高等有机化学 第四章 亲电加成反应(2010).ppt

1、1，4章亲电加成反应，2，(1)亲电加成(2)亲核加成(nucleophilic addition) (3)自由基酸，(1)烯烃亲电加成反应过程，5，Mechanism(1)involves prior dissociation of the electro phile and implies that a carb ocation is generated that is freectro，(1)prior dissociation of electro phile and formation of carb ocation intermediate，6，(2)formation of ca

2、rb ocation ion ppoint，7，mechanism(2)also involves a carb ocation internet But it is generated in the presence of an anion and exists initially as an ion paaan，8，(3)formation a bridged carbonic intermediate from alkene and electro phile。9，Mechanism(3)leads to a bridged intermediate that undergoes add

3、ition by a second step in which the ring is opened by a nu Cleo phile、mechanisms (1)、(2)和(3)are all ade 2 reactions 3360 they are bi molecular er(4)concerted addition of electular.12，碳正离子过程，v=k isopropeneHCl，(2)双分子过程，13，结构稳定的碳正离子中间体生成，碳正离子离子中间体的AdE2过程条件，叔碳正离子中间体，苄基碳正离子，14，钚离子过程In a three-membered ri

4、ng？In 1937，two Columbia chemists proposed just such a species as an intermediate in the reaction of ethylene with bromine . they were right.br2，I2，in3，rscl或ar SCL，Hg (ococh 3) 2，亲电试剂的原子半径必须足够大。为什么形成溴离子而不是碳正离子？哪些亲电试剂和烯烃能形成钚离子中间体？19，钨离子存在的直接证据？biadamantylidene bronomium，20，(3) 3分子历史(AdE3)，部分郑智薰共轭烯烃和HX

5、相加根据AdE3历史进行。立体化学通常是反转相加，21，complex，22，23，2。烯烃亲电加成反应的立体化学，(1)反转加成，24，Ade2:环状，半加成，28，(2)纯加成，碳双键和苯基共轭烯烃和HX的加成反应主要是纯加成，29，Ion pair，30，对比立体选择性，31，顺式加成，p，硼烷和烯烃加成是纯化性，32，(3例如，溴和半-1-苯基丙烯反应得到的半顺式加成物的比例为88336012)。当双键碳原子相连的苯中存在电子团时，纯食加成物的比例也明显提高。，34，反式加成物(88%)，反式加成物(12%)，35，反式加成物(63%)，反式加成物(37%)，36，(35%)，()，4

6、3，44，3。烯烃亲电子添加反应的活性，(1)烯烃结构对添加速度的影响，45，结论：z是推电子基础，双键电子云密度增加。稳定碳正离子中间体，降低活化能，46，结论：Z吸收电子，降低双键电子云密度。碳正离子中间体变得更不稳定，增加活化能，当47，Z强烈吸收电子时，烯烃不会发生亲电加成反应，会发生亲核加成反应！48，49，(2)亲电药对加成率的影响，特定烯烃的卤化氢加成率与酸性强弱一致。HI HBr HCl HF，对于特定烯烃，混合卤素的加成速度与双列难度匹配，ICl IBr I2，50，4。烯烃亲电加成反应的方向性规律，区域选择性影响因素：电子效应，空间效应。51，(1)电子效应，52，“马尔科

7、维科夫规则”？“以碳正离子为中心的-CC单键旋转，带正电荷碳原子的P轨道轴和-CH键的轨道轴在同一平面上时，两个牙齿轨道部分重叠，将部分正电荷分布在甲基上，起到稳定碳正离子的作用，这称为草轭作用。”，53，电磁场强的烯烃和不对称的亲电药相加，表面上是反马尔可夫规则。54，也适用于添加苯乙烯类和卤代烃等不对称试剂的区域选择性，当苯环连接有强吸力电子时，其区域选择性类似于吸入电子和双键碳原子直接连接时。，55，(2)立体效果，56，2，乙炔，丙烯类亲电加成反应，1。alkin的亲电印象，57，Since Alkynes Have type Orbitals，It is not surprising

8、 that there is a good deal of similarity to the reactivity of alkenesthe fundamental questions about additions to alkynes include the following : how reactive are alkynes in comparison with alkenes？what is the stereo chemistry of additions to alkynes？58，what is the regio chemistry of additions to al

9、kynes？the important role of bridged ions in addition reactions of alkenes raises the question of whether similar species are involved with alkynes，whh，59，The basic mechansims that are considered to be involved in electrophilic additions to alkynes 3360，vinyl cation，syn anti，63，mechanism d is a ter m

10、olecular process that would be expected to be a stereo specific anti addition。a DE3，64，ii Alkynes are some what less reactive than alkenes toward many electro philes . a major reason for this difference in reactivity，reactivity，65，For additions that proceed through bridged intermediates，the alkynes are also less reactive because of additions；alkyl-substituted acetyl enes can react with HCl by either the a DE3 or the ade 2 mechanism，Depending on the reactant structure and the reacture，68，anti，The presence of br-grea