Organic Chemistry 2 · Aromatic systems
Electrophilic aromatic substitution: practice problems
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- Isopropylbenzene (cumene) from benzene and 1-chloropropane
- Benzenesulfonic acid from benzene in hot sulfuric acid
- Nitronium encounter and proton transfer
- Friedel–Crafts acylation — acylium capture
- Electrophilic aromatic substitution — bromination of anisole
- A sulfur electrophile and a proton relay
- Remove a reversible aromatic blocking group
- Friedel–Crafts alkylation — propene activation and ring capture
- Friedel–Crafts alkylation — rearranging alcohol donor
Draw the mechanism 98
- Nitronium encounter and proton transferExecute ring attack with coupled nitronium π-bond opening and rearomatization.
- Friedel–Crafts acylation — acylium captureForm a bond to the acylium carbon without giving it more than eight electrons, then restore aromaticity.
- Electrophilic aromatic substitution — bromination of anisoleUse Br₂ to replace a ring hydrogen with bromine, then restore the aromatic ring.
- A sulfur electrophile and a proton relayComplete SO₃ sulfonation through a zwitterionic arenium ion and solvent-mediated proton transfers.
- Remove a reversible aromatic blocking groupReverse aromatic sulfonation by ipso protonation, C–S cleavage and explicit hydration of the sulfur fragment.
- Friedel–Crafts alkylation — propene activation and ring captureGenerate the carbon electrophile by alkene protonation and regenerate the acid during aromatic alkylation.
- Friedel–Crafts alkylation — rearranging alcohol donorLink alcohol activation, water loss and hydride migration to a rearranged aromatic C–C bond.
- Join two aromatic fragments through nitrogenUse a diazonium electrophile in aromatic substitution while preserving both nitrogens rather than expelling N₂.
- Intramolecular Friedel–Crafts alkylation — indane ring closureMap an intramolecular Friedel–Crafts alkylation into a five-membered fused ring while conserving the terminal alkene carbon.
- Electrophilic aromatic substitution — nitrationMake NO₂⁺ from nitric acid, add it to benzene, and regenerate sulfuric acid.
- Brominate an arene with a Lewis-acid catalystFollow Br₂ activation by FeBr₃, σ-complex formation and its contributors, and catalyst regeneration during aromatic bromination.
- Friedel–Crafts acetylation of anisoleDraw the formation of the acylium ion from acetyl chloride and AlCl3, its attack by the para carbon of anisole with the methoxy-stabilised arenium ion, and the deprotonation that gives 4-methoxyacetophenone.
- Friedel–Crafts ethylation of benzene with ethene and HCl/AlCl3Draw how HCl and AlCl3 turn ethene into an ethyl electrophile, how benzene attacks it, and how tetrachloroaluminate restores the aromatic ring to give ethylbenzene.
- SNAr: hydroxide displaces chloride from 1-chloro-2,4-dinitrobenzeneDraw the addition of hydroxide to 1-chloro-2,4-dinitrobenzene to form the Meisenheimer complex, the loss of chloride, and the acid–base steps that give 2,4-dinitrophenol after acidification.
- 2-Acetylpyrrole from pyrrole and acetic anhydrideDraw addition of pyrrole C2 to a carbonyl of acetic anhydride, loss of acetate from the tetrahedral intermediate and rearomatisation to 2-acetylpyrrole without any Lewis acid.
- 4-Nitrobenzyl bromide via NBS and benzoyl peroxideDraw homolysis of dibenzoyl peroxide, loss of CO2 to a phenyl radical, its reaction with Br2, and the chain steps that turn the methyl group of 4-nitrotoluene into CH2Br.
- Blanc chloromethylation of benzeneDraw attack of benzene on protonated formaldehyde, rearomatisation to benzyl alcohol, and its SN1 conversion to benzyl chloride.
- Bromination of 2-naphthol to 1-bromo-2-naphtholDraw C1 bromination of 2-naphthol, showing the oxonium contributor and why the benzo ring stays aromatic only for C1 attack.
- Bromination of 4-nitrotoluene to 2-bromo-4-nitrotolueneDraw bromination of 4-nitrotoluene ortho to the methyl group, moving the arenium charge onto the methyl-bearing carbon and never onto the nitro-bearing carbon.
- Ring bromination of acetophenone to 3-bromoacetophenoneDraw AlCl₃ complexation of the acetophenone carbonyl, meta attack of the complexed ring on bromine, and release of 3-bromoacetophenone.
- 2,4,6-Tribromoaniline from aniline in bromine waterDraw the three successive brominations of aniline in water (para, then both ortho positions) that give 2,4,6-tribromoaniline.
- Bromination of furan to 2-bromofuranDraw C2 attack of furan on bromine without a Lewis acid, oxygen stabilisation of the cation and loss of the C2 proton to 2-bromofuran.
- Bromination of indole with NBS to 3-bromoindoleDraw C3 attack of indole on the bromine of NBS, the iminium-stabilised cation and deprotonation by succinimide anion to 3-bromoindole.
- Bromination of N,N-dimethylaniline at the para carbonDraw para bromination of N,N-dimethylaniline without a Lewis acid, showing the iminium contributor that the nitrogen lone pair provides.
- 1-Bromonaphthalene from naphthalene and Br₂Draw bromination of naphthalene at C1, using the arenium contributors to explain why C1 beats C2.
- Bromination of nitrobenzene to 3-bromonitrobenzeneDraw meta bromination of nitrobenzene and walk the arenium charge over all three ring positions, none of them the nitro-bearing carbon.
- Bromination of p-xylene to 2-bromo-1,4-dimethylbenzeneDraw monobromination of p-xylene, placing the arenium charge first on the methyl-bearing carbon and then para to the new C–Br bond.
- Bromination of pyridine to 3-bromopyridineDraw C3 attack of pyridine on bromine, the carbon-only delocalisation of the cation and deprotonation to 3-bromopyridine.
- 2-bromotoluene from toluene with Br₂ and FeBr₃Draw bromination of toluene at the ortho position, showing the arenium contributor with the charge on the methyl-bearing carbon.
- 4-bromotoluene from toluene with Br₂ and FeBr₃Draw bromination of toluene at the para position, showing the arenium contributor with the charge on the methyl-bearing carbon.
- Chlorobenzene from benzene with Cl₂ and FeCl₃Draw chlorination of benzene: ring attack on Cl₂, the arenium-ion contributors, and loss of the ring proton to give chlorobenzene.
- Chlorination of chlorobenzene to 1,4-dichlorobenzeneDraw para chlorination of chlorobenzene, including the chloronium contributor that explains why a deactivating halogen still directs ortho/para.
- Benzenesulfonyl chloride from benzene and chlorosulfonic acidDraw formation of the ClSO₂⁺ electrophile from two chlorosulfonic acid molecules and its substitution onto benzene to give benzenesulfonyl chloride.
- Dibromination of biphenyl to 4,4′-dibromobiphenylDraw two para brominations of biphenyl, one on each ring, showing how the second phenyl group stabilizes each arenium ion.
- Acetophenone from benzene and acetic anhydrideDraw AlCl3 activation of acetic anhydride, release of the acetylium ion, its attack by benzene and deprotonation to acetophenone.
- Propanoylation of anisole to 4-methoxypropiophenoneDraw the propanoylium ion from propanoyl chloride and AlCl₃, para attack by anisole with the oxonium contributor, and rearomatization to 4-methoxypropiophenone.
- Friedel–Crafts benzoylation of benzene to benzophenoneDraw formation of the benzoyl acylium ion with AlCl3, its attack by benzene and deprotonation of the arenium ion to benzophenone.
- Friedel–Crafts acetylation of biphenyl to 4-acetylbiphenylDraw the acetylium ion from acetyl chloride and AlCl₃, its attack para to the ring junction of biphenyl and rearomatization to 4-acetylbiphenyl.
- Phenacyl chloride from benzene and chloroacetyl chlorideDraw acylium ion formation from chloroacetyl chloride, attack by benzene and rearomatization to phenacyl chloride, leaving the CH₂–Cl bond intact.
- Acetylation of furan to 2-acetylfuranDraw activation of acetic anhydride by BF3, C2 attack of furan on the acetylium ion, heteroatom stabilisation of the cation and rearomatisation to 2-acetylfuran.
- Intramolecular acylation of 3-phenylpropanoyl chloride to 1-indanoneDraw the acylium ion from 3-phenylpropanoyl chloride, its capture by the ortho ring carbon to close a five-membered ring, and rearomatisation to 1-indanone.
- 2-Methyl-1-phenylpropan-1-one from isobutyryl chlorideDraw the isobutyryl acylium ion from isobutyryl chloride and AlCl3, its attack by benzene and rearomatisation to 2-methyl-1-phenylpropan-1-one, and see why the acyl group does not rearrange.
- Acetylation of m-xylene to 2,4-dimethylacetophenoneDraw the acylium ion from acetyl chloride and AlCl3, its capture by m-xylene at the carbon ortho to one methyl and para to the other, and rearomatisation to 2,4-dimethylacetophenone.
- Acetylation of naphthalene at C2 in nitrobenzeneDraw acetylium ion formation and attack of naphthalene at C2, explaining why the bulky solvated electrophile prefers C2 over the electronically favored C1.
- 2-Benzoylbenzoic acid from benzene and phthalic anhydrideDraw AlCl₃ opening of phthalic anhydride to an acylium ion, attack by benzene and rearomatization to 2-benzoylbenzoic acid.
- Pivaloyl chloride and benzene give tert-butylbenzeneDraw ionisation of pivaloyl chloride by AlCl3, loss of carbon monoxide from the pivaloyl acylium ion to the tert-butyl cation, and its capture by benzene to give tert-butylbenzene.
- Succinoylation of benzene to 4-oxo-4-phenylbutanoic acidDraw AlCl3-promoted ring opening of succinic anhydride to an acylium ion, its attack by benzene and rearomatisation to 4-oxo-4-phenylbutanoic acid.
- Acetylation of thiophene to 2-acetylthiopheneDraw activation of acetic anhydride by SnCl4, C2 attack of thiophene on the acetylium ion, heteroatom stabilisation of the cation and rearomatisation to 2-acetylthiophene.
- Friedel–Crafts acetylation of toluene to 4-methylacetophenoneDraw the acylium ion from acetyl chloride and AlCl3, para attack by toluene and deprotonation to 4-methylacetophenone.
- sec-Butylbenzene from benzene and 1-chlorobutaneDraw AlCl₃ activation of 1-chlorobutane with a 1,2-hydride shift to the sec-butyl cation, ring attack and deprotonation to sec-butylbenzene.
- Isopropylbenzene (cumene) from benzene and 1-chloropropaneDraw AlCl₃ activation of 1-chloropropane with a 1,2-hydride shift to the isopropyl cation, ring attack and deprotonation to give isopropylbenzene (cumene).
- Friedel–Crafts alkylation of benzene to sec-butylbenzeneDraw the AlCl3 activation of 2-chlorobutane, attack of benzene on the 2-butyl cation, and deprotonation of the arenium ion to sec-butylbenzene.
- tert-Pentylbenzene from benzene, 3-methyl-1-butene and HFDraw Markovnikov protonation of 3-methyl-1-butene by HF, the 1,2-hydride shift to the tertiary cation, ring attack and deprotonation to tert-pentylbenzene.
- Isopropylation of anisole with 2-propanol and H2SO4Draw formation of the isopropyl cation from 2-propanol and sulfuric acid, para attack by anisole with oxonium stabilization, and deprotonation to 4-isopropylanisole.
- Friedel–Crafts benzylation of benzene to diphenylmethaneDraw ionisation of benzyl chloride with AlCl3, attack of benzene on the benzyl cation and loss of the ring proton to give diphenylmethane.
- Cyclopentylbenzene from benzene and cyclopentanolDraw protonation of cyclopentanol, loss of water to the cyclopentyl cation, ring attack by benzene and deprotonation to cyclopentylbenzene.
- Ethylbenzene from benzene, ethyl bromide and AlBr3Draw AlBr₃ complexation of ethyl bromide, displacement of AlBr₄⁻ by the benzene ring at the CH₂ carbon, and deprotonation to ethylbenzene.
- 2-Phenylethanol from benzene and ethylene oxide with AlCl3Draw AlCl₃ coordination to ethylene oxide, ring opening by benzene at an epoxide carbon, and rearomatization to 2-phenylethanol.
- tert-Butylbenzene from benzene and isobutylene with H2SO4Draw Markovnikov protonation of isobutylene to the tert-butyl cation, its capture by benzene and loss of the ring proton to tert-butylbenzene.
- tert-Pentylbenzene from benzene and neopentyl chlorideDraw AlCl₃ activation of neopentyl chloride with a 1,2-methyl shift to the tertiary tert-pentyl cation, ring attack and deprotonation to tert-pentylbenzene.
- Friedel–Crafts methylation of toluene to p-xyleneDraw activation of chloromethane by AlCl3, methyl transfer to the para carbon of toluene and deprotonation to p-xylene.
- tert-Butylbenzene from benzene and tert-butanolDraw protonation of tert-butanol, loss of water to the tert-butyl cation, attack by benzene and deprotonation to tert-butylbenzene.
- tert-Butylbenzene from benzene and tert-butyl chlorideDraw AlCl₃ activation of tert-butyl chloride, formation of the tert-butyl cation, ring attack, and deprotonation by AlCl₄⁻ to give tert-butylbenzene.
- Tetralin from 1-chloro-4-phenylbutane by ring closureDraw AlCl₃ activation of 1-chloro-4-phenylbutane, ring closure by the ortho carbon onto the CH₂–Cl carbon and deprotonation to tetralin.
- Cyclohexylation of toluene with cyclohexene and H2SO4Draw protonation of cyclohexene by sulfuric acid, para attack of toluene on the cyclohexyl cation and deprotonation to 1-cyclohexyl-4-methylbenzene.
- Friedel–Crafts isopropylation of toluene to p-cymeneDraw formation of the isopropyl cation, para attack by toluene with the methyl-stabilised arenium ion, and deprotonation to p-cymene.
- Gattermann–Koch formylation of tolueneDraw protonation of CO to the formyl cation with HCl/AlCl3, para attack by toluene and deprotonation to 4-methylbenzaldehyde.
- Gattermann formylation of mesitylene to mesitaldehydeDraw protonation of HCN (from Zn(CN)2 and HCl) by HCl–AlCl3, attack of mesitylene on the HC≡NH⁺ carbon, rearomatisation and aqueous hydrolysis of the aldimine to 2,4,6-trimethylbenzaldehyde.
- Haworth step 1: toluene and succinic anhydrideDraw AlCl3-promoted ring opening of succinic anhydride to a tethered acylium ion, its para attack by toluene and rearomatisation to 4-(4-methylphenyl)-4-oxobutanoic acid, the first Haworth step.
- Houben–Hoesch synthesis of 2′,4′-dihydroxyacetophenoneDraw protonation of acetonitrile to the nitrilium ion, its attack by resorcinol ortho to one OH and para to the other, and hydrolysis of the ketiminium salt to 2′,4′-dihydroxyacetophenone.
- Iodination of anisole with ICl to 4-iodoanisoleDraw para iodination of anisole by iodine monochloride, choosing iodine as the electrophile and chloride as the leaving group.
- Iodobenzene from benzene with I₂ and HNO₃Draw iodination of benzene by the I⁺ electrophile made from I₂ and HNO₃: ring attack, arenium contributors, and deprotonation by water to give iodobenzene.
- Ipso bromodesilylation of 4-(trimethylsilyl)tolueneDraw bromine attack at the silicon-bearing carbon of 4-(trimethylsilyl)toluene, the arenium ion stabilised by the C–Si bond and the para methyl group, and loss of trimethylsilyl bromide to 4-bromotoluene.
- Ipso protodesilylation of trimethylphenylsilane with D₂SO₄Draw ipso deuteration of trimethylphenylsilane at the silicon-bearing carbon, the β-silicon-stabilised arenium ion, and loss of the trimethylsilyl group to deuteriobenzene.
- Mannich reaction of indole to gramineDraw formation of the dimethylmethyleneiminium ion from formaldehyde and dimethylamine in acetic acid, its attack by C3 of indole and rearomatisation to gramine.
- 4-Nitroacetanilide from acetanilideDraw nitronium formation and para nitration of acetanilide, showing why the acetamido group is a moderate ortho/para director.
- 4-Nitroanisole from anisole with HNO₃ and H₂SO₄Draw nitronium formation and para nitration of anisole, noting how the methoxy oxygen stabilizes the arenium ion.
- 3-Nitrobenzoic acid from benzoic acidDraw nitration of benzoic acid at the meta position and explain why the carboxyl group directs meta.
- 1-Bromo-4-nitrobenzene from bromobenzeneDraw para nitration of bromobenzene and explain why a deactivating halogen still directs ortho/para.
- Nitration of fluorobenzene to 1-fluoro-4-nitrobenzeneDraw nitronium ion formation and para nitration of fluorobenzene, showing the fluoronium contributor that makes fluorine an ortho/para director.
- 1,3,5-Trimethyl-2-nitrobenzene from mesityleneDraw nitration of mesitylene and show that every arenium contributor puts the charge on a methyl-bearing carbon.
- 1,3-Dinitrobenzene from nitrobenzeneDraw nitration of nitrobenzene at the meta position and show that its arenium ion never puts positive charge on the nitro-bearing carbon.
- Nitration of pyridine N-oxide to 4-nitropyridine N-oxideDraw nitronium formation, attack of pyridine N-oxide at C4, the contributor in which the N-oxide oxygen donates its lone pair, and rearomatisation to 4-nitropyridine N-oxide.
- Nitration of pyrrole to 2-nitropyrroleDraw C2 attack of pyrrole on acetyl nitrate, nitrogen stabilisation of the cation and deprotonation by acetate to 2-nitropyrrole.
- Nitration of quinoline to 5-nitroquinolineDraw N-protonation of quinoline, nitronium formation, attack of the quinolinium ion at C5 of the benzo ring, rearomatisation and the bicarbonate workup that frees 5-nitroquinoline.
- Nitration of thiophene to 2-nitrothiopheneDraw C2 attack of thiophene on acetyl nitrate, sulfur stabilisation of the cation and deprotonation by acetate to 2-nitrothiophene.
- 2-Nitrotoluene from toluene with HNO₃ and H₂SO₄Draw nitronium formation and nitration of toluene at an ortho position, where the first-formed cation sits on the methyl-bearing carbon.
- 4-Nitrotoluene from toluene with HNO₃ and H₂SO₄Draw nitronium formation and nitration of toluene at the para position, including the contributor with charge on the methyl-bearing carbon.
- 1-Nitro-3-(trifluoromethyl)benzene by nitrationDraw meta nitration of (trifluoromethyl)benzene and explain the purely inductive meta direction of CF₃.
- 2-Hydroxy-1-naphthaldehyde by Reimer–Tiemann formylationDraw α-elimination of chloroform to dichlorocarbene, its capture by the 2-naphthoxide ion at C1, rearomatisation, and base hydrolysis of the dichloromethyl group to 2-hydroxy-1-naphthaldehyde.
- Benzenesulfonic acid from benzene in hot sulfuric acidDraw sulfonation of benzene by SO₃: ring attack, arenium contributors, deprotonation by hydrogen sulfate and protonation of the sulfonate to benzenesulfonic acid.
- Sulfonation of bromobenzene to 4-bromobenzenesulfonic acidDraw SO3 attack para to bromine, the bromonium contributor that explains the ortho/para direction, and deprotonation and protonation to 4-bromobenzenesulfonic acid.
- Naphthalene-1-sulfonic acid by sulfonation at 80 °CDraw SO3 attack at C1 of naphthalene, the arenium contributor that keeps the second ring aromatic, and deprotonation and protonation to naphthalene-1-sulfonic acid, the kinetic product.
- Naphthalene-2-sulfonic acid by sulfonation at 160 °CDraw SO3 attack at C2 of naphthalene, the arenium contributor that moves charge into the second ring, and deprotonation and protonation to naphthalene-2-sulfonic acid, the thermodynamic product.
- Sulfonation of p-xylene to 2,5-dimethylbenzenesulfonic acidDraw SO3 attack on p-xylene next to a methyl group, the arenium contributors, and deprotonation and protonation to 2,5-dimethylbenzenesulfonic acid.
- Transfer of tert-butyl from 4-tert-butyltoluene to benzeneDraw ipso protonation of 4-tert-butyltoluene by HCl–AlCl3, loss of the tert-butyl cation to give toluene, and its capture by benzene to give tert-butylbenzene.
- Vilsmeier–Haack formylation of N,N-dimethylanilineDraw formation of the chloroiminium (Vilsmeier) reagent from DMF and POCl3, its para attack by N,N-dimethylaniline, and the aqueous hydrolysis of the iminium ion to 4-(dimethylamino)benzaldehyde.
- Vilsmeier–Haack formylation of pyrrole to pyrrole-2-carbaldehydeDraw the chloroiminium (Vilsmeier) reagent from DMF and POCl3, its attack by C2 of pyrrole, loss of chloride and the acetate-buffered hydrolysis of the iminium ion to pyrrole-2-carbaldehyde.
Predict the product 10
- Benzenediazonium chloride: choose the coupling partnerPredict which arene couples with a diazonium salt in azo coupling, and where.
- Birch reduction of anisole: which diene formsPredict the regiochemistry of Birch reduction of an arene bearing an electron-donating group.
- Clemmensen reduction of acetophenone: productPredict the product of Clemmensen reduction of an aryl ketone made by Friedel–Crafts acylation.
- Benzene + acetic anhydride, AlCl3: both productsPredict the organic products when an acid anhydride is the acyl source in Friedel–Crafts acylation.
- Benzene + benzoyl chloride, AlCl3: productPredict the ketone formed by Friedel–Crafts acylation with an aroyl chloride.
- Benzene + 1-chloropropane, AlCl3: main productPredict the rearranged product of Friedel–Crafts alkylation with a primary alkyl chloride.
- Benzene + 2-methylpropene in H2SO4: productPredict the product when an alkene and a strong acid supply the carbocation for ring alkylation.
- Benzene + tert-butyl chloride, AlCl3: productPredict the product of Friedel–Crafts alkylation with a tertiary alkyl chloride.
- p-Xylene + hot KMnO4: productPredict the product of exhaustive benzylic oxidation of a dialkylbenzene.
- Ethylbenzene + NBS and light: productPredict the site of radical bromination on an alkylbenzene side chain.
Classify 6
- Three pictures, one intermediateDistinguish resonance arrows from reaction arrows in σ-complex drawings.
- Match diazonium reagents to their productsClassify the common replacement reactions of arenediazonium salts by product.
- Chlorination of benzene: the Cl2/FeCl3 electrophileIdentify the species that delivers chlorine to benzene in Lewis-acid-catalysed chlorination.
- Identify the nitrating electrophileIdentify the species that attacks the ring in a mixed-acid nitration.
- Identify the sulfonating electrophileIdentify the species that attacks the ring in sulfonation with fuming sulfuric acid.
- What addition–elimination SNAr requiresClassify the structural features an aryl halide needs for addition–elimination substitution.
Compare 4
- The base need not be strongExplain deprotonation of an arenium ion by a weak base.
- Benzene vs cyclohexene with Br2Compare how an alkene and benzene react with bromine.
- Styrene + H2, Pd/C at 1 atm: what is reducedCompare the ease of hydrogenating an alkene and an aromatic ring.
- SNAr rates of 1-halo-2,4-dinitrobenzenesRank halide leaving groups by their rate in addition–elimination aromatic substitution.
Calculate 2
- Balance the isolated nitration stagesAccount for charge and atoms in electrophile capture plus water-mediated proton loss.
- Count arenium contributorsCount the resonance contributors of the arenium ion from benzene.
Find the error 4
- A proton is removed from the wrong carbonDiagnose a deprotonation that cannot immediately rearomatize a σ complex.
- Audit nitrogen after ring attackDiagnose a nitrogen-octet error in a nitration mechanism.
- Chlorobenzene as a Friedel–Crafts alkylating agentExplain why aryl halides cannot serve as the electrophile in Friedel–Crafts alkylation.
- Why nitrobenzene resists Friedel–Crafts alkylationExplain why strongly deactivated rings do not undergo Friedel–Crafts reactions.
Interpret the evidence 8
- Read the two-step energy landscapeInterpret a specified EAS energy profile.
- Acylium ion from acetyl chloride and AlCl3Recognise the acylium ion and its resonance forms as the Friedel–Crafts acylation electrophile.
- Benzyne: the nature of its third bondDescribe the orbital make-up of the extra bond in benzyne and relate it to its reactivity.
- Where is the positive charge?Recognise a valid contributor of the arenium ion.
- Intermediates and transition statesRead the energy diagram of a two-step EAS reaction.
- Nitration of benzene-d6: reading kH/kD ≈ 1Use a kinetic isotope effect near 1 to locate the rate-determining step of nitration.
- Sulfonation of benzene-d6: a small isotope effectInterpret a small primary isotope effect in aromatic sulfonation in terms of a reversible first step.
- Which step is rate-determining?Identify the rate-determining step of electrophilic aromatic substitution.
Work backward 1
- Friedel–Crafts acylation — identify the acyl electrophileReconstruct the bond-forming partner from a specified arenium ion.
Plan a synthesis 5
- Removing SO3H from benzenesulfonic acidChoose conditions that reverse aromatic sulfonation.
- Reagents for acylationChoose reagents for Friedel–Crafts acylation of benzene.
- Reagents for brominationChoose reagents for brominating benzene.
- Reagents for nitrationChoose reagents for nitrating benzene.
- Reagents for sulfonationChoose reagents for sulfonating benzene.
Explain why 5
- What the first bond formation changesIdentify the structural origin of lost aromaticity in an arenium ion.
- Propanoyl chloride acylation: why no rearrangementExplain why the acylium ion in Friedel–Crafts acylation does not undergo carbocation rearrangement.
- Why acylation needs a full equivalent of AlCl3Explain why Friedel–Crafts acylation consumes rather than recycles the Lewis acid.
- Why lose H⁺ rather than add Br⁻?Explain why the arenium ion loses a proton instead of adding a nucleophile.
- Toluene to 2-bromotoluene: why sulfonate firstExplain how a removable SO3H group steers substitution to the ortho position.
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