亲核试剂和亲电试剂

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1、=>NucleophilesandelectrophilesNucleophiles---Nu-(亲核试剂)Electron-richmoleculesarecallednucleophiles(meaningnucleusloving)OH-Nucleophiliccenter(亲核中心)NucleophileshaveaspecificatomorregionofthemoleculewhichiselectronrichElectrophiles(亲电试剂)Electron-deficientmoleculesarecalledelectrophiles(elect

2、ron-loving)andreactwithnucleophiles.CH3+（CH3Cl）Electrophiliccenter(亲电中心)Electrophileshaveaspecificatomorregionofthemoleculewhichiselectrondeficient.Thisregioniscalledtheelectrophiliccenter.Anions（阴离子）Anegativelychargedmoleculesuchasthehydroxideioniselectronrichandactsasanucleophile.Theato

3、mwhichbearsthenegativechargeandalonepairofelectronsisthenucleophiliccenter,whichinthecaseofthehydroxideionistheoxygenatomSomeions(e.g.thecarboxylateion)areabletosharethenegativechargebetweentwoormoreatomsthroughaprocessknownasdelocalization.Inthiscase,thenegativechargeissharedbetweenbotho

4、xygenatomsandsobothoftheseatomsarenucleophiliccentersnucleophiliccentersCations（阳离子）Apositivelychargedioniselectrondeficientandactsasanelectrophile.Theatomwhichbearsthepositivechargeistheelectrophiliccenter.Thisisthecarbonatom.Carbocation(碳正离子）Somemolecules(e.g.theallyliccation)areabletod

5、elocalizetheirpositivechargebetweentwoormoreatomsinwhichcasealltheatomscapableofsharingthechargeareelectrophiliccenterselectrophiliccentersallyliccation.Polarbonds（极性键）Iftwoatomsofquitedifferentelectronegativitiesarelinkedtogether,thenthebondconnectingthemwillbepolarcovalent（极性共价键）suchtha

6、tthebondingelectronsarebiasedtowardsthemoreelectronegativeatom.Thiswillgivethelatteraslightlynegativechargeandmakeitanucleophiliccenter.Conversely,thelesselectronegativeatomwillgainaslightlypositivechargeandbeanelectrophiliccenterRelativenucleophilicityInaseriesofanions,nucleophilicstreng

7、thparallelsbasicityifthenucleophiliccenteristhesameatom.nucleophilicstrengthbasicitystrengthR3C->R2N->RO->F-)nucleophilicstrengthbasicitystrengthRO->HO->>RCO2-Themoreelectronegativetheatom(e.g.F),themoretightlyitholdsontoitselectronsandthelessavailabletheseelectrons