Organic Chemistry 2 · Aromatic systems
Aromatic substitution exam review: practice problems
79 problems, each with its worked solution. Open one to read every step, or filter by tag.
Start drawing: Aromatic substitution exam review
Tap one to draw it yourself with every arrow checked, or watch the steps. No sign-up.
- Bromination of benzene with Br₂ and FeBr₃
- Azo coupling of benzenediazonium with phenoxide
- Bromination of phenol without a Lewis acid
- Chlorination of nitrobenzene
- Removing a sulfonic acid blocking group: 2-bromotoluene
- Friedel–Crafts acylation of benzene with propanoyl chloride
- Intramolecular Friedel–Crafts acylation: 1-tetralone
- Alkylation of benzene with cyclohexene and sulfuric acid
- Friedel–Crafts alkylation with 1-chloro-2-methylpropane: a hydride shift
Draw the mechanism 39
- Azo coupling of benzenediazonium with phenoxideDraw the attack of phenoxide's para carbon on the terminal nitrogen of benzenediazonium, the deprotonation that restores the ring, and the acid workup that gives 4-(phenyldiazenyl)phenol.
- Bromination of benzene with Br₂ and FeBr₃Draw how FeBr₃ activates Br₂, how benzene attacks the activated bromine to give an arenium ion, and how FeBr₄⁻ removes the ring proton to give bromobenzene and regenerate the catalyst.
- Bromination of phenol without a Lewis acidDraw the attack of phenol's para carbon on Br₂, pushed by the hydroxyl lone pair, and the deprotonation by bromide that gives 4-bromophenol and HBr.
- Chlorination of nitrobenzeneDraw the activation of Cl₂ by FeCl₃, attack by the carbon meta to the nitro group, and deprotonation by FeCl₄⁻ to give 1-chloro-3-nitrobenzene.
- Removing a sulfonic acid blocking group: 2-bromotolueneDraw the ipso protonation of 3-bromo-4-methylbenzenesulfonate by hydronium and the loss of SO₃ that removes the blocking group and gives 2-bromotoluene.
- Friedel–Crafts acylation of benzene with propanoyl chlorideDraw the formation of the propanoyl acylium ion from propanoyl chloride and AlCl₃, its capture by benzene, and the deprotonation that gives 1-phenylpropan-1-one.
- Intramolecular Friedel–Crafts acylation: 1-tetraloneDraw acylium-ion formation from 4-phenylbutanoyl chloride, ring closure onto the ortho carbon of the same benzene ring to form a six-membered ring, and deprotonation to give 1-tetralone.
- Alkylation of benzene with cyclohexene and sulfuric acidDraw the protonation of cyclohexene by sulfuric acid, the attack of benzene on the cyclohexyl cation, and the deprotonation by hydrogen sulfate that gives cyclohexylbenzene.
- Friedel–Crafts alkylation with 1-chloro-2-methylpropane: a hydride shiftDraw how the 1-chloro-2-methylpropane–AlCl₃ complex ionises with a hydride shift to the tert-butyl cation, how benzene captures that cation, and how AlCl₄⁻ restores the ring to give tert-butylbenzene.
- Friedel–Crafts tert-butylation of tolueneDraw the formation of the tert-butyl cation, attack by the carbon para to the methyl group of toluene, the arenium contributor that puts the positive charge on the carbon bearing CH₃, and deprotonation to 1-tert-butyl-4-methylbenzene.
- Meta nitration of benzaldehydeDraw the attack of the ring carbon meta to the formyl group on nitronium, a resonance contributor of the arenium ion showing that the charge never reaches the carbon bearing CHO, and the deprotonation that gives 3-nitrobenzaldehyde.
- Nitration of chlorobenzeneDraw nitronium formation in mixed acid, para attack by chlorobenzene with the chlorine lone pair stabilising the arenium ion, and deprotonation by hydrogen sulfate to give 1-chloro-4-nitrobenzene.
- SNAr: methoxide displaces chloride from 1-chloro-2-nitrobenzeneDraw the addition of methoxide to 1-chloro-2-nitrobenzene with the ortho nitro group holding the negative charge of the Meisenheimer complex, then the loss of chloride that gives 2-nitroanisole.
- Regioselective SNAr of 1,2-difluoro-4-nitrobenzene with morpholineDraw the addition of morpholine to the ring carbon para to the nitro group, the proton transfer to a second morpholine, and the loss of fluoride that gives 4-(2-fluoro-4-nitrophenyl)morpholine.
- Sulfonation of toluene with fuming sulfuric acidDraw the attack of the carbon para to the methyl group of toluene on SO₃, the deprotonation that restores the ring, and the proton transfer that gives 4-methylbenzenesulfonic acid.
- Azo coupling of benzenediazonium with 2-naphthol to Sudan IDraw deprotonation of 2-naphthol, C1 attack of the naphthoxide on benzenediazonium, rearomatisation and protonation to give 1-phenylazo-2-naphthol.
- Azo coupling of benzenediazonium with N,N-dimethylaniline: methyl yellowDraw para attack of N,N-dimethylaniline on the benzenediazonium ion, the iminium-stabilised arenium ion and deprotonation by acetate to methyl yellow.
- Benzyne amination of 3-bromobenzotrifluorideDraw deprotonation of 3-bromobenzotrifluoride by amide, loss of bromide to the aryne, regioselective amide addition and protonation to give 3-(trifluoromethyl)aniline.
- Triptycene from benzyne and anthraceneDraw benzyne formation from bromobenzene and sodium amide, then its Diels–Alder addition across C9 and C10 of anthracene to give triptycene.
- Benzyne from a silylaryl triflate trapped by furanDraw fluoride attack at silicon, loss of triflate to give benzyne and its Diels–Alder reaction with furan to 1,4-dihydro-1,4-epoxynaphthalene.
- Bromination of 2-methoxynaphthalene at C1Draw C1 attack of 2-methoxynaphthalene on bromine, the methoxy-stabilised arenium ion and loss of the C1 proton to give 1-bromo-2-methoxynaphthalene.
- Bromination of 4-methylanisole to 2-bromo-4-methylanisoleDraw attack of 4-methylanisole on bromine ortho to methoxy, the oxocarbenium arenium ion and loss of the ring proton to give 2-bromo-4-methylanisole.
- Bromination of 4-nitroacetanilide at C2Draw attack of 4-nitroacetanilide on bromine ortho to the acetamido group, the C=N⁺ arenium ion and loss of the ring proton to give 2-bromo-4-nitroacetanilide.
- Bromination of acetanilide to 4-bromoacetanilideDraw para attack of acetanilide on bromine, the nitrogen-stabilised arenium ion and loss of the ring proton to give 4-bromoacetanilide.
- Anisole and glutaric anhydride: a Friedel–Crafts keto acidDraw ring opening of glutaric anhydride by AlCl3 to an acylium ion, para attack by anisole, rearomatisation and the acid workup that frees 5-(4-methoxyphenyl)-5-oxopentanoic acid.
- Friedel–Crafts acetylation of chlorobenzene to 4-chloroacetophenoneDraw acylium ion formation from acetyl chloride and AlCl3, para attack by chlorobenzene and deprotonation to 4-chloroacetophenone.
- Friedel–Crafts propanoylation of mesityleneDraw acylium ion formation from propanoyl chloride and AlCl3, attack by mesitylene and loss of the ring proton to give 1-(2,4,6-trimethylphenyl)propan-1-one.
- tert-Butylation of anisole to 4-tert-butylanisoleDraw the tert-butyl cation forming from tert-butanol in sulfuric acid, para attack by anisole and deprotonation to 4-tert-butylanisole.
- Benzene alkylation by 2-chloro-3-methylbutane: hydride shiftDraw ionisation of 2-chloro-3-methylbutane by AlCl3, the 1,2-hydride shift to the tertiary cation and its attack by benzene to give (2-methylbutan-2-yl)benzene.
- Friedel–Crafts isopropylation of p-xyleneDraw ionisation of 2-chloropropane by AlCl3, attack of p-xylene on the isopropyl cation and loss of the ring proton to give 2-isopropyl-1,4-dimethylbenzene.
- Nitration of 4-fluoroanisole: methoxy outdirects fluorineDraw nitronium ion formation from nitric acid, attack of 4-fluoroanisole ortho to methoxy and rearomatisation to 4-fluoro-2-nitroanisole.
- Nitration of anisole to 2-nitroanisoleDraw nitronium formation, ortho attack by anisole with the methoxy oxygen stabilising the arenium ion, and deprotonation to 2-nitroanisole.
- Nitration of 1,3-dimethoxybenzene to 2,4-dimethoxy-1-nitrobenzeneDraw nitronium formation from nitric acid, attack at C4 of 1,3-dimethoxybenzene with methoxy stabilisation, and loss of the ring proton.
- Nitration of methyl 4-methylbenzoate to the 3-nitro esterDraw nitronium ion formation, attack of methyl 4-methylbenzoate at the carbon ortho to methyl and meta to the ester, and rearomatisation to methyl 4-methyl-3-nitrobenzoate.
- Nitration of naphthalene to 1-nitronaphthaleneDraw nitronium formation, attack at C1 of naphthalene with a benzenoid-preserving arenium ion, and deprotonation to 1-nitronaphthalene.
- SNAr of 1-chloro-2,4-dinitrobenzene with anilineDraw addition of aniline to 1-chloro-2,4-dinitrobenzene to form the Meisenheimer complex, loss of chloride and deprotonation to give 2,4-dinitrodiphenylamine.
- SNAr of 4-fluorobenzonitrile with phenoxideDraw deprotonation of phenol by carbonate, addition of phenoxide to 4-fluorobenzonitrile and loss of fluoride to give 4-phenoxybenzonitrile.
- SNAr of 1-fluoro-4-nitrobenzene with piperidineDraw piperidine adding to 1-fluoro-4-nitrobenzene to give the Meisenheimer complex, loss of fluoride, and deprotonation to 1-(4-nitrophenyl)piperidine.
- Sulfonation of nitrobenzene to 3-nitrobenzenesulfonic acidDraw meta attack of nitrobenzene on sulfur trioxide, deprotonation by hydrogen sulfate and protonation of the sulfonate.
Predict the product 7
- Amination of 2-bromoanisole with NaNH₂Predict the regiochemistry of nucleophilic addition to an unsymmetrical benzyne bearing an inductively withdrawing group.
- Amination of 4-chlorotoluene with NaNH₂Predict the cine-substitution products of an unactivated aryl halide reacting through benzyne.
- Brominate 4-nitrotoluenePredict the position of substitution when two ring substituents reinforce each other's directing effects.
- Trapping benzyne with furanPredict the Diels–Alder adduct when benzyne is generated in the presence of furan.
- Friedel–Crafts with 2-chlorobutanePredict the alkylbenzene from Friedel–Crafts alkylation of benzene with 2-chlorobutane.
- Nitrating 4-chloroanisolePredict nitration regiochemistry when two ortho/para directors compete on 4-chloroanisole.
- Sanger's reagent with an aminePredict the SNAr product of 1-fluoro-2,4-dinitrobenzene with a primary amine.
Classify 6
- Which arene will not undergo Friedel–Crafts acylation?Identify a ring too deactivated for Friedel–Crafts acylation.
- Which species is aromatic?Apply Hückel's 4n + 2 rule to cyclic ions and neutral polyenes, including the effect of charge on the π count.
- Which nitrogen lone pair is in the aromatic sextet?Decide whether a heteroatom lone pair belongs to the aromatic π system in pyrrole and pyridine and connect it to basicity.
- Which aryl chloride undergoes SNAr?Recognise the substrate requirement for nucleophilic aromatic substitution by addition–elimination.
- Is azulene aromatic?Apply Hückel criteria to the fused 5–7 bicyclic hydrocarbon azulene.
- Find the meta directorIdentify the meta-directing group among common benzene substituents.
Compare 4
- Rank three ring hydrocarbons by acidityRank hydrocarbon acidity from the delocalisation and aromaticity of the conjugate-base anions.
- Rank five arenes by rate of nitrationOrder monosubstituted benzenes by EAS rate from the activating or deactivating character of the substituent.
- Rank aryl chlorides for SNArRank aryl chlorides in SNAr reactivity by counting ortho/para nitro groups.
- Rank arenes for brominationRank five arenes by rate of electrophilic bromination from substituent donor strength.
Calculate 3
- π electrons in the cyclooctatetraene dianionCount the π electrons of a reduced annulene and use the count to explain a change in shape.
- Partial rate factor for para nitration of tolueneCalculate a partial rate factor from a relative rate and an isomer distribution.
- Count π electrons in the tropylium ionCount the π electrons of a cyclic carbocation to decide whether it is aromatic.
Find the error 1
- A Friedel–Crafts plan for an aminoketoneFind the flaw in a Friedel–Crafts acylation planned on a free arylamine.
Interpret the evidence 4
- Where did the ¹⁴C label go?Interpret an isotope-labelling result as evidence for a benzyne intermediate.
- What a missing isotope effect meansInterpret the absence of a kinetic isotope effect in EAS nitration as evidence that attack, not deprotonation, is rate-determining.
- A 5H multiplet at 7.2 ppm: identify the C9H12 areneUse a five-proton aromatic multiplet to identify a monosubstituted benzene and assign its side chain.
- Two 2H aromatic doublets: which substitution pattern?Recognise the two-doublet aromatic ¹H NMR pattern of a para-disubstituted benzene.
Work backward 1
- Which intermediate leads to 3-nitrobenzoic acid?Work backwards from a meta-disubstituted target to the intermediate that sets up the correct directing effect.
Plan a synthesis 9
- Turn a meta director into an ortho/para directorChoose a reagent that converts an aromatic nitro group into an amino group.
- Make 1-chloro-3-propylbenzene from benzenePlan a three-step arene synthesis that uses an acyl group as a temporary meta director and avoids carbocation rearrangement.
- Make 2-bromotoluene free of the para isomerUse a reversible sulfonic acid blocking group to direct a substitution ortho to an alkyl group.
- Make 1-bromo-3-nitrobenzene from benzeneChoose the order of two electrophilic substitutions from the relationship of the substituents in the target.
- Make 4-bromobenzoic acid from tolueneOrder a ring substitution and a side-chain oxidation so that the directing effect of the side chain is used before it changes.
- Which sequence gives butylbenzene?Plan a route to butylbenzene that avoids carbocation rearrangement.
- 3-Aminobenzoic acid from tolueneOrder side-chain oxidation, nitration and nitro reduction to make 3-aminobenzoic acid from toluene.
- 4-Chlorobenzenesulfonic acid from benzene in two stepsChoose the order of chlorination and sulfonation that puts the two groups para on benzene.
- Order the route from toluene to 4-nitrobenzoic acidOrder nitration, isomer separation and side-chain oxidation to make 4-nitrobenzoic acid from toluene.
Explain why 5
- Why does aniline give meta product in mixed acid?Explain how protonation of an amino group in strong acid converts an ortho/para director into a meta director.
- Why alkylation over-reacts and acylation does notExplain the difference in over-reaction between Friedel–Crafts alkylation and acylation from the effect of the group introduced.
- One bromide is a salt, the other is notExplain a difference in ionisation between two cyclic allylic bromides from the aromaticity of the cations they would form.
- Why acylation stops after oneExplain why Friedel–Crafts acylation gives monosubstitution while alkylation over-reacts.
- Why cyclopropenone is so polarExplain the large dipole of cyclopropenone with an aromatic charge-separated contributor.
Stuck on your own homework?
Snap it — first scan free, no sign-up
Scanning every week? Scan Standard: for about problems