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