dimethyloxiraneDraw methanethiolate opening meso cis-2,3-dimethyloxirane with inversion and explain why 3-(methylthio)butan-2-ol forms as a racemate.
- (S)-1-(Methylthio)propan-2-ol from (S)-2-methyloxiraneDraw methanethiolate opening (S)-2-methyloxirane at the CH2 carbon and show why (S)-1-(methylthio)propan-2-ol keeps the configuration.
- 1-Phenylpropan-1-ol from styrene oxide and MeMgBrDraw methylmagnesium bromide opening styrene oxide at the CH2 carbon and the workup that gives 1-phenylpropan-1-ol.
- 1-Phenylpropan-2-ol from 2-methyloxirane and PhMgBrDraw phenylmagnesium bromide opening 2-methyloxirane at the CH2 carbon and the workup that gives 1-phenylpropan-2-ol.
- 2-Methoxy-2-phenylethan-1-ol from styrene oxide in acidic methanolDraw the acid-catalysed opening of 2-phenyloxirane by methanol at the benzylic carbon.
- trans-2-(Phenylthio)cyclohexan-1-ol from cyclohexene oxideDraw the anti opening of cyclohexene oxide by thiophenoxide and the proton transfer from ethanol that gives trans-2-(phenylthio)cyclohexan-1-ol.
- 1-Phenyl-2-(phenylthio)ethan-1-ol from styrene oxideDraw thiophenoxide opening styrene oxide at the CH2 carbon and the proton transfer from ethanol that gives 1-phenyl-2-(phenylthio)ethan-1-ol.
Predict the product 14
- Major product of brominating 2-methylbutanePredict the major monobromide from radical bromination of a branched alkane.
- Neopentyl alcohol with HBrPredict the rearranged product formed when a neopentyl alcohol reacts with HBr.
- Stereochemistry of a tosylate–bromide sequenceTrack configuration through tosylation (retention) and SN2 displacement (inversion) of a chiral secondary alcohol.
- Cleaving methoxycyclohexane with one equivalent of HIPredict which C–O bond of a methyl secondary-alkyl ether breaks with one equivalent of HI.
- Configuration after azide opens (R)-2-methyloxiranePredict regiochemistry and configuration when a nucleophile opens a chiral terminal epoxide at the carbon that is not a stereocentre.
- Stereochemistry of opening a cis-epoxideDeduce the stereoisomers formed by anti opening of a meso epoxide with hydroxide.
- Grignard reagent opens an epoxidePredict the alcohol formed when a Grignard reagent opens an unsymmetrical epoxide.
- LiAlH₄ opens 1-methylcyclohexene oxidePredict the alcohol formed when hydride opens an unsymmetrical epoxide.
- Acidic methanolysis of 1-methylcyclohexene oxidePredict the regiochemistry of acid-catalysed epoxide opening by a weak nucleophile on a trisubstituted epoxide.
- Methoxide opens 2-methyloxiranePredict the regiochemistry of base-promoted opening of an unsymmetrical epoxide by an alkoxide.
- Major product of 3-methylbutan-2-ol with HBrPredict the rearranged bromide formed when a secondary alcohol next to a tertiary C–H reacts with HBr by SN1.
- Tosylate then azide on (R)-butan-2-olTrack configuration through tosylation (retention) and SN2 displacement (inversion).
- Where methanethiolate opens 1-methylcyclohexene oxidePredict the site and stereochemistry of thiolate opening of 1-methylcyclohexene oxide under basic conditions.
- Where methanol opens a protonated epoxidePredict the regiochemistry of acid-catalysed epoxide opening at a tertiary carbon.
Classify 2
- How does a tert-butyl ether cleave?Classify the pathway by which HBr cleaves an ether that has a tertiary alkyl group.
- Which hydrogen does a bromine radical remove?Identify the hydrogen a selective bromine radical abstracts from a branched alkane.
Compare 5
- Rank carbon radicals by stabilityRank methyl, primary, secondary, tertiary and allylic radicals by stability from C–H bond dissociation energies.
- Rank alcohols in the Lucas testRank primary, secondary and tertiary alcohols by their rate of SN1 reaction with HCl and ZnCl₂.
- Rank Williamson electrophilesRank alkyl bromides by how well they give an ether with sodium ethoxide by SN2.
- Rank leaving groups from hydroxide to triflateRank hydroxide, halides and sulfonates by leaving-group ability to explain why an alcohol OH must be activated.
- Which route inverts (R)-octan-2-ol to the (S)-acetate?Count the bond-breaking events at the stereocenter to decide retention or inversion across reagent sequences.
Calculate 6
- Selectivity of bromine for a tertiary hydrogenCalculate the percentage of tertiary bromide from photobromination of 2-methylpropane using relative reactivity factors.
- Enthalpy of hydrogen abstraction by Br•Use bond dissociation energies to calculate the enthalpy change of a radical hydrogen-abstraction step.
- Product ratio in the chlorination of propaneCombine hydrogen counts with relative reactivity to predict the percentage of the secondary chloride from propane chlorination.
- How many monochlorides does 3-methylpentane give?Count the constitutional monochlorination products of 3-methylpentane by grouping equivalent hydrogens.
- Tertiary chloride share from chlorinating 2-methylpentaneCombine hydrogen counts with per-hydrogen reactivity to predict a radical chlorination product ratio.
- Tertiary chloride share from 2,2,3-trimethylbutanePredict the tertiary chloride percentage when 2,2,3-trimethylbutane is chlorinated, from hydrogen counts and per-hydrogen rates.
Find the error 2
- Find the error in an HBr mechanismIdentify the flaw in a proposed SN1 mechanism for a primary alcohol reacting with HBr.
- What goes wrong with methoxide and tert-butyl bromide?Diagnose why a Williamson plan with a tertiary alkyl halide gives elimination, and choose the working disconnection for tert-butyl methyl ether.
Interpret the evidence 1
- Why HCl gives an optically inactive benzylic chlorideInterpret the loss of optical rotation when a chiral tertiary benzylic alcohol is converted to its chloride with HCl.
Work backward 3
- Which alcohol gives (R)-2-bromopentane with PBr₃?Work backwards through a PBr₃ substitution to the configuration of the starting alcohol.
- Disconnect ethoxybenzeneChoose the Williamson disconnection for an aryl alkyl ether.
- Best Williamson precursors for ethoxycyclohexaneChoose the alkoxide and alkyl halide pair that makes ethoxycyclohexane by SN2 rather than elimination.
Plan a synthesis 4
- Make a chloride with inversionChoose the reagent that converts a chiral secondary alcohol into the chloride with clean inversion.
- Choose a precursor for oxaneChoose the halo-alcohol whose intramolecular Williamson reaction gives a six-membered cyclic ether.
- Plan a Williamson synthesis of tert-butyl methyl etherChoose the alkoxide/halide pair that lets a Williamson ether synthesis proceed by SN2 rather than E2.
- Plan butan-1-ol from bromoethane through an epoxidePlan a two-carbon chain extension from an alkyl halide to a primary alcohol with a Grignard reagent and oxirane.
Explain why 7
- Why bromination is more selective than chlorinationExplain the different selectivities of chlorination and bromination with the Hammond postulate.
- Why the peroxide effect works only for HBrExplain from the energetics of both propagation steps why peroxides reverse the regiochemistry of HBr addition but not of HCl or HI addition.
- Why an OH group must be activatedExplain why an alcohol's OH must be protonated or converted into a sulfonate or phosphite ester before substitution.
- NaH or NaOH for a Williamson synthesis?Use pKa values to explain why sodium hydride, not sodium hydroxide, is used to form an alkoxide from a simple alcohol.
- Why epoxides open but ethers do notExplain why epoxides react with strong nucleophiles under basic conditions while ordinary ethers do not.
- Benzylic opening of styrene oxide in acidExplain how acid-catalysed epoxide opening can occur at the more substituted carbon yet still with inversion.
- Why NBS brominates cyclohexene at the allylic carbonExplain how the low Br2 concentration from NBS lets allylic radical substitution beat electrophilic addition to cyclohexene.
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