Organic Chemistry 2 · Aromatic systems
Substituent effects and directing: practice problems
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- Draw methoxy donation into the ring
- An amino group stabilizes a σ complex
- Draw how a nitro group drains the ring
- Bromination of 2-aminopyridine at C5
- Acetylation of 2-methylfuran at C5 with BF3
- NBS bromination of 2-methylthiophene at C5
- Bromination of 2-nitrotoluene para to methyl
- Bromination of 3-methylanisole para to methoxy
- NBS bromination of 3-methylthiophene at C2
Draw the mechanism 53
- Draw methoxy donation into the ringShow oxygen lone-pair donation and compensating ring π displacement.
- An amino group stabilizes a σ complexSupply an octet to an ipso carbocation and distinguish donor stabilization from rearomatization.
- Draw how a nitro group drains the ringGenerate the nitro-group and ring contributors of nitrobenzene and use them to explain deactivation and meta direction.
- Bromination of 2-aminopyridine at C5Draw bromination of 2-aminopyridine at C5 and show how the amino group, not the ring nitrogen, sets the site.
- Acetylation of 2-methylfuran at C5 with BF3Draw the BF3-catalysed acetylation of 2-methylfuran at its free α carbon, C5.
- NBS bromination of 2-methylthiophene at C5Draw the NBS bromination of 2-methylthiophene at its free α carbon and show how methyl and sulfur both stabilize the σ complex.
- Bromination of 2-nitrotoluene para to methylDraw the bromination of 2-nitrotoluene para to the methyl group and explain why that carbon beats the other reinforced position.
- Bromination of 3-methylanisole para to methoxyDraw the bromination of 3-methylanisole para to the methoxy group and explain why C4 beats the crowded C2.
- NBS bromination of 3-methylthiophene at C2Draw the NBS bromination of 3-methylthiophene at C2 and explain why C2 beats the other α carbon, C5.
- Bromination of 3-nitrotoluene: the activator decidesDraw bromination of 3-nitrotoluene para to the methyl group and explain why the activating group controls the site.
- Nitration of 4-bromoanisole ortho to methoxyDraw the nitration of 4-bromoanisole in acetic acid and explain why the methoxy group, not bromine, decides where the nitro group goes.
- Nitration of 4-chlorophenol ortho to OHDraw nitration of 4-chlorophenol ortho to the OH group and show why OH, not Cl, directs.
- Bromination of 4-methylacetanilide ortho to NHAcDraw the bromination of 4-methylacetanilide ortho to the acetamido group and explain why the amide beats the methyl group.
- Nitration of 4-methylanisole ortho to methoxyDraw nitration of 4-methylanisole at the carbon ortho to the methoxy group and show why that site wins.
- Donor–acceptor delocalization in 4-nitroanilineDraw the through-conjugation contributor that carries the amino lone pair of 4-nitroaniline onto the para nitro group.
- Chlorination of 4-nitrotoluene ortho to methylDraw the chlorination of 4-nitrotoluene ortho to the methyl group, where the methyl and nitro groups direct to the same carbon.
- Nitration of 4-tert-butyltoluene ortho to methylDraw the nitration of 4-tert-butyltoluene ortho to the methyl group and explain why steric hindrance decides between two alkyl directors.
- Para bromination of acetanilideDraw para bromination of acetanilide, showing nitrogen donation into the σ complex.
- Draw the ring-donation contributors of acetanilidePush the amide nitrogen lone pair into the ring and relay the negative charge to the para carbon.
- Draw how an acetyl group withdraws ring electron densityPull ring π electrons onto the carbonyl oxygen and move the resulting positive charge from an ortho carbon to the para carbon.
- Protonating aniline switches off donationProtonate aniline on nitrogen with sulfuric acid and decide how the anilinium group directs substitution.
- Bromination of 4-methoxybenzaldehyde ortho to OMeDraw bromination of 4-methoxybenzaldehyde ortho to the methoxy group and show the oxonium contributor that makes that site win.
- Ortho bromination of anisole through an oxonium contributorDraw ortho bromination of anisole, including the oxonium contributor of the σ complex.
- Para chlorination of anisole in acetic acidDraw the para chlorination of anisole with Cl2 in acetic acid, including the oxonium contributor of the σ complex.
- Meta bromination of benzaldehyde: σ complex choiceDraw the meta bromination of benzaldehyde and show why its σ complex never puts the positive charge next to the CHO group.
- Bromination of benzanilide: which ring reactsDraw the bromination of benzanilide para to the NH group and explain why the nitrogen-bound ring reacts instead of the benzoyl ring.
- Meta nitration of benzonitrileDraw the meta nitration of benzonitrile and explain how the cyano group decides the site of attack.
- Draw how a nitrile group withdraws ring electron densityPush ring π electrons onto the nitrile nitrogen and move the positive charge from an ortho carbon to the para carbon.
- Para bromination of biphenylDraw para bromination of biphenyl and show how the second ring delocalizes the positive charge of the σ complex.
- Draw the lone-pair donation contributors of chlorobenzenePush a chlorine lone pair into the ring and relay the negative charge to the para carbon.
- Para sulfonation of chlorobenzene with SO3Draw the para sulfonation of chlorobenzene with SO3 in sulfuric acid, including the chloronium contributor and the final protonation of the sulfonate.
- Para nitration of cumene: alkyl size and positionDraw the para nitration of cumene and explain how the isopropyl group directs ortho/para yet favours para.
- Meta nitration of N,N-dimethylaniline in conc. H2SO4Draw the nitration of N,N-dimethylaniline in concentrated sulfuric acid, where the protonated anilinium ion is attacked meta, and the workup that frees the amine.
- Friedel–Crafts acetylation of fluorobenzene at paraDraw the Friedel–Crafts acetylation of fluorobenzene para to fluorine, including the σ-complex contributor in which fluorine shares a lone pair.
- Vilsmeier formylation of furan at C2Draw the Vilsmeier–Haack formylation of furan at C2, from chloroiminium formation through hydrolysis to furan-2-carbaldehyde.
- Acetylation of indole at C3 with Et2AlClDraw the Et2AlCl-promoted acetylation of indole at C3 and explain why C3, not C2, is attacked.
- Nitration of isoquinoline at C5Draw nitration of isoquinoline at C5 through the isoquinolinium ion and explain why the benzenoid ring reacts.
- Nitration of m-xylene at C4Draw nitration of m-xylene at C4 and show that its σ complex is stabilized by both methyl groups.
- Meta nitration of methyl benzoate at 0 °CDraw the meta nitration of methyl benzoate, from nitronium formation to methyl 3-nitrobenzoate.
- Nitration of naphthalene at C1Draw nitration of naphthalene at C1 and the σ-complex contributor that keeps the second ring benzenoid.
- Bromination of p-toluic acid: reinforcing directorsDraw the bromination of p-toluic acid ortho to the methyl group and show how the two directors reinforce each other.
- Friedel–Crafts acetylation of p-xyleneDraw the Friedel–Crafts acetylation of p-xylene and explain why only one ring product can form.
- Draw the oxygen-donation contributors of phenolPush the OH lone pair into the ring and relay the negative charge from an ortho carbon to the para carbon.
- Para bromination of phenyl acetateDraw para bromination of phenyl acetate, showing how the ester oxygen stabilizes the σ complex.
- Nitration of pyridine at C3Draw nitration of pyridine at C3 and show that its σ complex never places the positive charge on nitrogen.
- Trichloroacetylation of pyrrole at C2Draw the uncatalysed trichloroacetylation of pyrrole at C2 and explain why no Lewis acid is needed.
- Para bromination of tert-butylbenzeneDraw the para bromination of tert-butylbenzene and show the σ-complex contributor that the tert-butyl group stabilizes.
- Bromination of thiophene at C2Draw bromination of thiophene at C2, including the sulfonium contributor of the σ complex.
- Chlorination of toluene at the para positionDraw para chlorination of toluene, including the σ-complex contributor that puts the positive charge on the methyl-bearing carbon.
- Para nitration of (trifluoromethoxy)benzeneDraw the para nitration of (trifluoromethoxy)benzene and explain how OCF3 deactivates the ring yet still directs ortho/para.
- Meta bromination of (trifluoromethyl)benzeneDraw the meta bromination of (trifluoromethyl)benzene and explain why a group that withdraws only by induction still directs meta.
- Meta nitration of the trimethylanilinium ionDraw nitration of the trimethylanilinium ion at the meta position and show that its σ complex never puts positive charge next to N+.
- Friedel–Crafts acetylation of 1,2-dimethoxybenzeneDraw the Friedel–Crafts acetylation of 1,2-dimethoxybenzene at C4 and explain why the acyl group goes para to one methoxy group.
Predict the product 13
- A director changes after protonationPredict directing behavior from the actual protonation state.
- Nitration product of 1,3-dichlorobenzenePredict the mononitration product of 1,3-dichlorobenzene from two reinforcing halogen directors.
- Bromination site in 3-nitrotoluenePredict where bromination occurs on 3-nitrotoluene when an activator and a deactivator disagree.
- Predict the nitration product of 4-methylanisolePredict the major mononitration product of 4-methylanisole when a methoxy and a methyl group compete.
- Nitration product of 4-chlorophenolPredict the mononitration product of 4-chlorophenol by deciding which ortho/para director is stronger.
- Friedel–Crafts acylation product of bromobenzenePredict the major product of Friedel–Crafts acetylation of bromobenzene.
- Major product of tert-butylbenzene brominationPredict the major product of brominating tert-butylbenzene with Br2 and FeBr3 and explain why almost no ortho product forms.
- Major product of toluene bromination with Br2/FeBr3Predict the major product of brominating toluene with Br2 and FeBr3.
- Major product of acetanilide chlorination with Cl2/FeCl3Predict the major product of chlorinating acetanilide with Cl2 and FeCl3.
- Major product of anisole nitration with HNO3/H2SO4Predict the major product of nitrating anisole with nitric and sulfuric acids.
- Major product of benzoic acid nitrationPredict the major product of nitrating benzoic acid with nitric and sulfuric acids.
- Major product of benzonitrile nitrationPredict the major product of nitrating benzonitrile with nitric and sulfuric acids.
- Major product of nitrobenzene sulfonation with SO3Predict the product of sulfonating nitrobenzene with SO3 in sulfuric acid.
Classify 12
- Direction is not activationClassify the rate and positional effects of chlorine separately.
- Classify NHCOCH3Classify the acetamido (–NHCOCH3) substituent by its effect on EAS rate and orientation.
- Classify an acetyl groupClassify the acetyl (–COCH3) substituent by its effect on EAS rate and orientation.
- Classify a methoxy groupClassify the methoxy (–OCH3) substituent by its effect on EAS rate and orientation.
- Classify a nitro groupClassify the nitro (–NO2) substituent by its effect on EAS rate and orientation.
- Classify tert-butylClassify the tert-butyl substituent and explain its strong para preference.
- Classify CF3Classify the trifluoromethyl (–CF3) substituent by its effect on EAS rate and orientation.
- Classify –N(CH3)3⁺Classify the trimethylammonio (–N(CH3)3⁺) substituent by its effect on EAS rate and orientation.
- IUPAC name of meta bromonitrobenzeneName a meta-disubstituted benzene with two prefix-only substituents using alphabetical numbering.
- Match anisole and cumene to their structuresRecall the structures behind the common names anisole and cumene.
- Name the 1,3 relationship in 3-chlorotolueneIdentify the ortho/meta/para prefix for two substituents in a 1,3 relationship on benzene.
- Name the tribromo product of phenolName a trisubstituted phenol by numbering from the carbon of the parent OH group.
Compare 6
- Which end of the group meets the ring?Compare directing behavior of carbonyl-carbon versus oxygen attachment.
- Rank four activatorsRank NH2, OH, OCH3 and CH3 by how strongly they activate benzene toward EAS.
- Rank four deactivatorsRank NO2, CF3, COCH3 and Cl by how strongly they deactivate benzene toward EAS.
- Anisole versus phenyl acetate in EASCompare anisole and phenyl acetate as EAS substrates by asking how available the oxygen lone pair is.
- Rank phenol, anisole, acetophenone and nitrobenzeneRank phenol, anisole, acetophenone and nitrobenzene by their rate of electrophilic aromatic substitution.
- Rank toluene, benzene and chlorobenzene for nitrationRank toluene, benzene and chlorobenzene by their rate of electrophilic nitration.
Calculate 7
- Equivalent positions are not extra productsUse ring symmetry to count positional isomers.
- Count arenium contributorsCount the resonance contributors of the σ-complex formed by para attack on anisole.
- Count the mononitration products of p-xyleneCount the constitutional isomers formed by mononitration of p-xylene using ring symmetry.
- Count the ring monobromides of m-xyleneCount the constitutional isomers possible for ring monobromination of m-xylene using symmetry.
- Count the ring monobromides of o-xyleneCount the constitutional isomers formed by ring monobromination of o-xylene using symmetry.
- Count the possible mononitrotoluenesCount the constitutional isomers possible for mononitration of toluene using ring symmetry.
- Orders of magnitude between toluene and nitrobenzeneCalculate how many orders of magnitude separate the nitration rates of toluene and nitrobenzene.
Find the error 2
- Assess regioselectivity evidenceDiagnose unsupported precision in regioselectivity predictions.
- Spot the false oxygen-donation contributor for meta attackDiagnose which drawing does not belong among the σ-complex contributors from meta bromination of phenol.
Interpret the evidence 4
- Two substituents agreeIdentify shared directing positions before judging steric effects.
- Per-site reactivity in the nitration of tolueneUse the ortho:meta:para ratio of toluene nitration to compare the reactivity of a single ortho and a single para position.
- Why tert-butylbenzene nitrates mostly paraInterpret why tert-butylbenzene gives far more para product on nitration than toluene does.
- Pick the oxonium contributor of the anisole σ complexIdentify the σ-complex contributor of anisole bromination in which the methoxy oxygen donates its lone pair.
Work backward 1
- Infer activation from supplied ratesSeparate observed activation from directing assumptions.
Explain why 4
- Why meta avoids the worst contributorExplain nitro-group meta direction using σ-complex destabilization.
- Why a methyl group directs ortho/para and activatesExplain why a methyl group makes toluene an ortho/para-directing, activated ring using its σ-complex contributors.
- Why m-xylene avoids the carbon between its methylsExplain why nitration of m-xylene gives 4-nitro-m-xylene rather than 2-nitro-m-xylene.
- Why phenol in NaOH brominates three timesExplain why bromination of phenol in aqueous NaOH gives 2,4,6-tribromophenol.
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