Chapter 16 The Chemistry of Benzene Deriva4ves Organic Chemistry, 5th ed. Marc Loudon Eric J. Kantorowski California Polytechnic State University San Luis Obispo, CA
Chapter16TheChemistryofBenzeneDeriva4ves
Organic Chemistry, 5th ed. Marc Loudon
Eric J. Kantorowski California Polytechnic State University San Luis Obispo, CA
Chapter16Overview
• 16.1NomenclatureofBenzeneDeriva6ves
• 16.2PhysicalProper6esofBenzeneDeriva6ves• 16.3SpectroscopyofBenzeneDeriva6ves• 16.4ElectrophilicAroma6cSubs6tu6onReac6onsofBenzene• 16.5ElectrophilicAroma6cSubs6tu6onReac6onsof
Subs6tutedBenzenes
• 16.6Hydrogena6onofBenzeneDeriva6ves• 16.7SourceandIndustrialUseofAroma6cHydrocarbons
2
Nomenclature
• Subs6tu6venomenclature
• Notetheresonancehybridsforthe–NO2group
316.1NomenclatureofBenzeneDeriva4ves
Nomenclature
• Commonnames
• Ortho,meta,andparaprefixes
416.1NomenclatureofBenzeneDeriva4ves
Nomenclature
• Principlegroups
• Othercommonnames
516.1NomenclatureofBenzeneDeriva4ves
Nomenclature
• Numbersarerequiredwhenmorethantwosubs6tuentsarepresent
616.1NomenclatureofBenzeneDeriva4ves
Nomenclature
• Thebenzeneringmayalsobeasubs6tuent
• Thephenylgroup=C6H5‐=Ph‐
• Thebenzylgroup=C6H5CH2‐
716.1NomenclatureofBenzeneDeriva4ves
PhysicalProper<es
• Benzenederiva6vesandhydrocarbonshavesimilarboilingpoints
• Notehowthemel6ngpointsofthehighlysymmetricalcompoundsareunusuallyhigh
816.2PhysicalProper4esofBenzeneDeriva4ves
PhysicalProper<es
• Para‐disubs6tutedderiva6vestypicallyhavemp’shigherthanthoseoforthoandmeta
• Benzeneandotheraroma6chydrocarbonderiva6vesareinsolubleinwater
• IfH‐bondingispossible,thenwatersolubilityisimproved(e.g.,phenol,PhOH)
916.2PhysicalProper4esofBenzeneDeriva4ves
IRSpectroscopy
1016.3SpectroscopyofBenzeneDeriva4ves
1HNMRSpectroscopy
• Benzene:δ 7.4• Mostbenzenederiva6ves:δ 7.0‐8.0
• Ifanunknowncompoundhasanunsatura6onnumberof≥4,immediatelycheckthisregion
• Note:Vinylprotonsofalkenesareatδ 5.0‐5.7
• Whydobenzenederiva6vesappearmoredownfield?
1116.3SpectroscopyofBenzeneDeriva4ves
RingCurrentinNMRSpectroscopy
1216.3SpectroscopyofBenzeneDeriva4ves
RingCurrentinNMRSpectroscopy
• Ringcurrentisbelievedtobethebestexperimentalevidenceofaroma6ccharacter
• Outerprotons:9.28ppm
• Innerprotons:‐2.99ppm(!)
1316.3SpectroscopyofBenzeneDeriva4ves
1HNMRSpectroscopy
• Benzylicprotonsalsoexperienceadownfieldshidrela6vetoordinaryalkylabsorp6ons
• The‐OHabsorp6oninphenolsistypicallyhigher(δ5‐6)thanthatofalcohols(δ2‐3)
1416.3SpectroscopyofBenzeneDeriva4ves
CouplingConstantsofAroma<cProtons
1516.3SpectroscopyofBenzeneDeriva4ves
Para‐Subs<tutedBenzenes
• Apairof“leaningdoublets”withalargeorthocouplingischaracteris6c
1616.3SpectroscopyofBenzeneDeriva4ves
13CNMRSpectroscopy
• Benzene:δ 128.5• Mostbenzenederiva6ves:δ 110‐160
• Benzyliccarbons:δ 18‐30
• RecallthatcarbonsthatdonotbearHsareconsiderablysmallerinsize
1716.3SpectroscopyofBenzeneDeriva4ves
UV‐VisSpectroscopy
• Aroma6chydrocarbonstypicallyhavetwobands:210nm(strong),260(weak)
• Subs6tuentscanalterboththeλmaxvaluesandtheintensi6es
• Thisismorepronouncedwhenthesubs6tuentcanextendconjuga6onofthering
1816.3SpectroscopyofBenzeneDeriva4ves
UV‐VisSpectroscopy
1916.3SpectroscopyofBenzeneDeriva4ves
ElectrophilicAroma<cSubs<tu<on
• Ahydrogenofanaroma6cringisreplacedbyanelectrophile
• Allelectrophilicaroma4csubs4tu4onreac4onsoccurbysimilarmechanisms
2016.4ElectrophilicAroma4cSubs4tu4onReac4onsofBenzene
Halogena<onofBenzene
• Comparewiththeaddi4onproductforthatofanalkene
2116.4ElectrophilicAroma4cSubs4tu4onReac4onsofBenzene
MechanismofHalogena<on
2216.4ElectrophilicAroma4cSubs4tu4onReac4onsofBenzene
MechanismofHalogena<on
2316.4ElectrophilicAroma4cSubs4tu4onReac4onsofBenzene
ThreeMechanis<cStepsinEAS
1.Genera6onofanelectrophile2.Nucleophilicreac6onoftheπelectronsofthearoma6cringwiththeelectrophile
3.Lossofaprotonfromthecarboca6ontoformasubs6tutedaroma6ccompound
2416.4ElectrophilicAroma4cSubs4tu4onReac4onsofBenzene
Nitra<onofBenzene
• Mechanism:
2516.4ElectrophilicAroma4cSubs4tu4onReac4onsofBenzene
Nitra<onofBenzene
2616.4ElectrophilicAroma4cSubs4tu4onReac4onsofBenzene
Sulfona<onofBenzene
• Mechanism:
2716.4ElectrophilicAroma4cSubs4tu4onReac4onsofBenzene
Friedel‐CraMsAlkyla<onofBenzene
• Mechanism:
2816.4ElectrophilicAroma4cSubs4tu4onReac4onsofBenzene
Friedel‐CraMsAlkyla<onofBenzene
• ComparetheroleofAlCl3withthatofFeBr3inthebromina6onreac6on
2916.4ElectrophilicAroma4cSubs4tu4onReac4onsofBenzene
RearrangementsinFriedel‐CraMsAlkyla<ons
• Stablecarboca6onsdonotrearrange
3016.4ElectrophilicAroma4cSubs4tu4onReac4onsofBenzene
Overalkyla<oninFriedel‐CraMsAlkyla<ons
• Thealkylbenzeneproductsaretypicallymorereac4vethanbenzeneitself
• Alargeexcessofbenzenecanminimizethisproblem
3116.4ElectrophilicAroma4cSubs4tu4onReac4onsofBenzene
Friedel‐CraMsAlkyla<ons
• Alkenesandalcoholscanalsobeusedasalkyla6ngreagents
3216.4ElectrophilicAroma4cSubs4tu4onReac4onsofBenzene
Friedel‐CraMsAcyla<onofBenzene
• Theacylgroupistypicallyderivedfromanacidchloride
3316.4ElectrophilicAroma4cSubs4tu4onReac4onsofBenzene
Friedel‐CraMsAcyla<onofBenzene
• Mechanism:
3416.4ElectrophilicAroma4cSubs4tu4onReac4onsofBenzene
Friedel‐CraMsAcyla<onofBenzene
• Incontrasttothealkyla6onversion,oneequivalentofAlCl3isrequired
3516.4ElectrophilicAroma4cSubs4tu4onReac4onsofBenzene
IntramolecularFriedel‐CraMsReac<ons
• Boththealkyla6onandacyla6onscanoccurintramolecularly
• Thereac6onoccursatanorthoposi6onandisbestforfive‐andsix‐memberedrings
3616.4ElectrophilicAroma4cSubs4tu4onReac4onsofBenzene
Direc<ngEffectsofSubs<tuents
• Regioselec6vityisobservedinEASreac6onsonmonosubs6tutedbenzenerings
• Ortho,para‐direc6ng:
• Meta‐direc6ng:
3716.5ElectrophilicAroma4cSubs4tu4onReac4onsofSubs4tutedBenzenes
Direc<ngandAc<va<ngEffects
3816.5ElectrophilicAroma4cSubs4tu4onReac4onsofSubs4tutedBenzenes
Ortho,Para‐Direc<ngGroups
• Alkylgroups• Groupsthathaveunsharedelectronpairsonatomsdirectlyakachedtothebenzenering
3916.5ElectrophilicAroma4cSubs4tu4onReac4onsofSubs4tutedBenzenes
Ortho,Para‐Direc<ngGroups
• Thechargeonthemeta‐derivedintermediatecannotbedelocalizedontothe‐OCH3group
4016.5ElectrophilicAroma4cSubs4tu4onReac4onsofSubs4tutedBenzenes
Ortho,Para‐Direc<ngGroups
4116.5ElectrophilicAroma4cSubs4tu4onReac4onsofSubs4tutedBenzenes
Ortho,Para‐Direc<ngGroups
• Alkylsubs6tutedbenzeneringshaveasimilarexplana6on
4216.5ElectrophilicAroma4cSubs4tu4onReac4onsofSubs4tutedBenzenes
TheOrtho,ParaRa<o
• Rarelydoo,p‐directorsprovidetwiceasmuchorthoproductasparaproduct
• Typicallyparapredominatesoverortho
• Some6mesthisisduetospa6aldemands,butmanycasesarelesseasilyexplained
• Fortunately,orthoandparaproductshavedifferentphysicalproper6esandcanbeseparated
4316.5ElectrophilicAroma4cSubs4tu4onReac4onsofSubs4tutedBenzenes
Meta‐Direc<ngGroups
• Groupsthathaveposi6vechargesadjacenttothebenzenering
• Groupsthathavebonddipoleswithapar6alposi6vechargeadjacenttothebenzenering
4416.5ElectrophilicAroma4cSubs4tu4onReac4onsofSubs4tutedBenzenes
Meta‐Direc<ngGroups
4516.5ElectrophilicAroma4cSubs4tu4onReac4onsofSubs4tutedBenzenes
Meta‐Direc<ngGroups
4616.5ElectrophilicAroma4cSubs4tu4onReac4onsofSubs4tutedBenzenes
Ac<va<ngandDeac<va<ngEffects
• Ac<va<nggroup:Agroupthatallowsthederiva6vetoreactmorerapidlythanbenzene
• Deac<va<nggroup:Agroupthatcausesthederiva6vetoreactmoreslowlythanbenzene
1.Allmeta‐directorsaredeac6va6ng
2.Allortho,para‐directorsareac6va6ng
3.Halogensaredeac6va6ng
4716.5ElectrophilicAroma4cSubs4tu4onReac4onsofSubs4tutedBenzenes
Ac<va<ngandDeac<va<ngEffects
• Controlledbytwosimultaneouslyopera4ngproper6esofsubs6tuents
• Resonanceeffect:
• Polareffect:
4816.5ElectrophilicAroma4cSubs4tu4onReac4onsofSubs4tutedBenzenes
Ac<va<ngandDeac<va<ngEffects
4916.5ElectrophilicAroma4cSubs4tu4onReac4onsofSubs4tutedBenzenes
Ac<va<ngandDeac<va<ngEffects
• Orbitaloverlapmayalsoaffectthedegreetowhichtheresonanceeffectoperates
5016.5ElectrophilicAroma4cSubs4tu4onReac4onsofSubs4tutedBenzenes
UseofEASinOrganicSynthesis
• Withtwoormoresubs6tuents,theac6va6nganddirec6ngeffectsareroughlythesumoftheeffectsoftheindividualsubs6tuents
5116.5ElectrophilicAroma4cSubs4tu4onReac4onsofSubs4tutedBenzenes
UseofEASinOrganicSynthesis
5216.5ElectrophilicAroma4cSubs4tu4onReac4onsofSubs4tutedBenzenes
UseofEASinOrganicSynthesis
• SomeEASreac6onscanbecarriedoutunderverymildcondi6onsandwithoutacatalyst
5316.5ElectrophilicAroma4cSubs4tu4onReac4onsofSubs4tutedBenzenes
UseofEASinOrganicSynthesis
5416.5ElectrophilicAroma4cSubs4tu4onReac4onsofSubs4tutedBenzenes
Hydrogena<on
• Aroma6cringsareresistanttohydrogena6on
• Moreextremecondi6onsaregenerallyrequired(higherTand/orP)
5516.6Hydrogena4onofBenzeneDeriva4ves
Hydrogena<on
• Thereac6oncannotbeselec6velystopped
5616.6Hydrogena4onofBenzeneDeriva4ves
Aroma<cHydrocarbons
• Themostcommonsourceofaroma6chydrocarbonsispetroleum
• Coaltarisanotherpoten6allyimportant,butcurrentlyminorsource
• Benzeneistheprinciplesourceofstyrene,ethylbenzene,andcumene
5716.7SourceandIndustrialUseofAroma4cHydrocarbons
Aroma<cHydrocarbons
• Xylenesarealsoobtainedfrompetroleum• Para‐xyleneisthemostimportantofthese
• Virtuallytheen6reproduc6onofp‐xyleneisusedforprepara6onofterephthalicacid
• Terephthalicacidisusedinpolyestersynthesis
5816.7SourceandIndustrialUseofAroma4cHydrocarbons