an aldol condensation reaction the synthesis of - academic：一种羟醛缩合反应合成-学术

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1、AnAldolCondensationReaction:TheSynthesisofTetraphenylcyclopentadienone—AnExampleofaDouble-CrossedAldolAdditionReactionsofCarbonylGroupsThechemicalreactivityofaldehydesandketonesiscloselyassociatedwiththepresenceofthecarbonylgroupintheirstructures.Forexample,bothaldehydesandketonesundergoadditio

2、nreactionssuchastheadditionofaGrignardreagenttothecarbonylgroupasshowninFigure1.Figure1.Additionreactions.ThereactionsinFigure1differonlybecausethepinkHofanaldehydeisreplacedbyR′′intheketone.Theadditionreactionoccursatthecarbonylgroup.Thecarbonylgroupispolarizedsothatthecarbonatombearsapartialp

3、ositivechargeandtheoxygenatombearsapartialnegativecharge.TheR′groupoftheGrignardreagentisnegativerelativetothepositiveMgatom.Thus,thenegativeR′groupbondstothepositivecarbonatom,andthenegativeoxygenandmetallicmagnesiumformanionicbond,yieldingasaltineachreaction.Theadditionproductisacidifiedineac

4、hcasetomakeacovalentalcohol.ThealdehydeproducesaIIoalcohol;whereas,theketoneproducesaIIIoalcoholowingtotheR′′group.ThetwoequationsforadditionreactionsinFigure1aresummarizedinFigure2.Anucleophile(negativespecies)bondstothecarbonylcarbon(positive),breakingthepbondofthecarbonylgroup.11Lab12Figure2

5、.Additionofanucleophiletoacarbonylgroup.Figure2focusesourattentiononthesalientpartofanadditionreactionthatinvolveseitheraketoneoranaldehyde.Anucleophilebondstothecarbonylcarbon.Inanaldoladditionreaction,thenucleophileisanenolateformedfromanaldehydeorketonebytheremovalofahydrogenatomnexttothecar

6、bonylgroup.Theenolate(negativenucleophile)thenaddstoacarbonylgroupofanotheraldehydeorketoneasshowninFigure1.FormationofanEnolatefromanAldehydeorKetoneAldehydesandketonesthatpossessalphahydrogenatomscanformenolates.TheGreekalphabet(a,b,g,etc.)isusedbychemiststoidentifycarbonatomsinrelationtothec

7、arbonatomofacarbonylgroup.Analphacarbonatomisacarbonatomthatisbondeddirectlytothecarbonatomofacarbonylgroup.Abetacarbonatomisthesecondcarbonatomfromthecarbonylcarbon,agammacarbonisthethirdcarbonawayfromthecarbonyl,etc.Likewise,hyd