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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