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OrganicChemistry,6thEdition

L.G.Wade,Jr.Chapter1

StructureandBondingAcidsandBasesYunfengChenSchoolofChemicalEngineering&PharmacyAtomicStructureprotons,neutrons,andelectronsisotopesAtomicOrbitals2sorbital(spherical)2porbitalElectronicConfigurationsAufbauprinciple:electronsoccupytheorbitalswiththelowestenergyfirstHund’srule:electronswilloccupyemptydegeneratedorbitalsbeforepairingupinthesameorbitalPauliprinciple:onlytwoelectronscanoccupyoneatomicorbitalandthetwoelectronshaveoppositespin.ElectronicConfigurationsoftheElementsoftheFirstandSecondRowsBondFormationIonicbonding:electronsaretransferred.Covalentbonding:electronpairisshared.LewisStructuresBondingelectronsNonbondingelectronsorlonepairsSatisfytheoctetrule!

Practice:writetheLewisstructuresforthebelowmoleculesMultipleBondingDipoleMomentAmountofelectricalchargexbondlength.Chargeseparationshownbyelectrostaticpotentialmap(EPM).Redindicatesapartiallynegativeregionandblueindicatesapartiallypositiveregion.

ElectronegativityandBondPolarityGreaterENmeansgreaterpolarityCalculatingFormalChargeForeachatominavalidLewisstructureCountthenumberofvalenceelectronsSubtractallitsnonbondingelectronsSubtracthalfofitsbondingelectronsIonicStructuresChemicalFormulasFullstructuralformula(nolonepairsshown)Line-angleformulaCondensedstructuralformulaMolecularformulaEmpiricalformulaCH3COOHC2H4O2CH2O

ResonanceOnlyelectronscanbemoved(usuallylonepairsorpielectrons).Nucleipositionsandbondanglesremainthesame.Thenumberofunpairedelectronsremainsthesame.Resonancecausesadelocalizationofelectricalcharge.ResonanceExampleTherealstructureisaresonancehybrid.Allthebondlengthsarethesame.Eachoxygenhasa-1/3electricalcharge.

MajorResonanceFormhasasmanyoctetsaspossible.hasasmanybondsaspossible.hasthenegativechargeonthemostelectronegativeatom.hasaslittlechargeseparationaspossible.MajorContributor?majorminor,

carbondoesnothaveoctet.ResonanceDelocalizationofthenegativechargeontheconjugatebasewillstabilizetheanion,sothesubstanceisastrongeracid.Moreresonancestructuresusuallymeangreaterstabilization.Practice:

ArrheniusAcidsandBasesAcidsdissociateinwatertogiveH3O+ions.BasesdissociateinwatertogiveOH-ions.Kw=[H3O+][OH-]=1.0x10-14at24°CpH=-log[H3O+]Strongacidsandbasesare100%dissociated.Brønsted–LowryAcidsandBasesAciddonatesaprotonBaseacceptsaproton

Strongreactstogiveweak

Theweakerthebase,thestrongerisitsconjugateacid

Stablebasesareweakbases1Conjugateacid-basepairs.AnAcid/BaseEquilibriumKa:

Theaciddissociationconstant1AcidandBaseStrengthAciddissociationconstant,KaBasedissociationconstant,KbForconjugatepairs,(Ka)(Kb)=KwSpontaneousacid-basereactionsproceedfromstrongertoweaker.pKa4.74pKb3.36pKb9.26pKa10.64DeterminingRelativeAcidityElectronegativitySizeResonancestabilizationofconjugatebase

ElectronegativityAsthebondtoHbecomesmorepolarized,Hbecomesmorepositiveandthebondiseasiertobreak.SizeAssizeincreases,theHismorelooselyheldandthebondiseasiertobreak.Alargersizealsostabilizestheanion.

Whenatomsaresimilarinsize,thestrongeracidwillhaveitsprotonattachedtothemoreelectronegativeatom

Inductiveelectronwithdrawalincreasestheacidityofaconjugateacid1AceticacidismoreacidicthanethanolThedelocalizedelectronsinaceticacidaresharedbymorethantwoatoms,therebystabilizingtheconjugatedbase1LewisAcidsandBasesAcidsacceptelectronpairs=electrophileBasesdonateelectronpairs=nucleophilenucleophileelectrophile

Lewisacid:non-proton-donatingacid;willaccepttwoelectrons

Lewisbase:electronpairdonors

Mostoforganicreactionscanbeconsideredasacid-basereaction,thecurveisveryimportantforreactionmechanism.Keepinmind(curve)1Practices:1.Ammonia,haspKa=36andacetonehaspKa=19.Willthefollowingreactiontakeplace?Explain.2.I