4 introduction to organic chemistry Alevel考试化学课件.pptx

Organisingorganicreactions

acid-basereactions.Forexample,ethanoicacidbehavesasatypicalacid,formingsaltswhenreactedwithalkalissuchasaqueoussodiumhydroxide:CH3COOH(aq)+NaOH(aq)→CH3COONa(aq)+H2O(l)Aswithotheracid-basereactions,asaltandwaterareformed.

Reduction–oxidation(redox)reactionsCH3CH2OH(aq)+O2(aq)→CH3COOH(aq)+H2O(l)Inthisredoxreaction,oxygenisreducedtowater.

SubstitutionSubstitutioninvolvesreplacinganatom(oragroupofatoms)byanotheratom(oragroupofatoms).Forexample,thebromineatominbromoethaneissubstitutedbythe–OHgrouptoformethanolonwarmingwithaqueoussodiumhydroxide:CH3CH2Br(l)+OH-(aq)→CH3CH2OH(aq)+Br-(aq)

AdditionreactionAdditionreactionsinvolvetwomoleculesjoiningtogethertoformasinglenewmolecule.Ifetheneandsteamarepassedoverahotphosphoricacidcatalyst,ethonalisproduced:CH2=CH2(g)+H2O→CH3CH3OH(g)

EliminationEliminationinvolvestheremovalofamoleculefromalargeone.Theadditionofethenetosteammaybereversedbypassingethonalvapouroverahotcatalystsuchaspumice.Awatermoleculeiseliminated.CH3CH2OH(g)→CH2=CH2(g)+H2O(g)

HydrolysisreactionsHydrolysisreactionsinvolvebreakingcovalentbondsbyreactionwithwater.Thesubstitutionofthebromineatominbromoethanebyhydrolysisisalsoahydrolysis.Thereactionproceedsmuchmoreslowlyinwater.CH3CH2Br(l)+H2O(l)→CH3CH2OH(aq)+HBr(aq)

Whatisareactionmechanism?Themechanismisdescribedusingequationsforthestepsinvolved.Youwillmeetthefollowingorganicmechanismsinthisbook:Free-radicalsubstitutionElectrophilicadditionNucleophilicsubstitutionElectrophilicsubstitutionNucleophilicadditionThetermsfreeradical,electrophilicandnucleophilicrefertothenatureoftheattackingspeciesinthereaction.

electrophileAnelectrophileisanelectron-pairacceptorwhichisattractedto