高等有机化学--亲电加成反应.pptx

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,第四章,亲电加成反应,1,1/81,（1）亲电加成(electrophilic addition),（2）亲核加成(nucleophilic addition),（3）自由基加成(radical addition),（4）环加成(cycloaddition),碳碳重键(multiple bonds)加成反应,2,2/81,一、碳-碳双键亲电加成反应,烯烃活泼原因：,电子受核束缚力小，轻易极化。,3,3/81,1.烯烃亲电加成反应历程,4,4/81,Mechanism（1）,involves prior dissociation of the electrophile and implies that a,carbocation,is generated that is free of the counterion,Y,-,at its formation.,（1）,Prior dissociation of electrophile and formation of carbocation intermediate,5,5/81,（2）,Formation of carbocation ion pair from alkene and electrophile.,6,6/81,Mechanism（2）,also involves a carbocation intermediate,but it is generated in the presence of an anion and exists initially as an ion pair.Depending on the mutual reactivity of the two ions,they might or might not become free of one another before combining to give product.,7,7/81,（3）,Formation a bridged carbonic intermediate from alkene and electrophile.,8,8/81,Mechanism（3）,leads to a bridged intermediate that undergoes addition by a second step in which the ring is opened by a nucleophile.Mechanism（3）implies stereospecific anti addition.,Mechanisms（1）,（2）and（3）are all Ad,E,2 reactions:,they are bimolecular electrophilic additions.,9,9/81,（4）,Concerted addition of electrophile and nucleophile in a,termolecular,reaction,10,10/81,Mechanism（4）,is a process that has been observed for several electrophilic additions and implies concerted transfer of the electrophilic and nucleophilic components of the reagent from two separate molecules.,It is a termolecular electrophilic addition,Ad,E,3,a mechanism that implies formation of a complex between one molecule of the reagent and the reactant and also is expected to,result in anti addition.,11,11/81,碳正离子历程,v,=,k,isopropene,HCl,（2）双分子历程,12,12/81,生成结构稳定碳正离子中间体,碳正离子中间体,Ad,E,2历程,条件,叔碳正离子中间体、苄基型碳正离子,13,13/81,通常不含有立体选择性,14,14/81,有时有重排产物出现,重排产物出现可作为经碳正离子,中间体历程证据之一,15,15/81,鎓型离子历程,立体化学为,反式加成,16,16/81,“Bromine with two bonds and a positive charge?In a three-membered ring?In 1937,two Columbia chemists proposed just such a species as an intermediate in the reaction of ethylene with bromine.They were right.”,17,17/81,溴鎓离子含有八隅体结构，碳正离子为六电子体，前者比后者稳定。,Br,2,I,2,IN,3,RSCl or ArSCl,Hg(OCOCH,3,),2,亲电试剂原子半径要足够大,思索：,为何形成溴鎓离子而不是碳正离子？,哪些,亲电试剂与烯烃可形成鎓型离子中间体？,18,18/81,鎓离子存在直接证据？,Biadamantylidene bronomium,19,19/81,（3）三分子历程（,Ad,E,3,）,一些,非共轭烯烃,与,HX,加成按AdE3历程进行。,立体化学通常为,反式加成,20,20/81,complex,21,21/81,22,22/81,2.烯烃亲电加成反应立体化学,（1）反式加成（Antiaddition）,23,23/81,Ad,E,2：包括环状鎓离子形成,反,式,加,成,24,24/81,反式加成,25,25/81,反式加成,26,26/81,Ad,E,3：一分子烯烃和一分子烯烃与HX形成络合物反应。,反式加成,27,27/81,（2）顺式加成（synaddition）,碳碳双键与苯基共轭烯烃,和HX加成反应主要给出顺式加成产物,28,28/81,Ion pair,Owing to the greater stability of the benzylic carbocations formed in these reactions,concerted attack by halide ion is not required for protonation.,29,29/81,对比立体选择性,30,30/81,顺式加成,p,硼烷与烯烃加成为,顺式加成,31,31/81,（3）无立体选择性加成,32,32/81,实例1：,解释双键碳原子上,连有苯基烯烃与溴,加成时，顺式加成产物增多。如：溴与反-1-苯基丙烯反应所得反、顺式加成产物之比为88:12；当双键碳原子所连苯基上有给电子基团时，顺式加成产物百分比也显著升高。,33,33/81,反式,加成产物,（88%）,顺式,加成产物,（12%）,34,34/81,反式,加成产物,（63%）,顺式,加成产物,（37%）,35,35/81,一些芳烃与卤素加成，主要生成顺式加成产物。,（35%）,（10%）,实例2：,36,36/81,提醒：,37,37/81,邻基参加,（注意）,当双键邻位有带未共用电子正确基团存在时，该基团会对碳正离子中间体进行亲核进攻。,38,38/81,比如：,39,39/81,对比：,40,40/81,41,41/81,一些,五、六元环状内酯或环醚,形成也和邻基参加相关。,42,42/81,43,43/81,3.烯烃,亲电加成反应活性,（1）烯烃结构对加成速率影响,44,44/81,结论：,Z为推电子基，使双键电子云密度增加；稳定碳正离子中间体，降低活化能,45,45/81,结论：,Z为吸电子基，使双键电子云密度降低；使碳正离子中间体更不稳定，增加活化能,46,46/81,Z为强吸电子基时,，烯烃不发生亲电加成反应，,发生亲核加成反应！,47,47/81,48,48/81,（2）亲电试剂,对加成速率影响,对于特定烯烃，卤化氢加成速率与酸性强弱一致。,HI HBr HCl HF,对于特定烯烃，混合卤素加成速率与其异裂难易程度相符,ICl IBr I,2,49,49/81,4.烯烃亲电加成反应定向规律,区域选择性影响原因：,电子效应，空间效应。,50,50/81,（1）电子效应,51,51/81,“Markovnikov 规则”？,“围绕碳正离子,-CC单键旋转，当带正电荷碳原子p轨道轴和-CH键轨道轴在同一平面时，,这两个轨道可发生部分重合，,使部分正电荷分散到甲基上，起稳定碳正离子作用，这种现象称超共轭作用”。,52,52/81,对含,强吸电子基团,烯烃与,不对称亲电试剂,加成，从表面上看是反马氏规则。,53,53/81,也适合用于苯乙烯类与卤化氢等不对称试剂加成区域选择性，,且当苯环上连有强吸电子基时，其区域选择性与吸电子基和双键碳原子直接相连时相同。,54,54/81,（2）立体效应,55,55/81,二、炔烃和丙二烯类亲电加成反应,1.,炔烃,亲电加成,56,56/81,Since alkynes have,type orbitals,it is not surprising that there is a good deal of,similarity to the reactivity of alkenes.,The fundamental questions about additions to alkynes include the following:,How reactive,are alkynes in comparison with alkenes?,What is the stereochemistry,of additions to alkynes?,57,57/81,What is the regiochemistry of additions to alkynes?,The important role of bridged ions in addition reactions of alkenes raises the question of whether similar species are involved with alkynes,where the ring includes a double bond and bridged intermediates and would be expected to be substantially more strained.,58,58/81,The,basic mechansims,that are considered to be involved in electrophilic additions to alkynes:,vinyl cation,syn+anti,Ad,E,2,59,59/81,This mechanism,involves a discrete vinyl cation.In general,this reaction will lead to a mixture of the two stereoisomeric addition products.,60,60/81,Bridged intermediate,Bridged intermediate,Ad,E,3,Ad,E,2,61,61/81,Mechanisms B and C,depict bridged intermediates formed without or with participation of a second electrophilic molecule.They should lead to,anti addition.,62,62/81,Mechanism D,is a termolecular process that would be expected to be a,stereospecific anti addition.,Ad,E,3,63,63/81,In general,alkynes are somewhat less reactive than alkenes toward many electrophiles.A major reason for this difference in reactivity is the substantially higer energy of the vinyl cation intermediate that is formed by an electrophilic attack on an alkyne.,Reactivity,64,64/81,For additions that proceed through bridged intermediates,the alkynes are,also less reactive because of additional strain in the intermediate.,Reactivity,65,65/81,Example 1.Hydrohalogenation,Aryl-substituted,acetylenes give mainly the,syn,addition,product.,vinyl cation(as ion pair),66,66/81,Alkyl-substituted acetylenes,can react with HCl by either the,Ad,E,3 or the Ad,E,2,mechanism,depending on the reactant structure and the reaction conditions.The stereochemistry is,anti,addition.,67,67/81,anti,The presence of Br,-,greatly accelerates the reaction,68,68/81,Example 2.Halogenation of alkynes,Disubstituted,(internal),anti,69,69/81,2.,丙二烯类,亲电加成,（注意）,allene,allylic carbocation?,vinyl carbocation,70,70/81,The kinetically favored protonation,at a,sp,2,carbon leads to the vinyl cation intermediate.,The reason is stereoelectronic:the allene structure is nonplanar,so that a,protonation of the center carbon,leads to a twisted structure that,lacks of allylic conjugation.,+,71,71/81,+,中间过程缺乏烯丙基型碳正离子共轭,72,72/81,（1）丙二烯与卤化氢,加成时，主要生成,卤素加到中间碳原子上,产物.,主产物,73,73/81,（2）丙二烯与卤素和汞离子,可形成桥状离子中间体，亲核试剂普通进攻其烯丙位。,74,74/81,3.,共轭二烯,亲电加成反应,75,75/81,1,2-,76,76/81,9.3 共轭二烯亲电加成反应,77,77/81,低温，动力学控制（考查中间体稳定性），主要生成,1,2-,加成产物；,高温，热力学控制（考查产物稳定性），主要生成,1,4,-加成产物。,在一样反应条件下，高温加热两异构体可得相同含量混合物,卤素和共轭多烯加成也可生成各种加成产物,78,78/81,9.4 亲电加成反应在有机合成中应用,形成C,X键、CO键、CN键、,CC,键等,1.C,X,键形成,加,X,2,，HX，HOX,2.C,O,键形成,加,H,2,O，醇，羧酸,3.C,N,键形成,加,NOCl，NO,2,Cl,79,79/81,4.C,C,键形成,加,RX，RCOCl,80,80/81,习题：,（1）比较以下化合物与HCl反应反应活性：,（2）比较以下化合物与Br,2,反应反应活性：,（3）完成以下反应方程式：,81,81/81,