有机中间体1定稿打印

第二章有机中间体与机理,有机反应活性中间体(Reactiveintermediates),第一节.正碳离子(Carbocations),第二节.负碳离子(Carbanions),第三节.自由基(Freeradicals),第四节.碳烯（卡宾）(Carbenes),第五节.氮烯（乃春）(Nitrenes),第六节.苯炔(Benzyne),有机化学反应历程,13.过渡态要用标准格式书写。一步反应的反应机理必须写出过渡态。14.必要时，考虑共振和分子轨道理论,Carbocations(碳阳离子),Thecentralcarbonatominacarbocationiselectrondeficient;ithasonlysixelectronsinitsoutsideenergylevel.,正电荷越分散，越稳定,1.诱导效应:FCH2CH2+CH3CH2+,2.共轭效应,-I,稳;+I,稳,2.1P-共轭效应p95,(Conjugatedeffects)：,二.Therelativestabilitiesofcarbocations：,2.2-P超共轭,共轭体系的数目越多越稳定,参与超共轭的C-H键越多越稳定,北理工01,bcad,中科院01,三.正碳离子的反应活性：与稳定性基本一致,1.RBrSN1水解速率比较,醇：,按E1反应活性由大到小排列：,按E1反应活性由大到小排列：,20,Moresubstitutedalkenesaremorestable.H2C=CH2R-CH=CH2R-CH=CH-RR-CH=CR2R2C=CR2unsub.monosub.disub.1反应取向：查依采夫规则强酸催化下的醇消除是碳正离子历程,AcidCatalyzedDehydrationofSecondaryandtertiaryalcohols,Protonation,establishingofgoodleavinggroup.,Eliminationofwatertoyieldcarbocationinratedeterminingstep.,EliminationofH+fromcarbocationtoyieldalkene.,醇的b消除,protonation,prutnein,eliminationlmnen,主要得双键上烃基取代较多的烯,氢少消氢,Orientationofelimination,E1reactionsfaithfullyfollowZaitsevsrule!Thismeansthatthemajorproductshouldbetheproductthatisthemosthighlysubstituted.E1reactionsdonotrequireananticoplanarorientationofHandX.,E1反应机理,SN1反应机理,慢,慢,快,快,进攻-H,进攻C+,碱性强，升温对E1有利。中性极性溶剂对SN1有利。,E1反应机理和SN1反应机理的比较,4.PinacolRearrangement:NucleophilicRearrangement*p116,anexampleofstabilizationofacarbocationbyanadjacentlonepair.,-H2O,H+,H+,1.Protonationofahydroxylgroup,Mechanismofthepinacolrearrangement,-H2O,2.Eliminationofwatertoyieldtertiarycarbocation.,Resonance-stablizedcarbocation,Deprotonation,a.不对称的取代乙二醇中，质子化,电子云密度大的羟基优先,动力:氧正离子,更稳定,满足八隅体结构,b.迁移亲核性强的基团优先，能提供电子的基团优先,规律：,Phenylgroupmovefirst,Phenylwithelectrondonorgroupmovefirst,Howtodecidewhichwillbemajor?FirstdecidewhichcarbocationismorestableThenconsidertherelativemigratoryaptitudeofthegroupsthatwillundergo1,2-shift.MigratoryaptitudearylalkylusuallyHalkyl,Hydridegenerallymigratesbecauseofthegenerationofamorestablecarbocation,Stereochemistryofmigration:Themigratinggroupretainsconfiguration.Thatmeansmigratinggroupisnevertotallydetached,CH3迁移,环重排,00科大,ThestericchemistryofPinacolRearrangements,Leavi