Organic Chemistry 2 · Functional-group transformations
Conjugation and cycloaddition: practice problems
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- (E)-1-Bromobut-2-ene from buta-1,3-diene at 40 °C
- Connect delocalization to bond formation
- Diels–Alder reaction — butadiene and ethene bond map
- Choose the adjacent diene-addition branch
- Follow solvent capture of a conjugated cation
- Protonate a delocalized carbon anion
- Thia-Michael addition — thiolate addition and workup
- Diels–Alder reaction — an alkyne dienophile
- Diels–Alder reaction — cyclopentadiene to a bridged bicycle
Draw the mechanism 64
- Connect delocalization to bond formationTrace the specified 1,4-addition pathway through an allylic intermediate while distinguishing resonance from a reaction.
- Diels–Alder reaction — butadiene and ethene bond mapDraw all three electron-pair movements in a Diels–Alder reaction.
- Choose the adjacent diene-addition branchTrace full 1,2 addition and identify which original diene double bond survives.
- Follow solvent capture of a conjugated cationComplete 1,4 hydration with a neutral nucleophile and regenerate the acid instead of stopping at oxonium.
- Protonate a delocalized carbon anionUse two-arrow anion resonance before proton capture and avoid confusing a negative charge with an empty orbital.
- Thia-Michael addition — thiolate addition and workupConnect beta sulfur addition, enolate resonance, and alpha protonation in a complete Michael-type addition.
- Diels–Alder reaction — an alkyne dienophileUse one of the alkyne π pairs to close a six-membered ring with two double bonds.
- Diels–Alder reaction — cyclopentadiene to a bridged bicycleMap a cyclic diene into a bridged bicyclic skeleton rather than treating its bridge as a substituent to discard.
- Diels–Alder reaction — dimethyl maleate stereochemistryCombine three-arrow Diels–Alder electron flow with explicit same-face ester substituents in the product.
- Retro-Diels–Alder reaction — norbornene bond mapIdentify the two sigma bonds broken in a retro-Diels–Alder event while retaining the original five-membered diene ring.
- Intramolecular Diels–Alder reaction — fused-ring closureCount a three-carbon tether through intramolecular Diels–Alder formation of fused five- and six-membered rings.
- Trap an unsymmetrical allylic donor at carbonUse donor resonance to form a branched carbonyl-addition product rather than protonating the delocalized carbon anion.
- Oct-2-en-1-yl anion: initiation of butadiene polymerization by butyllithiumDraw the butyl carbanion adding to C1 of buta-1,3-diene to give an allylic anion and its resonance contributor with the charge on the terminal carbon, the chain end that adds the next monomer.
- Methyl 3-(benzylamino)propanoate by aza-Michael additionDraw the conjugate addition of benzylamine to methyl acrylate and the methanol-relayed proton transfers that give the secondary amine mono-adduct.
- 4-(Diethylamino)butan-2-one by aza-Michael addition to MVKDraw the conjugate addition of diethylamine to methyl vinyl ketone and the two proton transfers through methanol that give the neutral β-amino ketone.
- (E)-1,4-Dibromobut-2-ene from buta-1,3-dieneDraw bromine adding to C1 of buta-1,3-diene to give an allylic cation, its resonance contributor with the charge on C4, and capture by bromide at C4 to give (E)-1,4-dibromobut-2-ene.
- Br2 1,4-addition to 2,3-dimethylbuta-1,3-dieneDraw bromine adding to a CH2 of 2,3-dimethylbuta-1,3-diene, the allylic contributor with the charge on the far CH2, and bromide capture there to give 1,4-dibromo-2,3-dimethylbut-2-ene.
- Cl2 1,2-addition to (E)-penta-1,3-dieneDraw chlorine adding to the terminal CH2 of (E)-penta-1,3-diene to give the methyl-substituted allylic cation, then chloride capture at C2 to give the kinetic 1,2-adduct (E)-4,5-dichloropent-2-ene.
- 3-Oxocyclohexane-1-carbonitrile by conjugate addition of cyanideDraw cyanide adding to the β-carbon of cyclohex-2-en-1-one, the enolate contributor with charge on the α-carbon, and protonation by ammonium to give 3-oxocyclohexane-1-carbonitrile.
- Diels–Alder of anthracene and N-methylmaleimide at C9/C10Draw the concerted Diels–Alder reaction of anthracene across C9 and C10 with N-methylmaleimide and explain why the central ring, not an outer ring, acts as the diene.
- Diels–Alder of buta-1,3-diene and acrylonitrileDraw the concerted Diels–Alder reaction of buta-1,3-diene with acrylonitrile to give cyclohex-3-ene-1-carbonitrile, tracking which bonds form and where the new C=C ends up.
- cis-4a,5,8,8a-Tetrahydronaphthalene-1,4-dione from benzoquinoneDraw the Diels–Alder reaction of buta-1,3-diene with one C=C of p-benzoquinone and show the cis ring fusion of the bicyclic enedione.
- Diels–Alder of butadiene and (E)-crotonaldehydeDraw the concerted Diels–Alder reaction of buta-1,3-diene with (E)-crotonaldehyde and explain why the methyl and formyl groups end up trans on the cyclohexene ring.
- Dimethyl trans-cyclohex-4-ene-1,2-dicarboxylate from dimethyl fumarateDraw the concerted Diels–Alder reaction of buta-1,3-diene with dimethyl fumarate and show that the trans dienophile gives the trans diester.
- cis-1,2,3,6-Tetrahydrophthalic anhydride by Diels–AlderDraw the concerted Diels–Alder reaction of buta-1,3-diene (s-cis) with maleic anhydride and show that the cis dienophile gives the cis-fused anhydride.
- Endo Diels–Alder of cyclohexa-1,3-diene and maleic anhydrideDraw the concerted Diels–Alder reaction of cyclohexa-1,3-diene with maleic anhydride and explain why the anhydride ends up endo in the bicyclo[2.2.2]octene product.
- Diels–Alder of cyclopentadiene and DMAD: a norbornadieneDraw the concerted Diels–Alder reaction of cyclopenta-1,3-diene with dimethyl acetylenedicarboxylate and see why the alkyne leaves a second C=C in the bridged norbornadiene diester.
- Ethyl endo-bicyclo[2.2.1]hept-5-ene-2-carboxylate by Diels–AlderDraw the concerted Diels–Alder reaction of cyclopenta-1,3-diene with ethyl acrylate and explain why the ester ends up endo in the bridged product.
- Endo Diels–Alder of cyclopentadiene and methyl vinyl ketoneDraw the concerted Diels–Alder reaction of cyclopenta-1,3-diene with methyl vinyl ketone and explain why the acetyl group ends up endo in 2-acetylnorbornene.
- Endo Diels–Alder of cyclopentadiene and N-phenylmaleimideDraw the concerted Diels–Alder reaction of cyclopenta-1,3-diene with N-phenylmaleimide and explain why the imide ring ends up endo, on the face toward the new C=C.
- 3,4-Dimethylcyclohex-3-ene-1-carbaldehyde by Diels–AlderDraw the concerted Diels–Alder reaction of 2,3-dimethylbuta-1,3-diene with acrolein to give 3,4-dimethylcyclohex-3-ene-1-carbaldehyde.
- Oxanorbornadiene diester from furan and DMAD by Diels–AlderDraw the concerted Diels–Alder reaction of furan with dimethyl acetylenedicarboxylate that builds the oxygen-bridged bicyclic diene.
- exo-7-Oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic anhydride from furanDraw the Diels–Alder reaction of furan with maleic anhydride and explain why the exo oxanorbornene adduct is the one isolated.
- Diels–Alder of (2E,4E)-hexa-2,4-diene and maleic anhydrideDraw the concerted Diels–Alder reaction of (2E,4E)-hexa-2,4-diene with maleic anhydride and explain why both methyls and both anhydride carbons end up all cis in the product.
- Diels–Alder of 2-methoxybutadiene and methyl vinyl ketoneDraw the concerted Diels–Alder reaction of 2-methoxybuta-1,3-diene with methyl vinyl ketone and explain why the acetyl group ends up para (1,4) to the methoxy-bearing alkene carbon.
- Diels–Alder of 1-methoxybutadiene and methyl acrylateDraw the concerted Diels–Alder reaction of (E)-1-methoxybuta-1,3-diene with methyl acrylate and explain the ortho regiochemistry and the endo, cis relationship of OMe and CO2Me.
- Diels–Alder of (E)-penta-1,3-diene and acroleinDraw the concerted Diels–Alder reaction of (E)-penta-1,3-diene with acrolein and explain the ortho regiochemistry and the endo, cis relationship of the methyl and the formyl group.
- Cyclopenta-1,3-diene by cracking dicyclopentadieneDraw the retro-Diels–Alder that splits dicyclopentadiene into two molecules of cyclopenta-1,3-diene.
- 3,3-Dimethylcyclohexanone by Me2CuLi conjugate additionDraw the 1,4-addition of lithium dimethylcuprate to the trisubstituted β carbon of 3-methylcyclohex-2-en-1-one and the carbon protonation of the enolate that gives a quaternary carbon.
- 4-Phenylpentan-2-one by Ph2CuLi 1,4-addition to pentenoneDraw the conjugate (1,4) addition of lithium diphenylcuprate to (E)-pent-3-en-2-one and the carbon protonation of the lithium enolate in the NH4Cl workup.
- (E)-2-Phenylpent-3-en-2-ol from PhMgBr and pentenoneDraw the direct (1,2) addition of phenylmagnesium bromide to the carbonyl carbon of (E)-pent-3-en-2-one and the protonation of the alkoxide in the NH4Cl workup.
- HBr addition to (E)-1-phenylbutadiene: styrene keptDraw protonation of (E)-1-phenylbuta-1,3-diene at the terminal CH2 and bromide capture at C3 of the allylic, benzylic cation, giving (E)-(3-bromobut-1-en-1-yl)benzene with the alkene still conjugated to the ring.
- 3-Bromobut-1-ene from buta-1,3-diene at −80 °CDraw protonation of buta-1,3-diene at C1 and capture of the allylic cation by bromide at C2, the kinetic 1,2-addition product 3-bromobut-1-ene.
- (E)-1-Bromobut-2-ene from buta-1,3-diene at 40 °CDraw protonation of buta-1,3-diene, the allylic resonance contributor with the charge on C4, and capture by bromide at C4 to give the thermodynamic 1,4-adduct (E)-1-bromobut-2-ene.
- HBr 1,4-addition to 2,3-dimethylbuta-1,3-diene at 40 °CDraw protonation of 2,3-dimethylbuta-1,3-diene at a CH2, the allylic contributor with the charge on the far CH2, and bromide capture there to give the thermodynamic 1,4-adduct 1-bromo-2,3-dimethylbut-2-ene.
- HBr 1,2-addition to isoprene: 3-bromo-3-methylbut-1-eneDraw protonation of isoprene at the CH2 of the methyl-bearing alkene and capture of the tertiary allylic cation by bromide at the tertiary carbon, the kinetic 1,2-adduct 3-bromo-3-methylbut-1-ene.
- 1-Bromo-3-methylbut-2-ene (prenyl bromide) from isopreneDraw protonation of isoprene at the CH2 of the methyl-bearing alkene to give a tertiary allylic cation, its primary contributor, and capture by bromide at the CH2 end to give prenyl bromide.
- HBr addition to (E)-penta-1,3-diene: (E)-4-bromopent-2-eneDraw protonation of (E)-penta-1,3-diene at C1, the resonance contributor of the pent-3-en-2-yl cation, and bromide capture at the far end, and see why 1,2- and 1,4-addition give the same (E)-4-bromopent-2-ene.
- HCl addition to cyclohexa-1,3-diene: 3-chlorocyclohexeneDraw protonation of cyclohexa-1,3-diene at C1 to give the symmetric cyclohexenyl allylic cation and chloride capture to give 3-chlorocyclohex-1-ene.
- 3-Chlorocyclopent-1-ene from cyclopenta-1,3-dieneDraw protonation of cyclopenta-1,3-diene at a terminal diene carbon, the resonance contributor of the allylic cation, and capture by chloride to give 3-chlorocyclopent-1-ene.
- Bromohydrin from buta-1,3-diene: 1-bromobut-3-en-2-olDraw bromine adding to C1 of buta-1,3-diene, water attacking the allylic C2, and water removing the oxonium proton to give the bromohydrin 1-bromobut-3-en-2-ol.
- 3-Bromobut-1-ene isomerizes to (E)-1-bromobut-2-eneDraw ionization of 3-bromobut-1-ene to the allylic cation, its contributor with the charge on the terminal carbon, and recapture of bromide there to give (E)-1-bromobut-2-ene.
- Isoprene anionic polymerization: sec-BuLi initiationDraw sec-butyllithium adding to C1 of isoprene, then the resonance contributor of the allylic anion with the charge on C4, the chain end that adds the next isoprene.
- Isoprene cationic polymerization: initiation and propagationDraw protonation of isoprene by the BF3–water complex, the resonance contributor of the dimethylallyl cation, and its attack on a second isoprene that gives the next tertiary allylic cation.
- Diethyl 2-(2-cyanoethyl)malonate by Michael additionDraw the ethoxide-catalysed Michael addition of diethyl malonate to acrylonitrile: enolate formation, attack at the β carbon and protonation of the nitrile-stabilized carbanion.
- (E)-1-Bromobut-2-ene by NBS bromination of but-1-eneDraw Br–Br homolysis, abstraction of an allylic hydrogen of but-1-ene, the resonance contributor of the allylic radical, and bromine transfer at the CH2 end to give (E)-1-bromobut-2-ene.
- 3-Bromocyclohex-1-ene by allylic bromination with NBSDraw initiation by Br–Br homolysis, abstraction of an allylic hydrogen of cyclohexene by Br•, and bromine transfer from Br2 to the allylic radical to give 3-bromocyclohex-1-ene.
- 1-(Bromomethyl)cyclohexene from methylenecyclohexane and NBSDraw the NBS radical chain on methylenecyclohexane: Br–Br homolysis, abstraction of a ring allylic hydrogen, the radical resonance contributor on the exocyclic CH2, and bromine transfer there.
- Allyl anion from propene and butyllithiumDraw butyllithium removing an allylic C–H proton from propene and the resonance contributor of the allyl anion.
- Buta-1,3-diene and ethene by retro-Diels–Alder of cyclohexeneDraw the concerted retro-Diels–Alder fragmentation of cyclohexene into buta-1,3-diene and ethene.
- But-3-en-2-ol by SN1 hydrolysis of crotyl chlorideDraw the ionization of (E)-crotyl chloride in aqueous acetone, the secondary contributor of the allylic cation, capture by water at that carbon and the deprotonation that gives the alcohol.
- 3-Ethoxy-3-methylbut-1-ene by SN1 of prenyl chlorideDraw the ionization of prenyl chloride in ethanol, the resonance contributor of the dimethylallyl cation, capture by ethanol at the tertiary carbon and the final deprotonation.
- (E)-1-Methoxybut-2-ene by SN2′ substitutionDraw the concerted SN2′ reaction in which methoxide bonds to the terminal alkene carbon of 3-chlorobut-1-ene, the C=C shifts, and chloride leaves from C3.
- Methyl (E)-4-bromobut-2-enoate by Wohl–Ziegler brominationDraw the radical chain that brominates the γ-methyl group of methyl (E)-crotonate with NBS: Br• formation, allylic hydrogen abstraction and bromine transfer from Br2.
Predict the product 15
- Diels–Alder reaction — retain cis dienophile geometryPredict relative stereochemistry transferred through a stereospecific cycloaddition.
- 1,4-Adduct of Br2 with buta-1,3-dienePick the 1,4-addition product of one equivalent of bromine with buta-1,3-diene from candidate dibromides.
- Diels–Alder Adduct of Butadiene and DMADPredict the cyclohexa-1,4-diene formed when an alkyne acts as the dienophile.
- Maleate vs Fumarate Diels–Alder StereochemistryPredict the relative stereochemistry of the adducts from cis and trans dienophiles.
- Bicyclic Product from CyclopentadieneIdentify the bridged bicyclic skeleton formed when a cyclic diene undergoes a Diels–Alder reaction.
- (E,E)-Hexa-2,4-diene Diels–Alder Methyl GeometryPredict how diene substituent geometry is transferred to the cyclohexene product.
- Diels–Alder product of butadiene and maleic anhydridePredict the cycloadduct of buta-1,3-diene and maleic anhydride, including the cis ring fusion retained from the dienophile.
- Diels–Alder regiochemistry: isoprene and methyl acrylatePredict the major regioisomer from the Diels–Alder reaction of isoprene with methyl acrylate using the "para" rule for 2-substituted dienes.
- 1-Methoxybutadiene + Acrolein RegiochemistryApply the "ortho" rule for a 1-substituted electron-rich diene.
- Isoprene + Methyl Acrylate RegiochemistryApply the "para" rule for a 2-substituted diene.
- Conjugate Addition of Cyanide to CyclohexenonePredict the 1,4-adduct of cyanide with a cyclic enone (structure choice).
- Products of HBr with buta-1,3-dienePredict the 1,2- and 1,4-addition products of HBr with buta-1,3-diene.
- Major HBr adduct of buta-1,3-diene at 40 °CPredict which HBr adduct of buta-1,3-diene dominates when the addition runs under thermodynamic control at 40 °C.
- Major product at −80 °CPredict which HBr adduct of butadiene dominates under kinetic control.
- Repeat Unit of 1,4-PolybutadienePredict the repeat unit formed by 1,4-polymerization of a conjugated diene.
Classify 6
- Recognize a continuous p systemClassify a diene by connectivity rather than the number of double bonds alone.
- Spot the conjugated dieneClassify dienes as conjugated, isolated or cumulated from their structures.
- What Does Endo Mean in a Diels–Alder Adduct?Define the endo orientation of a dienophile substituent in a Diels–Alder adduct.
- Which Reagents Add 1,4 to an Enone?Classify nucleophiles as 1,2- or 1,4-adders to α,β-unsaturated ketones.
- Double-Bond Geometry of Natural RubberClassify natural rubber by monomer, linkage and C=C geometry.
- Which conformer reacts in a Diels–Alder?Distinguish the more stable diene conformer from the one that undergoes Diels–Alder.
Compare 4
- Read a matched hydrogenation comparisonInfer relative reactant stability from a qualitative matched-product heat comparison.
- Rank Dienes for the Diels–Alder ReactionRank dienes by Diels–Alder reactivity from s-cis access and donor substituents.
- Rank Dienophiles for the Diels–Alder ReactionRank dienophiles by Diels–Alder reactivity from their electron-withdrawing groups.
- Rank diene stabilityRank cumulated, isolated and conjugated dienes by thermodynamic stability.
Calculate 4
- Calculate an equilibrated mixtureTranslate a supplied equilibrium constant into product fractions.
- New σ Bonds in Butadiene + EthyleneDo the σ/π bond bookkeeping for a Diels–Alder cycloaddition.
- Electrons in the Diels–Alder Cyclic Transition StateCount the π electrons that reorganize in a [4+2] cycloaddition.
- Conjugation energy from heats of hydrogenationCalculate the conjugation energy of buta-1,3-diene from heats of hydrogenation.
Find the error 1
- Diels–Alder stereochemistry — endo/exo vs cis/transDiagnose confusion between endo preference and cis/trans retention.
Interpret the evidence 4
- Use barrier informationIdentify the kinetic product from explicitly supplied activation barriers.
- Resonance partner of the allyl cationIdentify the second resonance contributor of the allyl cation.
- HOMO of buta-1,3-dieneIdentify the HOMO of buta-1,3-diene and its number of nodes.
- Energy diagram: kinetic vs thermodynamic HBr adductUse transition-state and product energies on a reaction-energy diagram to name the kinetic and the thermodynamic product of HBr addition to buta-1,3-diene.
Work backward 3
- Retro-Diels–Alder reaction — disconnect the cyclohexene ringIdentify the fragments of a retro-Diels–Alder disconnection.
- Disconnect Norborn-5-ene-2-carbonitrileRecognize a bridged bicyclic alkene as a cyclopentadiene Diels–Alder adduct.
- Disconnect 4-Methylcyclohexene (Retro-Diels–Alder)Identify the diene and dienophile that would build a substituted cyclohexene.
Explain why 6
- Diels–Alder requirements — the s-cis conformational gateDistinguish s-cis geometry from E/Z alkene stereochemistry.
- Why allyl bromide ionizes fastExplain the high SN1 reactivity of allylic halides.
- Why an Enone's β-Carbon Is ElectrophilicExplain with resonance why nucleophiles add to the β-carbon of an α,β-unsaturated ketone.
- Why Cyclopentadiene Is Sold as Its DimerExplain why dicyclopentadiene must be cracked before cyclopentadiene is used as a diene.
- Why 1,2-addition of HBr to butadiene is fasterExplain why bromide captures C2 of the but-2-enyl cation faster than C4 during HBr addition to buta-1,3-diene.
- Why conjugated dienes are more stableExplain the two sources of extra stability in conjugated dienes.
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