Organic Chemistry 1 · Exam review
Acids, bases and resonance: exam review: practice problems
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- Sulfuric acid protonates acetic acid
- LDA deprotonates acetonitrile
- Hydroxide frees aniline from anilinium
- Acetic acid protonates benzamidine
- Protonating cyclohex-2-en-1-one
- Bicarbonate deprotonates dimedone
- Acetic acid protonates 4-(dimethylamino)pyridine
- n-Butyllithium deprotonates fluorene
- Acetic acid protonates imidazole
Draw the mechanism 60
- Sulfuric acid protonates acetic acidDraw sulfuric acid protonating the carbonyl oxygen of acetic acid, then the equivalent contributor that puts the positive charge on the other oxygen.
- LDA deprotonates acetonitrileDraw LDA removing a hydrogen from the methyl group of acetonitrile, then the contributor that places the negative charge on nitrogen.
- Hydroxide frees aniline from aniliniumDraw hydroxide removing a proton from the anilinium ion, then the charge-separated contributor that shows the aniline nitrogen lone pair delocalized into the ring, and return to the neutral major contributor.
- Acetic acid protonates benzamidineDraw acetic acid protonating the C=NH nitrogen of benzamidine, then the equivalent contributor that puts the positive charge on the other nitrogen.
- Protonating cyclohex-2-en-1-oneDraw hydronium protonating the carbonyl oxygen of cyclohex-2-en-1-one, then the two minor contributors that place the positive charge on the carbonyl carbon and on the β-carbon, and return to the major oxonium contributor.
- Bicarbonate deprotonates dimedoneDraw bicarbonate removing the hydrogen between the two carbonyl groups of dimedone, then the contributor that moves the charge to the other carbonyl oxygen.
- Acetic acid protonates 4-(dimethylamino)pyridineDraw acetic acid protonating the ring nitrogen of DMAP, then the contributor in which the dimethylamino group carries the positive charge, and return to the aromatic pyridinium contributor.
- n-Butyllithium deprotonates fluoreneDraw the butyl carbanion removing a hydrogen from the CH₂ carbon of fluorene, then a minor contributor that moves the negative charge into a benzene ring, and return to the major contributor with the charge on the central carbon.
- Acetic acid protonates imidazoleDraw acetic acid protonating the basic nitrogen of imidazole, then the equivalent contributor of the imidazolium ion.
- Carbonate deprotonates 4-nitrophenolDraw carbonate removing the O–H proton of 4-nitrophenol, move the phenoxide charge through the ring onto an oxygen of the para nitro group, and return to the aromatic phenoxide contributor.
- tert-Butoxide deprotonates 4-nitrotolueneDraw tert-butoxide removing a methyl hydrogen of 4-nitrotoluene, then move the charge through the ring onto an oxygen of the nitro group.
- Hydroxide deprotonates phthalimideDraw hydroxide removing the N–H proton of phthalimide, then the contributor that moves the nitrogen's negative charge onto a carbonyl oxygen.
- LDA deprotonates the methyl group of 4-methylpyridineDraw LDA removing a methyl hydrogen of 4-methylpyridine, then the contributor that places the negative charge on the ring nitrogen.
- Strong acid protonates pyrrole on carbonDraw HCl protonating C2 of pyrrole, then the contributor in which the nitrogen lone pair stabilizes the cation as an iminium ion.
- Triphenylmethanol forms the trityl cation in sulfuric acidDraw sulfuric acid protonating the OH of triphenylmethanol, loss of water to give the triphenylmethyl cation, one minor contributor that places the positive charge in a ring, and the return to the major contributor.
- Hydroxide deprotonates cyclohexane-1,3-dioneDraw hydroxide removing a hydrogen from the CH2 between the carbonyls of cyclohexane-1,3-dione, then the contributor that moves the charge to the second oxygen.
- HCl protonates 1-methylimidazole at N3Draw N3 of 1-methylimidazole taking the proton from HCl, then the resonance arrows that move the positive charge onto the methylated nitrogen.
- Bicarbonate deprotonates 2,4-dinitrophenolDraw bicarbonate removing the O–H proton of 2,4-dinitrophenol, the resonance form with the charge on an ortho nitro oxygen, and carbonic acid losing carbon dioxide.
- HCl protonates 2-aminopyridine on the ring nitrogenDraw the ring nitrogen of 2-aminopyridine taking the proton from HCl, then the resonance arrows that put the positive charge on the amino nitrogen.
- Hydroxide deprotonates 2-nitropropaneDraw hydroxide removing the C2 hydrogen of 2-nitropropane, then the resonance that moves the charge onto oxygen in the nitronate ion.
- LDA forms the kinetic enolate of 2-pentanoneDraw LDA removing a methyl hydrogen of 2-pentanone, then the resonance that gives the less substituted (kinetic) enolate.
- HCl protonates 2-pyridone on oxygenDraw the carbonyl oxygen of 2-pyridone taking the proton from HCl, then the nitrogen lone pair forming the aromatic 2-hydroxypyridinium ion.
- HCl protonates 4-aminopyridine on the ring nitrogenDraw the ring nitrogen of 4-aminopyridine taking a proton from HCl, then the resonance arrows that move the positive charge onto the amino nitrogen.
- Hydroxide deprotonates 4-chlorophenolDraw hydroxide removing the O–H proton of 4-chlorophenol, then the resonance arrows that carry the negative charge to the para carbon bearing chlorine.
- HCl protonates acetamide on oxygenDraw the carbonyl oxygen of acetamide taking the proton from HCl, then the contributor in which the nitrogen lone pair shares the positive charge.
- Methylamine deprotonates acetic acidDraw the methylamine lone pair taking the O–H proton of acetic acid to give methylammonium acetate.
- Acetic acid protonates sodium phenoxideDraw phenoxide removing the O–H proton of acetic acid to give phenol and acetate, then the resonance arrows that share the acetate charge between both oxygens.
- Ethoxide deprotonates 2,4-pentanedioneDraw ethoxide removing a hydrogen from the CH2 between the two carbonyls of 2,4-pentanedione, then the contributor that moves the charge to the other oxygen.
- HCl protonates anilineDraw the nitrogen lone pair of aniline taking the proton from HCl to give the anilinium ion.
- HCl protonates 1H-benzimidazole at N3Draw N3 of 1H-benzimidazole taking the proton from HCl, then the resonance arrows that share the positive charge with N1.
- Bicarbonate deprotonates benzoic acidDraw bicarbonate removing the carboxylic acid proton of benzoic acid, then carbonic acid breaking down to CO2 and water.
- tert-Butoxide deprotonates cyclopentadieneDraw tert-butoxide removing a CH2 hydrogen of cyclopentadiene, then a resonance arrow pair that moves the charge around the ring.
- LDA forms the enolate of cyclopentanoneDraw LDA removing an α-hydrogen of cyclopentanone, then the resonance that moves the charge onto the carbonyl oxygen of the enolate.
- Sodium hydride deprotonates diethyl malonateDraw hydride removing a central CH2 hydrogen of diethyl malonate, then the resonance that places the charge on a carbonyl oxygen.
- n-Butyllithium makes lithium diethylamideDraw the C–Li bond of n-butyllithium removing the N–H proton of diethylamine to give lithium diethylamide and butane.
- Sodium hydride deprotonates dimethyl sulfoneDraw hydride removing a methyl hydrogen of dimethyl sulfone to give the sulfonyl-stabilized carbanion and hydrogen gas.
- Hydroxide deprotonates ethanethiolDraw hydroxide removing the S–H proton of ethanethiol to give the ethanethiolate ion.
- LDA forms the enolate of ethyl acetateDraw LDA removing an α-hydrogen of ethyl acetate and the electron flow that gives the ester enolate.
- Ethoxide forms the ethyl acetoacetate enolateDraw ethoxide removing a hydrogen from the CH2 between the two carbonyls of ethyl acetoacetate, then the resonance that puts the charge on the ketone oxygen.
- HCl protonates guanidineDraw the imine nitrogen of guanidine taking the proton from HCl, then a contributor that moves the positive charge onto another nitrogen.
- Sodium hydride deprotonates hexafluoroisopropanolDraw hydride removing the O–H proton of hexafluoroisopropanol to give the fluorinated alkoxide and hydrogen gas.
- Triethylamine deprotonates hexafluoro-2-propanolDraw triethylamine removing the O–H proton of hexafluoro-2-propanol to give the alkoxide and triethylammonium.
- Concentrated HCl protonates indole at C3Draw the C2=C3 π bond of indole taking a proton from HCl at C3, then the nitrogen lone pair forming the C=N+ bond of the 3H-indolium ion.
- n-Butyllithium converts 2-propanol to lithium 2-propoxideDraw the C–Li bond of n-butyllithium removing the O–H proton of 2-propanol to give lithium 2-propoxide and butane.
- Triethylamine deprotonates malononitrileDraw triethylamine removing a CH2 hydrogen of malononitrile, then the contributor that places the negative charge on a nitrile nitrogen.
- Bicarbonate deprotonates Meldrum's acidDraw bicarbonate removing a CH2 hydrogen of Meldrum's acid, the resonance that gives the enolate, and the loss of CO2 from carbonic acid.
- Sodium hydride deprotonates methanolDraw the hydride ion taking the O–H proton of methanol to give methoxide and hydrogen gas.
- Hydroxide deprotonates nitromethaneDraw hydroxide removing a C–H hydrogen of nitromethane and the electron flow that gives the nitronate ion with C=N.
- Hydroxide deprotonates phenolDraw hydroxide removing the O–H proton of phenol, then the resonance arrows that move the negative charge onto an ortho ring carbon.
- Sodium amide deprotonates phenylacetonitrileDraw the amide ion removing a CH2 hydrogen of phenylacetonitrile to give the α-cyanobenzyl carbanion and ammonia.
- Ethylmagnesium bromide deprotonates phenylacetyleneDraw the C–Mg bond of ethylmagnesium bromide removing the terminal alkyne hydrogen of phenylacetylene, with magnesium moving to the alkyne carbon to give phenylethynylmagnesium bromide and ethane.
- Sodium amide deprotonates propyneDraw the amide ion removing the terminal alkyne hydrogen of propyne to give the propynide ion.
- HCl protonates 1H-pyrazole at N2Draw N2 of 1H-pyrazole taking the proton from HCl, then the resonance arrows that move the positive charge onto N1 through the ring.
- HCl protonates pyridineDraw the pyridine nitrogen lone pair taking the proton from HCl to give pyridinium chloride.
- HCl protonates pyridine N-oxide on oxygenDraw the N-oxide oxygen of pyridine N-oxide taking the proton from HCl to give 1-hydroxypyridinium chloride.
- HCl protonates quinolineDraw the quinoline nitrogen lone pair taking the proton from HCl to give quinolinium chloride.
- Potassium hydroxide deprotonates succinimideDraw hydroxide removing the N–H proton of succinimide, then the resonance arrows that move the charge from nitrogen onto a carbonyl oxygen.
- HCl protonates thiazole on nitrogenDraw the thiazole ring nitrogen taking the proton from HCl to give thiazolium chloride.
- Triethylamine deprotonates thiophenolDraw triethylamine removing the S–H proton of thiophenol to give benzenethiolate and triethylammonium.
- n-Butyllithium deprotonates triphenylmethaneDraw the C–Li bond of n-butyllithium removing the central hydrogen of triphenylmethane to give the trityl anion and butane.
Predict the product 6
- Which hydrogen does ethoxide remove?Predict which carbon acid site of a β-keto ester is deprotonated by an alkoxide.
- An acetylide in an alcohol solventPredict whether a strong carbon base survives in a protic solvent by comparing pKa values.
- One base, two acidsPredict which conjugate base accumulates when one equivalent of a strong base meets two acids of different strength.
- Push an enamine lone pairPredict the contributor produced by a lone-pair-to-bond arrow paired with a π-to-atom arrow.
- Bicarbonate and 4-hydroxybenzoic acid: which proton goes?Predict which acidic proton of 4-hydroxybenzoic acid bicarbonate removes by comparing each pKa with that of carbonic acid.
- Where does an amide take a proton?Predict the protonation site of an amide by comparing the resonance stabilization of each conjugate acid.
Classify 4
- The other contributor of an allylic cationIdentify a valid resonance contributor of an allylic cation by checking that only electrons move.
- Which ion has equivalent contributors?Recognize a species whose two major contributors are equivalent, so its charge is shared equally by two atoms.
- Which base fully deprotonates diethyl malonate?Choose a base that converts diethyl malonate fully into its enolate by comparing the pKa of each base’s conjugate acid with 13.
- Valid resonance contributor of the acetone enolateRecognize a valid resonance contributor: electrons move, atoms and σ bonds stay put.
Compare 11
- From hydrocarbon to carboxylic acidRank five common acid types by reasoning about the stability of each conjugate base.
- Adding chlorines one at a timeRank carboxylic acids by the cumulative inductive effect of α-chlorine substituents.
- Which group activates a CH₃ most?Compare carbon acids by the ability of the attached electron-withdrawing group to stabilize the carbanion.
- Rank four nitrogen compounds as basesRank nitrogen bases by lone-pair delocalization in the base and charge delocalization in the conjugate acid.
- Where the nitro group sits mattersRank substituted phenols by combining the position-dependent resonance effect with the inductive effect of nitro groups.
- Octets versus electronegativityChoose the major contributor of a protonated carbonyl by ranking octet completeness above charge placement.
- Pick the strongest carboxylic acidCompare carboxylic acids by the number of electronegative substituents near the carboxyl group.
- Which aniline holds its lone pair tightest?Compare substituted anilines as bases using position-dependent resonance withdrawal.
- Rank five carbon acids by C–H acidityOrder carbon acids by how well their carbanions are stabilized by carbonyls, nitriles and aromaticity.
- Pick the most stable conjugate baseCompare anion stability from resonance and electronegativity to pick the weakest base.
- Rank C–H, N–H and O–H acidsOrder acids by atom, hybridization and resonance effects on conjugate-base stability.
Calculate 8
- How far does triethylamine deprotonate acetylacetone?Calculate the equilibrium extent of a proton transfer between equal amounts of an acid and a base from their pKa values.
- How much imidazole is protonated?Calculate the percentage of a base present as its conjugate acid at a given pH from its pKaH.
- Count the cationic carbonsCount the atoms that share a delocalized positive charge in a conjugated cation.
- log K for phenol and methoxideCalculate log K of a proton transfer from the pKa values of the two acids involved.
- Benzoate to benzoic acid ratio at pH 7.2Use the Henderson–Hasselbalch equation to find the ratio of benzoate to benzoic acid in a buffer three units above the pKa.
- log K for acetic acid plus ammoniaCalculate an acid–base equilibrium constant from the pKa values of the two acids.
- Percent of acetic acid ionised at pH 5.76Use the Henderson–Hasselbalch relation to find the ionised fraction of an acid at a given pH.
- log K for phenol and carbonate ionCalculate log K for phenol reacting with carbonate ion from the pKa values of phenol and bicarbonate.
Find the error 2
- Fix a resonance arrowDiagnose a curved arrow drawn from a positive charge and replace it with an electron-pair arrow.
- Does acetic acid make HCl from sodium chloride?Diagnose a wrongly predicted acid–base equilibrium by comparing the strengths of the acids on each side.
Interpret the evidence 2
- What the α-hydrogen pKa values sayInterpret pKa data for carbonyl compounds in terms of competing resonance donation into the carbonyl.
- What cyclohexanol, phenol and a carboxylic acid pKa sayInterpret the pKa values of cyclohexanol, phenol and cyclohexanecarboxylic acid in terms of where resonance places the negative charge.
Work backward 2
- Find a pKa from an equilibrium constantWork backwards from a measured proton-transfer equilibrium constant to the pKa of an unknown acid.
- Which acid fizzes with sodium bicarbonate?Work back from CO2 evolution with sodium bicarbonate to the only candidate whose pKa lies below that of carbonic acid.
Plan a synthesis 2
- Choose a solvent for an acetylidePlan a deprotonation by choosing a solvent that is a weaker acid than the substrate.
- Plan an extraction of benzoic acid, phenol and naphthalenePlan the order of aqueous base washes that separates a carboxylic acid, a phenol and a neutral compound by their pKa values.
Explain why 4
- Why is a C–H next to C=O acidic?Explain the acidity of an α-hydrogen by resonance delocalization of the enolate charge onto oxygen.
- Two cyclic polyenes, very different acidityExplain a large acidity difference between two cyclic polyenes by aromaticity of the conjugate base.
- Same group, opposite effectsExplain how a substituent that withdraws inductively but donates by resonance can raise or lower acidity depending on its ring position.
- Why pyrrole is a far weaker base than pyridineExplain the basicity gap between pyrrole and pyridine from where each nitrogen lone pair sits relative to the aromatic π system.
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