TheArtofwritingreasonableorganicmechanismansinchap13有机化学机理书写艺术习题参考答案13

1、ANSWERSTOPROBLEMSINBODYOFCHAPTER1.1.1.Theresonancestructureontherightisbetterbecauseeveryatomhasitsoctet.12H3C=CHhSthesecondstructureishopelesslystrainedallsp2s2Fsp、FIB14Noby-products.C(l-3)andC(6-9)arethekeystonumbering.625MeBrBreakC4-C6,C9-C11,Cl1-012.Afternumberingthemajorproduct,C6andBr25areleft

2、over,somakeabondbetweenthemandcallitthebyproduct.1.5.(a)MakeC4-O12,C6-C11,C9-O12.(b)MakeC8-N10,C9-C13,C12-Br24.BreakO5-C6,C8-C9.1.6.PhC三CHismuchmoreacidicthanBuC=CH.BecausethepKofHOis15,PhC三CHhasapATa23.17.TlieOHismoreacidic(pATau17)thantheCatotheketone(pATa=20).Becausetheby-productofthereactionisH2

3、O,thereisnoneedtobreaktheO-Hbondtogettoproduct,buttheC-Hbondatotheketonemustbebroken.ANSWERSTOPROBLEMSINBODYOFCHAPTER2.2.1.LDAisastrongbase.TwoE2eliminationsgiveanalkyne,whichisdeprotonatedbytheexcessLDAtogiveanalkynylanion.ThisspeciesthenreactswithMelbyailS2process.W-Pr羊,OMe二(z-PN-yj10MeH1:OMeN(z-P

4、r2)MeO-广耳MeO=MeworkupproductH3C亠-ch3workupproduct2.2(a).LDAdeprotonatestheCatotheester,whichaddstothealdehydetogivethealdolproductafterworkup.尸O0一05、Et2.2(b).BuLideprotonatestheCatothenitrile,whichaddstotheketonetogivethealdolproductafterworkup.2.3.Make:C2-C3.Break:noneNotethatbecausetheNaCNiscataly

5、tic,itsatomsarenotincorporatedintotheproduct,andhencethereisnoneedtonumberthem.cat.NaC斗EtOH,H2O # C2iselectrophilic,andC4is.electrophilic!Tomakeabondbetweenthem,C2mustbeturnedintoanucleopliile(umpohmg).Thismustbethepurposeofthe一CN.AldehydesarenotacidicatthecarbonylC,sotheCNcannotsimplydeprotonateC2.

6、Instead,itmustaddtoC2.NowC2isatoanitrile,itismuchmoreacidic,anditcanbedeprotonatedbyexcessCNtogiveanenolate,whichcanaddtoC4Finally,deprotonationofO1andeliminationofCNgivestheobservedproduct. # # # #C2isbothelectrophilicandparticularlyacidic.C5iselectrophilic,andC6hasnoreactivity,sothefirstbondtobema

7、demustbeC2-C5.Therefore,deprotonationofC2givesanucleopliile,wliichcanattackelectropliilicC5togiveanenolateatC6.NowC6isnucleophilic,andintramolecularSN2substitutionatC2givestheproduct.AlthoughC2isatertiaryalkylhalideandisnotnonnallyexpectedtoundergoSN2substitution,thisreactionworksbecauseitisintramol

8、ecular.EtO、CO?EthBr12 # # # #Tliebasedeprotonates01,whichaddstoC9,givingananionthatisdelocalizedoverCIO,C12,C14,andintotheN02groupTheanionthenexpelsS02duct # # #(b)Make:01-P5,C2-Br4.Break:01-C2,Br4-P5. # 01isclearlyanucleophile,andC2isclearlyailelectropliileP5couldbeeitheranucleo

9、pliile(lonepair)oranelectrophile(leavinggroupattached),butbecauseitreactswith01andbecausetheP5-Br4bondbreaks,illtliisreactionitmustbeactingasailelectrophile.Attackof01onP5illSq2fashiondisplacesBr4,wliichcannowattackC2inanadditionreaction.Finally,theN3lonepairisusedtoexpelO1togivetheobservedproduct.P

10、Br22&E2eliminationofHIfromthearyliodidegivesabenzyne,whichcanbeattackedateitherCofthetriplebondtogivetwodifferentproductsE2eliminationofHBrfromthealkenylhalidegivesailalkyneorailallene,neitherofwhichiselectrophilic.TlieonlyreasonbenzyneiselectropliilicisbecauseofthestrainofhavingtwoC(sp)atomsinasix-

11、memberedling.Removethesix-memberedring,andthestraingoesaway.ThefirstsubstitutioninvolvesattackofPhS一onC6C16togiveC6C15(SPh),andthelastinvolvesattackofPhS一onC6Cl(SPh)5togiveCSPh)Theelimination-additionmechanismisruledoutillbothcasesbecauseoftheabsenceofHatomsadjacenttoCl,sothechoicesareaddition-elimi

12、nationorSRN1.Tliefirstreactioninvolvesaveryelectron-poorarene(allthoseinductivelywithdrawingClatoms),soaddition-eliminationisreasonable,althoughS血1isnotunreasonableThelastsubstitution,though,isatanelectron-richarene,soonlySrj1isareasonablepossibility # # First:Last:SPhSPhPhSPhPhPhSSPhPhSSPhSPhPhPhSS

13、PhPhSSPhSPhSPhPliSSPhSPh # # # #2.11.(a)Ailaddition-eliniiiiationmechanismisreasonable. # # #(b)Ailaddition-eliminationmechanismisnotreasonableEliminationofHBrfromthestartingmaterialgivesan # #MeLNC“、COEa,p-unsaturatedketonethatisnowa兀bondelectropliileataCdifferentfromtheonethatoriginallyhadtheBratt

14、achedtoit.TlieonlyreasonablemechanismisSRN1.Initiation:Me丄NCCO2Et # # # +MeH+product #2.13.(a)Zii(Cu)(b)EtO9CEtO9EtO?CRliEtO2OSiR32.14.CH3/CH # # # 2.15.NumberingcorrectlyiskeytothisproblemTlievvTittenproductismissingthefragmentsCOCF3andMsN,soitislikelythattheyareconnectedtooneanotherillaby-product.

15、AllthenumberingintheproductisclearexceptforN&N9,andN10.N8isattachedtoMsinthestartingmaterialandisprobablystillattachedtoitilltheproduct.ButisN9orN10attachedtoC3intheproduct?C3isveryacidic,andwhenitisdeprotonateditbecomesnucleopliilicN9hasafonnalpositivecharge,soN10iselectropliilicTherefore,N10ismost

16、likelyattachedtoC3intheproduct.Make:C3-N10,C4-N&Break:C3-C4,N8-N9.N8deprotonatesC3tomakethelatternucleophilic,anditaddstoN10.TlielonepaironN10isthenusedtoexpelN8fromN9.N8thenconiesbackandaddstoC4,andexpulsionofC3fromC4affordsthetwoproducts # # #oooo # ANSWERSTOPROBLEMSINBODYOFCHAPTER3.3.1.Theby-prod

17、uctisAcOH.ItisimportantinthisproblemtodrawoutthestructureofAc2Oandlabelalltheatoms.Make:C7-C12,O8-C16.Break:C3-C12,C16-O18.O18HOO20Me27 TliefactthatC12-C3breaksandC12-C7makesisasignalthata1,2-alkylshiftoccurs.TliesliiftrequiresthatacarbocationbefonnedatC7,whichcouldbeaccomplishedbycleavingtheC7-O8bo

18、ndBeforetheC7-O8bondcleaves,somethingelsemustattachto08togiveitafonnalpositivecharge.BecauseweneedtomakeanO8-C16bond,thatsometliiiigcouldbeC16TheroleoftheFeCl3istoencouragetheionizationoftheO18-C16bondbycoordinatingto020.(Alternatively,theFeCl3cancoordinateto017,and08canbeacetylatedwithC16byailaddition-eliminationmechanism.)3OSiR3RC0.MeproductWhydowedrawcleavageoftheC7-O8bondconcertedwithmigrationofC12?Ifthetwostepswerenonconcerted,thenaC7carbocationwouldintervene,andother1,2-shiftscouldoccurFo