Organic Chemistry 1 · Reasoning about reactions
Elimination and competing pathways: practice problems
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- Force elimination at a primary carbon
- Eliminate from a defined conformer
- Continue from a carbocation
- E2 elimination — 2-bromobutane to but-2-ene
- Use the less crowded β site
- Eliminate an activated oxygen substituent
- Use the reactive cyclohexane chair
- Flip the chair before eliminating
- E1 elimination — 1-methylcyclohexene
Draw the mechanism 163
- Eliminate from a defined conformerCoordinate base attack, π-bond formation, and leaving-group departure.
- Continue from a carbocationDraw the deprotonation stage of E1 without repeating ionization.
- E2 elimination — 2-bromobutane to but-2-eneUse ethoxide to remove a β hydrogen and draw all three arrows of E2 together.
- Use the less crowded β siteConnect bulky-base regioselectivity to a terminal alkene rather than blindly choosing maximum substitution.
- Eliminate an activated oxygen substituentIdentify alkyl C–O cleavage in an alkyl sulfonate rather than breaking its S–O bond or expelling hydroxide.
- Use the reactive cyclohexane chairRecognize the trans-diaxial requirement for ring E2 and choose a β hydrogen anti to bromine.
- Flip the chair before eliminatingUse a ring flip to reach the only trans-diaxial H/Cl pair in menthyl chloride and predict the less substituted alkene.
- E1 elimination — 1-methylcyclohexeneLet chloride leave, then remove a β hydrogen to form a double bond inside the ring.
- Turn an alcohol into a ring alkeneActivate a poor leaving group and regenerate aqueous acid through the complete E1 dehydration sequence.
- Follow a carbon shift before alkene formationTrack a migrating methyl group through complete acid dehydration when the adjacent quaternary carbon has no hydride to donate.
- Remove two equivalents of hydrogen halideCarry a vicinal dihalide through a vinyl halide to an internal alkyne using two explicit strong-base equivalents.
- Create conjugation without moving the old π bondBuild a new adjacent π bond while preserving the original alkene and distinguishing elimination from allylic resonance.
- Hofmann elimination — quaternary ammonium to terminal alkeneTrack E2 of a quaternary ammonium hydroxide and explain why the departing nitrogen becomes neutral.
- E1 after a hydride shift onto a side chainFollow an E1 elimination with a hydride shift from the ring to a side-chain cation before the solvent removes a β proton.
- Dehydrate a tertiary alcohol with phosphoric acidCarry a tertiary alcohol through protonation, loss of water and β-deprotonation by dihydrogen phosphate, regenerating the H₃PO₄ catalyst.
- Choose the Zaitsev proton after ionizationDecide which of two kinds of β hydrogen an E1 base removes from a tertiary cation, and form the more substituted alkene.
- Eliminate with an amidine baseIdentify the imine nitrogen of DBU as the proton acceptor in a one-step E2 and account for the cationic amidinium product.
- A locked chair with an axial leaving groupUse a tert-butyl conformational lock to explain why cis-1-bromo-4-tert-butylcyclohexane already holds Br axial and undergoes fast E2.
- Eliminate from a tertiary bromide with a strong baseExplain why a strong base converts a tertiary alkyl bromide by E2 rather than SN2, and form the endocyclic alkene.
- Force elimination at a primary carbonExplain how a bulky alkoxide diverts a primary alkyl bromide from SN2 to E2 and draw the terminal alkene it forms.
- Explain the E alkene from an E1 dehydrationShow why E1 dehydration of butan-2-ol favors (E)-but-2-ene: the planar cation can rotate before deprotonation, so the lower-energy geometry wins.
- Dehydrate without a carbocationConvert an alcohol OH into a dichlorophosphate leaving group with POCl₃, then complete a pyridine-promoted E2 so that no carbocation ever forms.
- Predict the only alkene isomer from E2Use the single β hydrogen of (1S,2S)-1-bromo-1,2-diphenylpropane to show that anti-periplanar E2 is stereospecific and gives only one alkene stereoisomer.
- Dehydrate through a benzylic cationConnect the easy E1 dehydration of a secondary benzylic alcohol to ring delocalization of its cation, and form a conjugated alkene.
- E1cB dehydration of 4-hydroxy-4-phenylbutan-2-oneDraw the two-step E1cB dehydration: hydroxide forms the enolate at the CH2 between the ketone and the alcohol carbon, then the enolate expels hydroxide to give 4-phenylbut-3-en-2-one.
- E2 of 2-bromobutane with ethoxide (Zaitsev product)Draw the concerted E2 in which ethoxide removes a hydrogen from the internal CH2 of 2-bromobutane as bromide leaves, giving but-2-ene.
- E2 of 2-bromobutane with tert-butoxide (Hofmann product)Draw the concerted E2 in which tert-butoxide removes a methyl hydrogen of 2-bromobutane as bromide leaves, giving but-1-ene.
- Iodide converts trans-1,2-dibromocyclohexane to cyclohexeneDraw the anti elimination in which iodide attacks one bromine of trans-1,2-dibromocyclohexane while the other bromide leaves, giving cyclohexene and IBr.
- 1-Methylcyclohexene by E1 of 1-bromo-1-methylcyclohexaneDraw the two E1 steps for 1-bromo-1-methylcyclohexane in hot ethanol: ionization to the tertiary cation and loss of a ring proton to ethanol, giving 1-methylcyclohexene.
- 3-Ethylpent-2-ene from 3-bromo-3-ethylpentaneDraw the E1 of 3-bromo-3-ethylpentane in hot ethanol: ionization to the tertiary cation, then loss of a CH2 proton to ethanol giving 3-ethylpent-2-ene.
- α-Methylstyrene by E1 of 2-chloro-2-phenylpropaneDraw the E1 of 2-chloro-2-phenylpropane in hot ethanol: ionization to the tertiary benzylic cation and loss of a methyl proton to give α-methylstyrene.
- 1,1-Diphenylethene from 1,1-diphenylethanolDraw the E1 dehydration of 1,1-diphenylethanol with catalytic sulfuric acid through the diphenylmethyl-type cation to 1,1-diphenylethene.
- (E)-Stilbene from 1,2-diphenylethanolDraw the E1 dehydration of 1,2-diphenylethanol through its benzylic cation to the conjugated trans alkene, (E)-stilbene.
- 4-Methoxystyrene from 1-(4-methoxyphenyl)ethanolDraw the TsOH-catalysed E1 dehydration of 1-(4-methoxyphenyl)ethanol through its methoxy-stabilized benzylic cation to 4-methoxystyrene.
- 1-Ethylcyclohexene from 1-ethylcyclohexanolDraw the E1 dehydration of 1-ethylcyclohexanol with phosphoric acid: protonation, loss of water to the tertiary cation, and loss of a ring proton to give 1-ethylcyclohexene.
- 1-Methylcyclohexene from 1-methylcyclohexanolDraw the E1 dehydration of 1-methylcyclohexanol: protonation of OH, loss of water to the tertiary cation, and loss of a ring proton to give 1-methylcyclohexene.
- Styrene from 1-phenylethanolDraw the dehydration of 1-phenylethanol through the benzylic cation (1-phenylethyl cation) to styrene.
- (E)-1-Phenylpropene from 1-phenylpropan-2-olDraw the E1 dehydration of 1-phenylpropan-2-ol and choose the β proton that gives the conjugated alkene, (E)-1-phenylpropene.
- 2,3-Dimethylbut-2-ene from 2,3-dimethylbutan-2-olDraw the E1 dehydration of 2,3-dimethylbutan-2-ol and remove the proton that gives the tetrasubstituted Zaitsev alkene, 2,3-dimethylbut-2-ene.
- (E)-But-2-ene from butan-2-olDraw the acid-catalysed E1 dehydration of butan-2-ol: protonation, loss of water to the sec-butyl cation, and loss of a C3 proton to give (E)-but-2-ene.
- 2-Methylbut-2-ene from 2-methylbutan-2-olDraw the E1 dehydration of 2-methylbutan-2-ol, ending with loss of the C3 proton to give the trisubstituted 2-methylbut-2-ene.
- 1-Methylcyclohexene from 2-methylcyclohexanolDraw the dehydration of 2-methylcyclohexanol: protonation, loss of water, a 1,2-hydride shift to the tertiary cation, and loss of a ring proton giving 1-methylcyclohexene.
- 1-Methylcyclopentene from 2-methylcyclopentanolDraw the E1 dehydration of 2-methylcyclopentanol, including the 1,2-hydride shift to the tertiary cation, that gives 1-methylcyclopentene.
- 2-Methylpentan-2-ol dehydration to 2-methylpent-2-eneDraw the E1 dehydration of 2-methylpentan-2-ol in hot sulfuric acid through the tertiary cation to the Zaitsev alkene 2-methylpent-2-ene.
- Pentan-2-ol dehydration: (E)-pent-2-ene and other pentenesDraw the acid-catalysed E1 dehydration of pentan-2-ol to (E)-pent-2-ene and explain why (Z)-pent-2-ene and pent-1-ene form as minor alkenes.
- (E)-2-Phenylbut-2-ene from 2-phenylbutan-2-olDraw the E1 dehydration of 2-phenylbutan-2-ol through its tertiary benzylic cation to (E)-2-phenylbut-2-ene.
- α-Methylstyrene from 2-phenylpropan-2-olDraw the E1 dehydration of 2-phenylpropan-2-ol through its tertiary benzylic cation to α-methylstyrene.
- 3-Methylbutan-2-ol dehydration with a hydride shiftDraw the E1 dehydration of 3-methylbutan-2-ol in hot sulfuric acid, including the 1,2-hydride shift to the tertiary cation, ending at 2-methylbut-2-ene.
- 4-Methylcyclohexene from 4-methylcyclohexanolDraw the E1 dehydration of 4-methylcyclohexanol in hot phosphoric acid through the secondary ring cation to 4-methylcyclohexene.
- Dehydration of 4-tert-butylcyclohexanol with H3PO4Draw the phosphoric acid E1 dehydration of 4-tert-butylcyclohexanol through the secondary ring cation to 4-tert-butylcyclohexene.
- Cycloheptene from cycloheptanolDraw the three E1 steps that turn cycloheptanol into cycloheptene in hot sulfuric acid: protonation, loss of water and loss of a β proton.
- Cyclohexene from cyclohexanol with phosphoric acidDraw the phosphoric acid E1 dehydration of cyclohexanol: protonation, loss of water to the cyclohexyl cation, and deprotonation to cyclohexene.
- Cyclopentene from cyclopentanolDraw the sulfuric acid E1 dehydration of cyclopentanol: protonation, loss of water to the cyclopentyl cation, and deprotonation to cyclopentene.
- (E)-Pent-2-ene from pentan-3-olDraw the E1 dehydration of pentan-3-ol in hot sulfuric acid and show why the trans alkene, (E)-pent-2-ene, is the major product.
- 2-Methylpropene from tert-butanolDraw the three steps of the sulfuric acid dehydration of tert-butanol: protonation of OH, loss of water to the tert-butyl cation, and loss of a methyl proton to give 2-methylpropene.
- Cyclohexene and ethoxycyclohexane from bromocyclohexane in hot ethanolDraw two bromocyclohexane molecules ionizing in hot ethanol: one cation loses a proton to ethanol (E1, cyclohexene), the other is captured by ethanol and deprotonated (SN1, ethoxycyclohexane).
- 2-Methylpropene from tert-butyl bromide in hot ethanolDraw the two E1 steps for tert-butyl bromide in hot ethanol: ionization to the tert-butyl cation and loss of a methyl proton to ethanol, giving 2-methylpropene.
- Ethoxide converts 1-bromo-1-methylcyclohexane to 1-methylcyclohexeneDraw the E2 step in which ethoxide removes a ring hydrogen next to the tertiary carbon of 1-bromo-1-methylcyclohexane, giving the Zaitsev alkene 1-methylcyclohexene.
- tert-Butoxide converts 1-bromo-1-methylcyclohexane to methylenecyclohexaneDraw the E2 step in which bulky tert-butoxide removes a methyl hydrogen of 1-bromo-1-methylcyclohexane, giving the Hofmann alkene methylenecyclohexane.
- Ethoxide E2 of 1-bromo-1-methylcyclopentaneDraw the E2 step in which ethoxide removes a ring CH2 hydrogen of 1-bromo-1-methylcyclopentane, giving the trisubstituted Zaitsev alkene 1-methylcyclopentene.
- tert-Butoxide E2 of 1-bromo-1-methylcyclopentaneDraw the E2 step in which tert-butoxide removes a methyl hydrogen of 1-bromo-1-methylcyclopentane, giving the exocyclic Hofmann alkene methylenecyclopentane.
- Styrene from (1-bromoethyl)benzeneDraw the E2 of (1-bromoethyl)benzene with ethoxide that forms styrene, the alkene conjugated with the benzene ring.
- E2 of (1R,2R)-1-bromo-1,2-diphenylbutane to the Z alkeneDraw the E2 of (1R,2R)-1-bromo-1,2-diphenylbutane with ethoxide from the conformer with H and Br anti, and explain why the phenyl groups end up cis.
- Anti E2 of (1R,2R)-1-bromo-2-methyl-1-phenylbutaneDraw the anti-periplanar E2 of (1R,2R)-1-bromo-2-methyl-1-phenylbutane with ethoxide and decide that it gives (Z)-2-methyl-1-phenylbut-1-ene.
- Anti E2 of (1R,2S)-1-bromo-2-methyl-1-phenylbutaneDraw the anti-periplanar E2 of (1R,2S)-1-bromo-2-methyl-1-phenylbutane with methoxide and decide that it gives (E)-2-methyl-1-phenylbut-1-ene.
- E2 of 2-bromo-1,1-dimethylcyclohexane (one β side)Draw the E2 of 2-bromo-1,1-dimethylcyclohexane with ethoxide and explain why the only alkene is 3,3-dimethylcyclohexene.
- Ethoxide converts 2-bromo-1-phenylpropane to (E)-1-phenylpropeneDraw the E2 step in which ethoxide removes a benzylic hydrogen of 2-bromo-1-phenylpropane, giving the conjugated alkene (E)-1-phenylpropene.
- tert-Butoxide E2 of 2-bromo-2,3-dimethylbutaneDraw the E2 step in which tert-butoxide removes a methyl hydrogen of 2-bromo-2,3-dimethylbutane, giving the Hofmann alkene 2,3-dimethylbut-1-ene.
- 2,3-Dimethylbut-2-ene from 2-bromo-2,3-dimethylbutaneDraw the E2 of 2-bromo-2,3-dimethylbutane with ethoxide that removes the C3 hydrogen and forms the tetrasubstituted 2,3-dimethylbut-2-ene.
- Ethoxide E2 of 2-bromo-2,3-dimethylpentane (Zaitsev)Draw the E2 step in which ethoxide removes the tertiary C3 hydrogen of 2-bromo-2,3-dimethylpentane, giving the tetrasubstituted alkene 2,3-dimethylpent-2-ene.
- tert-Butoxide E2 of 2-bromo-2,3-dimethylpentaneDraw the E2 step in which tert-butoxide removes a methyl hydrogen of 2-bromo-2,3-dimethylpentane, giving the Hofmann alkene 2,3-dimethylpent-1-ene.
- tert-Butoxide E2 of 2-bromo-2,4,4-trimethylpentaneDraw the E2 step in which tert-butoxide removes a methyl hydrogen of 2-bromo-2,4,4-trimethylpentane, giving 2,4,4-trimethylpent-1-ene instead of the trisubstituted alkene.
- Ethoxide E2 of (2-bromopropan-2-yl)cyclohexaneDraw the E2 step in which ethoxide removes the ring CH hydrogen of (2-bromopropan-2-yl)cyclohexane, giving the tetrasubstituted alkene (propan-2-ylidene)cyclohexane.
- tert-Butoxide E2 of (2-bromopropan-2-yl)cyclohexaneDraw the E2 step in which tert-butoxide removes a methyl hydrogen of (2-bromopropan-2-yl)cyclohexane, giving the Hofmann alkene (prop-1-en-2-yl)cyclohexane.
- Ethoxide E2 of 2-bromo-2-methyl-1-phenylpropaneDraw the E2 step in which ethoxide removes a benzylic hydrogen of 2-bromo-2-methyl-1-phenylpropane, giving the conjugated alkene 2-methyl-1-phenylprop-1-ene.
- Ethoxide E2 of 2-bromo-2-methylbutane (Zaitsev)Draw the E2 step in which ethoxide removes a C3 methylene hydrogen of 2-bromo-2-methylbutane, giving the trisubstituted Zaitsev alkene 2-methylbut-2-ene.
- tert-Butoxide E2 of 2-bromo-2-methylbutane (Hofmann)Draw the E2 step in which tert-butoxide removes a methyl hydrogen of 2-bromo-2-methylbutane, giving the Hofmann alkene 2-methylbut-1-ene.
- 2-Methylhex-2-ene from 2-bromo-2-methylhexaneDraw the E2 of 2-bromo-2-methylhexane with ethoxide that removes a C3 hydrogen and gives the Zaitsev alkene 2-methylhex-2-ene.
- 2-Methylhex-1-ene from 2-bromo-2-methylhexaneDraw the E2 of 2-bromo-2-methylhexane with tert-butoxide that removes a methyl hydrogen and gives the Hofmann alkene 2-methylhex-1-ene.
- Ethoxide E2 of 2-bromo-3-ethylpentane (Zaitsev)Draw the E2 step in which ethoxide removes the tertiary C3 hydrogen of 2-bromo-3-ethylpentane, giving the trisubstituted Zaitsev alkene 3-ethylpent-2-ene.
- 3-Ethylpent-1-ene from 2-bromo-3-ethylpentaneDraw the E2 of 2-bromo-3-ethylpentane with tert-butoxide that removes a methyl hydrogen and gives the Hofmann alkene 3-ethylpent-1-ene.
- tert-Butoxide converts (2-bromoethyl)benzene to styreneDraw the E2 step in which tert-butoxide removes a benzylic hydrogen of (2-bromoethyl)benzene while bromide leaves, giving styrene.
- Ethoxide E2 of 2-bromopentane to (E)-pent-2-eneDraw the E2 step in which ethoxide removes a C3 hydrogen of 2-bromopentane anti to bromine, giving the Zaitsev alkene (E)-pent-2-ene.
- tert-Butoxide E2 of 2-bromopentane to pent-1-eneDraw the E2 step in which bulky tert-butoxide removes a C1 methyl hydrogen of 2-bromopentane, giving the Hofmann alkene pent-1-ene.
- Ethoxide converts 2-chloro-3-methylbutane to 2-methylbut-2-eneDraw the E2 step in which ethoxide removes the tertiary hydrogen of 2-chloro-3-methylbutane, giving the trisubstituted alkene 2-methylbut-2-ene.
- Anti E2 of (2R,3R)-2-bromo-3,4-dimethylpentaneDraw the anti-periplanar E2 of (2R,3R)-2-bromo-3,4-dimethylpentane with ethoxide and decide that it gives (E)-3,4-dimethylpent-2-ene.
- (E)-3-Phenylpent-2-ene from (2R,3R)-2-bromo-3-phenylpentaneDraw the anti-periplanar E2 of (2R,3R)-2-bromo-3-phenylpentane with ethoxide and decide that it gives (E)-3-phenylpent-2-ene.
- (E)-2-Phenylpent-2-ene from (2R,3R)-3-bromo-2-phenylpentaneDraw the anti-periplanar E2 of (2R,3R)-3-bromo-2-phenylpentane with ethoxide and decide that it gives (E)-2-phenylpent-2-ene.
- (Z)-3-Methylhex-2-ene from (2R,3S)-2-bromo-3-methylhexaneDraw the anti-periplanar E2 of (2R,3S)-2-bromo-3-methylhexane with methoxide and decide that it gives (Z)-3-methylhex-2-ene.
- (Z)-2-Phenylbut-2-ene from (2R,3S)-2-bromo-3-phenylbutaneDraw the anti-periplanar E2 of (2R,3S)-2-bromo-3-phenylbutane with hydroxide and decide that it gives (Z)-2-phenylbut-2-ene.
- E2 of (2R,3S)-2-bromo-3-phenylpentane to the Z alkeneDraw the anti-periplanar E2 of (2R,3S)-2-bromo-3-phenylpentane with methoxide and use the reacting conformer to show why (Z)-3-phenylpent-2-ene forms.
- Anti E2 of (2R,3S)-3-phenylbutan-2-yl tosylateDraw the anti-periplanar E2 of (2R,3S)-3-phenylbutan-2-yl tosylate with ethoxide and decide that it gives (Z)-2-phenylbut-2-ene.
- (Z)-2-Phenylpent-2-ene from (2S,3R)-3-bromo-2-phenylpentaneDraw the anti-periplanar E2 of (2S,3R)-3-bromo-2-phenylpentane with methoxide and decide that it gives (Z)-2-phenylpent-2-ene.
- Ethoxide E2 of 3-bromo-2,2-dimethylbutaneDraw the E2 step in which ethoxide removes a C4 methyl hydrogen of 3-bromo-2,2-dimethylbutane, giving 3,3-dimethylbut-1-ene because the quaternary carbon has no hydrogen.
- 2,3-Dimethylpent-2-ene from 3-bromo-2,3-dimethylpentaneDraw the E2 of 3-bromo-2,3-dimethylpentane with ethoxide that removes the tertiary C2 hydrogen and gives tetrasubstituted 2,3-dimethylpent-2-ene.
- 2-Ethyl-3-methylbut-1-ene from 3-bromo-2,3-dimethylpentaneDraw the E2 of 3-bromo-2,3-dimethylpentane with tert-butoxide that removes a hydrogen of the C3 methyl and gives 2-ethyl-3-methylbut-1-ene.
- 2,4-Dimethylpent-2-ene from 3-bromo-2,4-dimethylpentaneDraw the E2 of 3-bromo-2,4-dimethylpentane with ethoxide that removes a tertiary β-hydrogen and gives 2,4-dimethylpent-2-ene.
- Ethoxide E2 of 3-bromo-2-methylpentane (Zaitsev)Draw the E2 step in which ethoxide removes the tertiary C2 hydrogen of 3-bromo-2-methylpentane, giving the trisubstituted Zaitsev alkene 2-methylpent-2-ene.
- tert-Butoxide E2 of 3-bromo-2-methylpentaneDraw the E2 step in which tert-butoxide removes a C4 methylene hydrogen of 3-bromo-2-methylpentane, giving (E)-4-methylpent-2-ene rather than the trisubstituted alkene.
- tert-Butoxide E2 of 3-bromo-3-methylpentaneDraw the E2 step in which tert-butoxide removes a hydrogen from the methyl branch of 3-bromo-3-methylpentane, giving the Hofmann alkene 2-ethylbut-1-ene.
- Ethoxide converts 3-bromo-3-methylpentane to 3-methylpent-2-eneDraw the E2 step in which ethoxide removes a hydrogen from an ethyl CH2 of 3-bromo-3-methylpentane, giving the trisubstituted alkene 3-methylpent-2-ene.
- tert-Butoxide converts 3-bromocyclohexene to cyclohexa-1,3-dieneDraw the E2 step in which tert-butoxide removes a hydrogen from the CH2 next to the C–Br carbon of 3-bromocyclohexene, giving the conjugated cyclohexa-1,3-diene.
- Ethoxide E2 of 3-bromopentane to (E)-pent-2-eneDraw the E2 step in which ethoxide removes a C4 hydrogen of 3-bromopentane from the conformer with the two alkyl groups anti, giving (E)-pent-2-ene.
- tert-Butoxide E2 of 3-methylbutan-2-yl tosylateDraw the E2 step in which tert-butoxide removes a C1 methyl hydrogen of 3-methylbutan-2-yl tosylate as tosylate leaves, giving 3-methylbut-1-ene.
- Anti E2 of (3R,4R)-3-bromo-3,4-dimethylhexaneDraw the anti-periplanar E2 of (3R,4R)-3-bromo-3,4-dimethylhexane with ethoxide and decide that it gives (E)-3,4-dimethylhex-3-ene.
- (E)-3-Methylhept-3-ene from (3R,4R)-4-bromo-3-methylheptaneDraw the anti-periplanar E2 of (3R,4R)-4-bromo-3-methylheptane with ethoxide and decide that it gives (E)-3-methylhept-3-ene.
- Anti E2 of (3R,4S)-3-bromo-3,4-dimethylhexaneDraw the anti-periplanar E2 of (3R,4S)-3-bromo-3,4-dimethylhexane with methoxide and decide that it gives (Z)-3,4-dimethylhex-3-ene.
- (Z)-3-Methylhex-3-ene from (3R,4S)-3-bromo-4-methylhexaneDraw the anti-periplanar E2 of (3R,4S)-3-bromo-4-methylhexane with methoxide and decide that it gives (Z)-3-methylhex-3-ene.
- (E)-Hept-3-ene from 4-bromoheptaneDraw the E2 of 4-bromoheptane with ethoxide through the conformer that gives (E)-hept-3-ene.
- tert-Butoxide E2 of 4-methylpentan-2-yl tosylateDraw the E2 step in which tert-butoxide removes a C1 methyl hydrogen of 4-methylpentan-2-yl tosylate, giving the terminal alkene 4-methylpent-1-ene.
- Ethoxide converts bromocyclopentane to cyclopenteneDraw the E2 step in which ethoxide removes a ring hydrogen next to the C–Br carbon of bromocyclopentane, giving cyclopentene.
- Methylenecyclohexane from (bromomethyl)cyclohexaneDraw the E2 reaction of (bromomethyl)cyclohexane with potassium tert-butoxide and explain why elimination beats SN2 at this primary carbon.
- E2 of chlorocyclohexane with methoxideDraw the E2 of chlorocyclohexane with hot methoxide from the minor chair with chlorine axial, giving cyclohexene.
- E2 of cis-1,2-dibromocyclohexane to 1-bromocyclohexeneDraw the E2 of cis-1,2-dibromocyclohexane with one equivalent of ethoxide, removing the hydrogen anti to the axial bromine to give the vinyl bromide 1-bromocyclohexene.
- E2 of (1S,2R)-1-bromo-1,2-dimethylcyclohexaneDraw the trans-diaxial E2 of (1S,2R)-1-bromo-1,2-dimethylcyclohexane, bromine cis to the 2-methyl, with ethoxide to give 1,2-dimethylcyclohexene.
- Ethoxide converts cis-1-bromo-2-methylcyclohexane to 1-methylcyclohexeneDraw the trans-diaxial E2 step in which ethoxide removes the axial hydrogen on the methyl-bearing carbon of cis-1-bromo-2-methylcyclohexane, giving 1-methylcyclohexene.
- E2 of cis-1-bromo-4-methylcyclohexane with ethoxideDraw the E2 of cis-1-bromo-4-methylcyclohexane with ethoxide from its favoured chair, where bromine is already axial, to give 4-methylcyclohexene.
- E2 of cis-1-bromo-4-tert-butyl-1-methylcyclohexaneDraw the E2 of cis-1-bromo-4-tert-butyl-1-methylcyclohexane with ethoxide in its locked chair, with bromine axial, to give 4-tert-butyl-1-methylcyclohexene.
- E2 of cis-1-chloro-2-isopropylcyclohexane (Zaitsev)Draw the trans-diaxial E2 of cis-1-chloro-2-isopropylcyclohexane with ethoxide, removing the axial hydrogen on the isopropyl-bearing carbon to give 1-isopropylcyclohexene.
- E2 of cis-2-methylcyclohexyl tosylate (Zaitsev)Draw the trans-diaxial E2 of cis-2-methylcyclohexyl tosylate with ethoxide, removing the axial hydrogen on the methyl-bearing carbon as tosylate leaves.
- Ethoxide converts cis-1-tert-butyl-4-chlorocyclohexane to 4-tert-butylcyclohexeneDraw the E2 step in which ethoxide removes an axial hydrogen anti to the locked axial chlorine of cis-1-tert-butyl-4-chlorocyclohexane, giving 4-tert-butylcyclohexene.
- E2 of cis-4-tert-butylcyclohexyl tosylate with tert-butoxideDraw the E2 of cis-4-tert-butylcyclohexyl tosylate with potassium tert-butoxide from the locked chair with an axial tosylate, giving 4-tert-butylcyclohexene.
- Cyclohexene from cyclohexyl tosylateDraw the E2 of cyclohexyl tosylate with tert-butoxide, with the tosylate anion leaving as cyclohexene forms.
- DBU converts butan-2-yl tosylate to (E)-but-2-eneDraw the E2 step in which the amidine nitrogen of DBU removes an internal β hydrogen of butan-2-yl tosylate while tosylate leaves, giving (E)-but-2-ene.
- 2-Methylpropene from 2-methylpropan-1-olDraw the protonation of 2-methylpropan-1-ol and the concerted E2 that removes the C2 hydrogen as water leaves, giving 2-methylpropene.
- Ethene from ethanol at 180 °CDraw the protonation of ethanol by sulfuric acid and the E2 in which hydrogen sulfate removes a methyl proton as water leaves, giving ethene.
- 2-Methylpropene from 2-bromo-2-methylpropane and hydroxideDraw the one-step E2 of 2-bromo-2-methylpropane with hydroxide: removal of a methyl proton, C=C formation and loss of bromide to give 2-methylpropene.
- Hydroxide converts meso-2,3-dibromobutane to (E)-2-bromobut-2-eneDraw the anti-periplanar E2 step that removes one hydrogen and one bromide from meso-2,3-dibromobutane, and use the anti geometry to predict (E)-2-bromobut-2-ene.
- 2-Methylpent-2-ene from 2-bromo-2-methylpentaneDraw the one-step E2 of 2-bromo-2-methylpentane with ethoxide that gives the Zaitsev alkene 2-methylpent-2-ene.
- Ethoxide converts 2-bromobutane to (E)-but-2-eneDraw the E2 step in which ethoxide removes a hydrogen from the internal CH2 of 2-bromobutane, giving the Zaitsev alkene (E)-but-2-ene.
- Ethoxide converts 2-bromohexane to (E)-hex-2-eneDraw the E2 step in which ethoxide removes a C3 hydrogen of 2-bromohexane, giving the Zaitsev alkene (E)-hex-2-ene.
- Ethoxide converts bromocyclohexane to cyclohexeneDraw the E2 step in which ethoxide removes an axial hydrogen anti to the axial bromine of bromocyclohexane, giving cyclohexene.
- Ethoxide converts tert-butyl bromide to 2-methylpropeneDraw the E2 step in which ethoxide removes a methyl hydrogen from tert-butyl bromide while bromide leaves, giving 2-methylpropene.
- Oct-1-ene from octan-2-yl tosylateDraw the E2 of octan-2-yl tosylate with tert-butoxide that removes a C1 methyl hydrogen and expels tosylate to give oct-1-ene.
- tert-Butoxide E2 of pentan-2-yl tosylate to pent-1-eneDraw the E2 step in which tert-butoxide removes a C1 methyl hydrogen of pentan-2-yl tosylate while the tosylate anion leaves, giving pent-1-ene.
- (Z)-2-Bromobut-2-ene from (±)-2,3-dibromobutaneDraw the anti-periplanar E2 of (2S,3S)-2,3-dibromobutane with one equivalent of hydroxide and deduce that it gives (Z)-2-bromobut-2-ene.
- tert-Butoxide converts 1-bromobutane to but-1-eneDraw the concerted E2 step in which tert-butoxide removes a hydrogen from C2 of 1-bromobutane while bromide leaves from C1, giving but-1-ene.
- tert-Butoxide converts 1-chlorohexane to hex-1-eneDraw the concerted E2 step in which tert-butoxide removes a hydrogen from C2 of 1-chlorohexane while chloride leaves from C1, giving hex-1-ene.
- tert-Butoxide converts 1-iodo-2-methylpropane to 2-methylpropeneDraw the E2 step in which tert-butoxide removes the tertiary β hydrogen of 1-iodo-2-methylpropane while iodide leaves, giving 2-methylpropene.
- tert-Butoxide converts 2-bromobutane to but-1-eneDraw the E2 step in which bulky tert-butoxide removes a terminal methyl hydrogen of 2-bromobutane, giving the Hofmann alkene but-1-ene.
- tert-Butoxide converts 2-bromohexane to hex-1-eneDraw the E2 step in which bulky tert-butoxide removes a methyl hydrogen of 2-bromohexane, giving the Hofmann alkene hex-1-ene.
- Propene from 2-iodopropaneDraw the concerted E2 in which tert-butoxide removes a methyl hydrogen of 2-iodopropane and iodide leaves to give propene.
- 2-Methylpropene from tert-butyl bromide and cyanideDraw the E2 reaction of tert-butyl bromide with sodium cyanide in DMSO and explain why cyanide acts as a base here instead of a nucleophile.
- E2 of (1R,2R)-1-bromo-1,2-dimethylcyclohexaneDraw the E2 of (1R,2R)-1-bromo-1,2-dimethylcyclohexane, bromine trans to the 2-methyl, with ethoxide and explain why 1,6-dimethylcyclohexene forms.
- E2 of trans-1-bromo-3-methylcyclohexane with ethoxideDraw the E2 of trans-1-bromo-3-methylcyclohexane with ethoxide from the chair with bromine axial, removing the axial C2 hydrogen to give 3-methylcyclohexene.
- E2 of trans-1-bromo-4-methylcyclohexane after a ring flipDraw the E2 of trans-1-bromo-4-methylcyclohexane with methoxide from the minor diaxial chair and explain why it reacts more slowly than the cis isomer.
- E2 of trans-1-bromo-4-tert-butyl-1-methylcyclohexaneDraw the E2 of trans-1-bromo-4-tert-butyl-1-methylcyclohexane with ethoxide, where equatorial bromine forces loss of a methyl hydrogen to give the exocyclic alkene.
- E2 of trans-1-chloro-2-isopropylcyclohexane via ring flipDraw the E2 of trans-1-chloro-2-isopropylcyclohexane with ethoxide from the chair with chlorine axial, and explain why 3-isopropylcyclohexene forms instead of the Zaitsev alkene.
- E2 of trans-2-methylcyclohexyl tosylate (anti-Zaitsev)Draw the E2 of trans-2-methylcyclohexyl tosylate with ethoxide from the diaxial chair and explain why 3-methylcyclohexene, not 1-methylcyclohexene, forms.
- tert-Butoxide converts trans-1,2-dibromocyclohexane to 3-bromocyclohexeneDraw the trans-diaxial E2 step in which tert-butoxide removes the axial hydrogen on the CH2 carbon next to one C–Br of trans-1,2-dibromocyclohexane, giving 3-bromocyclohexene.
- (E)-Oct-2-ene from 2-bromooctane and ethoxideDraw the E2 of 2-bromooctane with sodium ethoxide at 55 °C that gives (E)-oct-2-ene, and explain why it beats SN2 for this secondary bromide.
- 1-Methylcyclohexene from 1-methylcyclohexanol with POCl3Draw the POCl3/pyridine dehydration of 1-methylcyclohexanol: O-phosphorylation, deprotonation, and the pyridine E2 that removes an anti ring hydrogen.
- 2-Methylbut-2-ene from 2-methylbutan-2-ol with POCl3Draw the POCl3/pyridine dehydration of 2-methylbutan-2-ol: phosphorylation, deprotonation and the pyridine E2 that gives 2-methylbut-2-ene.
- Cyclohexene from cyclohexanol with POCl3 and pyridineDraw cyclohexanol attacking POCl3, pyridine removing the O–H proton, and the pyridine-promoted E2 in which the dichlorophosphate leaves to give cyclohexene (POCl3 route).
- p-Menth-2-ene from menthol with POCl3 and pyridineDraw the POCl3/pyridine dehydration of menthol: phosphorylation, deprotonation, and the anti-periplanar E2 that gives p-menth-2-ene rather than the Zaitsev alkene.
- SN1 and E1 of 2-bromo-2-methylbutane in ethanolDraw two 2-bromo-2-methylbutane molecules ionizing in ethanol: one tertiary cation loses a proton (E1, 2-methylbut-2-ene), the other is captured by ethanol and deprotonated (SN1, 2-ethoxy-2-methylbutane).
- 2-Chloro-2,3-dimethylbutane in hot ethanol: SN1 and E1Draw two 2-chloro-2,3-dimethylbutane molecules ionizing in hot ethanol: one tertiary cation loses its tertiary β proton (E1, 2,3-dimethylbut-2-ene), the other is trapped by ethanol (SN1, 2-ethoxy-2,3-dimethylbutane).
- tert-Butyl alcohol and 2-methylpropene from tert-butyl chloride in waterDraw two tert-butyl chloride molecules ionizing in hot water: one cation is captured by water (SN1, tert-butyl alcohol), the other loses a proton to water (E1, 2-methylpropene).
- Isopropyl acetate from 2-bromopropane and acetateDraw the SN2 reaction of 2-bromopropane with sodium acetate in DMF and explain why a weakly basic nucleophile substitutes a secondary bromide instead of eliminating.
- Benzyl tert-butyl ether from benzyl bromide and KOtBuDraw the one-step SN2 attack of tert-butoxide on benzyl bromide and explain why this bulky base cannot eliminate here.
- Ethyl isobutyl sulfide from isobutyl bromide by SN2Draw the SN2 attack of ethanethiolate on the β-branched primary bromide isobutyl bromide and say why E2 stays minor.
- (S)-2-(Ethylsulfanyl)butane from (R)-2-bromobutaneDraw the backside SN2 attack of ethanethiolate on (R)-2-bromobutane and assign the inverted configuration of the thioether product.
- 1-Methoxybutane from 1-bromobutane and methoxideDraw the SN2 reaction of 1-bromobutane with sodium methoxide in methanol and explain why it beats E2 for this primary bromide.
Predict the product 4
- Choose the accessible β siteApply a specified base-size effect to alkene regioselectivity.
- Read a stereospecific eliminationMap a defined anti conformer to alkene relative geometry.
- E2 product of meso-2,3-dibromobutaneUse the anti-periplanar requirement to predict E/Z geometry from a specific diastereomer.
- Major alkene from 2-fluoropentane and methoxidePredict how a poor fluoride leaving group shifts E2 regiochemistry toward the terminal alkene.
Classify 2
- Classify a base-driven pathwayCombine substrate hindrance and reagent basicity without invoking forbidden SN2.
- Secondary bromide with ethoxidePredict the main pathway for a secondary alkyl halide with a strong, unhindered base.
Compare 6
- Compare rearrangement possibilitiesUse a skeleton change to distinguish stepwise cation chemistry from simple E2.
- Rank four C5 alkenes by stabilityRank isomeric alkenes by degree of substitution and E/Z geometry.
- Rank alcohols by dehydration rateRelate acid-catalysed dehydration rates to carbocation stability.
- Rank 2-halohexanes by percent hex-1-eneOrder halide leaving groups by how much terminal alkene their E2 reactions give.
- Which gives more but-1-ene: ammonium salt or bromide?Compare the alkene ratio from a trimethylammonium leaving group with that from a bromide in E2.
- Which isomer gives 1-methylcyclohexene?Apply the trans-diaxial requirement to predict E2 regiochemistry in substituted cyclohexanes.
Calculate 7
- Percent Zaitsev alkene from a 0.8 kcal/mol gapTurn a small barrier difference into the percentage of the major alkene.
- Zaitsev:Hofmann ratio from a 1.4 kcal/mol barrier gapConvert a difference in activation free energies into a kinetic product ratio.
- Count E2 alkenes from 2-bromo-2-methylbutaneCount the distinct alkenes an E2 reaction can give by inventorying β-hydrogens.
- Count E2 alkenes from 3-bromo-2-methylpentaneCount E2 products including E/Z stereoisomers for a substrate with two different β-carbons.
- Predict the E2 rate constant of a β-deuterated bromideUse a measured kH/kD to predict how much slower the deuterated substrate eliminates.
- Calculate kH/kD for E2 of 2-bromopropaneCalculate a primary kinetic isotope effect from two E2 rate constants and relate it to C–H cleavage.
- Percent Zaitsev product from GC peak areasCalculate the percentage of the Zaitsev alkene from gas chromatography peak areas.
Find the error 2
- Find the absent elimination hydrogenUse a molecular diagram to reject E2 when the β carbon has no hydrogen.
- Why neomenthyl chloride eliminates faster than menthylExplain an E2 rate difference between diastereomers from the population of the reactive chair.
Interpret the evidence 5
- Use trans-diaxial availabilityPrioritize cyclohexane conformation over the more-substituted-alkene rule.
- Read a base-size table for 2-bromo-2-methylbutaneDraw the correct conclusion from data relating alkoxide size to the amount of terminal alkene.
- Read the rate lawUse kinetic data to tell E2 from E1.
- What a kH/kD of 1.1 says about the mechanismInterpret a small kinetic isotope effect as evidence that no C–H bond breaks in the rate-determining step.
- Reactive chair of trans-1-bromo-2-methylcyclohexanePick the chair conformer that can undergo E2 and predict the alkene it gives.
Work backward 2
- Pick the diastereomer that gives (Z)-2-phenylbut-2-eneWork backward from an alkene geometry to the diastereomer that gives it by anti E2.
- Pick the bromide that gives only pent-2-eneChoose an alkyl halide whose every β hydrogen leads to the target internal alkene.
Plan a synthesis 3
- Plan a conjugated elimination productSelect the β site that creates conjugation while retaining existing unsaturation.
- Pick the base for the Hofmann alkeneChoose a bulky base to favour the less substituted E2 alkene.
- Plan 2,3-dimethylbut-2-ene by E2Choose a substrate and base that give a tetrasubstituted alkene as the major E2 product.
Explain why 3
- Assess evidence from replacing β HConnect a primary isotope effect to bond cleavage without overstating proof.
- Why heat favours eliminationExplain the temperature dependence of substitution versus elimination with ΔG = ΔH − TΔS.
- Why heating lowers the Zaitsev:Hofmann ratioExplain why a fixed barrier difference gives lower selectivity at higher temperature.
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