Download - Chapter 19 19 Overview • 19.11 Reacons of Aldehydes and Ketones with Amines • 19.12 Reducon of Carbonyl Groups

Chapter19TheChemistryofAldehydesandKetones.

Carbonyl‐Addi7onReac7ons

Organic Chemistry, 5th ed. Marc Loudon

Eric J. Kantorowski California Polytechnic State University San Luis Obispo, CA

Chapter19Overview

•  19.1NomenclatureofAldehydesandKetones

•  19.2PhysicalProper;esofAldehydesandKetones•  19.3SpectroscopyofAldehydesandKetones•  19.4SynthesisofAldehydesandKetones•  19.5Introduc;ontoAldehydeandKetoneReac;ons•  19.6BasicityofAldehydesandKetones•  19.7ReversibleAddi;onReac;onsofAldehydesandKetones•  19.8Reduc;onofAldehydesandKetonestoAlcohols•  19.9Reac;onsofAldehydesandKetoneswithGrignardand

RelatedReagents

•  19.10AcetalsandTheirUseofProtec;ngGroups

2

Chapter19Overview

•  19.11Reac;onsofAldehydesandKetoneswithAmines

•  19.12Reduc;onofCarbonylGroupstoMethyleneGroups•  19.13TheWiQgAlkeneSynthesis

•  19.14Oxida;onofAldehydestoCarboxylicAcids•  19.15ManufactureandUseofAldehydesandKetones

3

CarbonylCompounds

•  Aldehydesandketoneshavethefollowinggeneralstructure

419.1NomenclatureofAldehydesandKetones

CarbonylCompounds


CommonNomenclature


PrefixesUsedinCommonNomenclature


CommonNomenclature


Subs?tu?veNomenclature


PhysicalProper?es

•  Mostsimplealdehydesandketonesareliquids

1119.2PhysicalProper7esofAldehydesandKetones

IRSpectroscopy

•  StrongC=Ostretch:1700cm‐1

1219.3SpectroscopyofAldehydesandKetones

IRSpectroscopy

•  Conjuga;onwithaπbondlowerstheabsorp;onfrequency


IRSpectroscopy

•  TheC=Ostretchingfrequencyinsmall‐ringketonesisaffectedbyringsize


1HNMRSpectroscopy

•  Thereasonforthelargeδvalueforaldehydicprotonsissimilartothatforvinylicprotons

•  However,theelectronega;veOincreasesthisshi^fartherdownfield


13CNMRSpectroscopy

•  AldehydeandketoneC=O:δ190‐220•  α‐Carbons:δ30‐50


UV/VisSpectroscopy

•  π→π*:150nm(outoftheopera;ngrange)•  n→π*:260‐290nm(muchweaker)


UV/VisSpectroscopy


MassSpectrometry


MassSpectrometry

•  Whataccountsforthem/z=58peak?


MassSpectrometry

•  TheMcLaffertyrearrangementinvolvesahydrogentransferviaatransientsix‐memberedring

•  Theremustbeanavailableγ‐H


SummaryofAldehydeandKetonePrepara?on

1.Oxida;onofalcohols2.Friedel‐Cra^sacyla;on

3.Hydra;onofalkynes

4.Hydrobora;on‐oxida;onofalkynes

5.Ozonolysisofalkenes

6.Periodatecleavageofglycols

2219.4SynthesisofAldehydesandKetones

Carbonyl‐GroupReac?ons

•  Reac;onswithacids

•  Addi;onreac;ons

•  Oxida;onofaldehydes

2319.5Introduc7ontoAldehydeandKetoneReac7ons

BasicityofAldehydesandKetones

•  Thecarbonyloxygenisweaklybasic

•  Oneresonancecontributorrevealsthatcarboca;oncharacterexists

•  Theconjugateacidsofaldehydesandketonesmaybeviewedasα‐hydroxycarboca;ons

2419.6BasicityofAldehydesandKetones

BasicityofAldehydesandKetones

•  α‐hydroxyandα‐alkoxycarboca;onsaresignificantlymorestablethanordinarycarboca;ons(by~100kJmol‐1)

2519.6BasicityofAldehydesandKetones

Addi?onReac?ons

•  Oneofthemosttypicalreac;onsofaldehydesandketonesisaddi;onacrosstheC=O

2619.7ReversibleAddi7onReac7onsofAldehydesandKetones

MechanismofCarbonyl‐Addi?onReac?ons


Addi?onReac?ons

•  Theaddi;onofanucleophiletothecarbonylcarbonisdrivenbytheabilityofoxygentoaccepttheunsharedelectronpair


Addi?onReac?ons

•  Thenucleophileaiackstheunoccupiedπ*MO(LUMO)oftheC=O


Addi?onReac?ons

•  Thesecondmechanismforcarbonyladdi;ontakesplaceunderacidiccondi7ons


EquilibriainCarbonyl‐Addi?onReac?ons

•  Theequilibriumforareversibleaddi;ondependsstronglyonthestructureofthecarbonylcompound

1.Addi;onismorefavorableforaldehydes

2.Addi;onismorefavorableifENgroupsareneartheC=O

3.Addi;onislessfavorablewhengroupsthatdonateelectronsbyresonancetotheC=Oarepresent


EquilibriumConstantsforHydra?on


Rela?veCarbonylStability


CarbonylStability

•  Anyfeaturethatstabilizescarboca;onswillimpartgreaterstabilitytothecarbonylgroup

•  Forexample,alkylgroupsstabilizecarboca;onsmorethanhydrogens

•  Hence,alkylgroupswilldiscourageaddi;onreac;onstothecarbonylgroup


CarbonylStability

•  Resonancecanalsoaddstabilitytothecarbonylgroup

•  However,ENgroupsmaketheaddi;onreac;onmorefavorable


RatesofCarbonyl‐Addi?onReac?ons

•  Rela;veratescanbepredictedfromequilibriumconstants

•  Compoundswiththemostfavorableaddi;onequilibriatendstoreactmostrapidly

•  Generalreac;vity:formaldehyde>aldehydes>ketones


Reduc?onwithLiAlH4andNaBH4

3719.8Reduc7onofAldehydesandKetonestoAlcohols

Reduc?onwithLiAlH4

•  LiAlH4servesasasourceofhydrideion(H:‐)

•  LiAlH4isverybasicandreactsviolentlywithwater;anhydroussolventsarerequired


Reduc?onwithLiAlH4

•  Likeotherstrongbases,LiAlH4isalsoagoodnucleophile

•  Addi;onally,theLi+ionisabuilt‐inLewis‐acid


Reduc?onwithLiAlH4

•  Eachoftheremaininghydridesbecomeac;vatedduringthereac;on


Reduc?onwithNaBH4

•  Na+isaweakerLewisacidthanLi+requiringtheuseofpro;csolvents

•  Hydrogenbondingthenservestoac;vatethecarbonylgroup


Reduc?onwithLiAlH4andNaBH4

•  Reac;onsbytheseandrelatedreagentsarereferredtoashydridereduc?ons

•  Thesereac;onsarefurtherexamplesofnucleophilicaddi7on


Selec?vitywithLiAlH4andNaBH4

•  NaBH4islessreac;veandhencemoreselec7vethanLiAlH4

•  LiAlH4reactswithalkylhalides,alkyltosylates,andnitrogroups,butNaBH4doesnot


Reduc?onbyCataly?cHydrogena?on

•  Hydridereagentsaremorecommonlyused

•  However,cataly;chydrogena;onisusefulforselec;vereduc;onofalkenes


GrignardAddi?on

•  Grignardreagentswithcarbonylgroupsisthemostimportantapplica;onoftheGrignardreagentinorganicchemistry

4519.9Reac7onsofAldehydesandKetoneswithGrignardandRelatedReagents

GrignardAddi?on

•  R‐MgXreactsasanucleophile;thisgroupisalsostronglybasicbehavinglikeacarbanion

•  Theaddi;onisirreversibleduetothisbasicity


OrganolithiumandAcetylideReagents

•  ThesereagentsreactwithaldehydesandketonesanalogoustoGrignardreagents


ImportanceoftheGrignardAddi?on

•  Thisreac;onresultsinC‐Cbondforma;on

•  Thesynthe;cpossibili;esarealmostendless


ImportanceoftheGrignardAddi?on


Prepara?onandHydrolysisofAcetals

•  Acetal:Acompoundinwhichtwoetheroxygensareboundtothesamecarbon

5019.10AcetalsandTheirUseofProtec7ngGroups


•  Useofa1,2‐or1,3‐diolleadstocyclicacetals•  Onlyoneequivalentofthediolisrequired



•  Acetalforma;onisreversible•  Thepresenceofacidandexcesswaterallowsacetalstoreverttotheircarbonylform

•  Acetalsarestableinbasicandneutralsolu7on


Hemiacetals

•  Hemiacetalsnormallycannotbeisolated•  Excep;onsincludesimplealdehydesandcompoundsthancanform5‐and6‐memberedrings


Hemiacetals


Protec?ngGroups

•  Aprotec?nggroupisatemporarychemicaldisguiseforafunc;onalgrouppreven;ngitfromreac;ngwithcertainreagents


Protec?ngGroups


Reac?onswithPrimaryAmines

•  Iminesaresome;mescalledSchiffbases

5819.11Reac7onsofAldehydesandKetoneswithAmines

Reac?onswithPrimaryAmines

•  Thedehydra;onofwateristypicallytherate‐limi;ngstep


Deriva?ves

•  Beforetheadventofspectroscopy,aldehydesandketoneswerecharacterizedasderiva?ves


SomeImineDeriva?ves


Reac?onswithSecondaryAmines

•  Likeimineforma;on,enamineforma;onisreversible


Reac?onswithSecondaryAmines


Reac?onswithTer?aryAmines

•  Ter;aryaminesdonotreactwithaldehydesorketonestoformstablederiva7ves

•  Theyaregoodnucleophiles,butthelackofanN‐Hpreventsconversiontoastablecompound


Reduc?onofAldehydesandKetones

•  Completereduc;ontoamethylene(‐CH2‐)groupispossiblebytwodifferentmethods

•  Wolff‐Kishnerreduc?on:

6519.12Reduc7onofCarbonylGroupstoMethyleneGroups


•  TheWolff‐Kishnerreduc;ontakesplaceunderhighlybasiccondi7ons

•  Itisanextensionofimineforma;on



•  Clemmensenreduc?on:

•  Thisreduc;onoccursunderacidiccondi7ons•  Themechanismisuncertain


TheWiVgAlkeneSynthesis

•  Thisreac;oniscompletelyregioselec;ve,assuringtheloca;onofthealkene

6819.13TheWiUgAlkeneSynthesis


•  Occursviaanaddi;on‐elimina;onsequenceusingaphosphorousylide

•  Anylid(orylide)isanycompoundwithoppositechargesonadjacent,covalentlyboundatoms


Prepara?onoftheWiVgReagent

•  Anyalkylhalidethatreadilypar;cipatesinSN2reac;onscanbeused



•  Retrosynthe;cally

•  Stereochemistry


CarboxylicAcidsfromAldehydes

•  Thehydrateisthespeciesoxidized

7319.14Oxida7onofAldehydestoCarboxylicAcids

CarboxylicAcidsfromAldehydes

•  ThisisknownastheTollen’stest•  Aposi;veindicatorforanaldehydeisthedeposi;onofametallicsilvermirroronthewallsofthereac;onflask

7419.14Oxida7onofAldehydestoCarboxylicAcids

Produc?onandUseofAldehydes

•  Themostimportantcommercialaldehydeisformaldehyde

•  Itsmostimportantuseisinthesynthesisofphenol‐formaldehyderesins

7519.15ManufactureandUseofAldehydesandKetones

Produc?onandUseofKetones

•  Themostimportantcommercialketoneisacetone

•  Itisco‐producedwithphenolbytheautoxida;on‐rearrangementofcumene

7619.15ManufactureandUseofAldehydesandKetones

Download - Chapter 19 19 Overview • 19.11 Reacons of Aldehydes and Ketones with Amines • 19.12 Reducon of Carbonyl Groups

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