第三章单烯烃(6学时)修改版.ppt

第三章 单烯烃 Chapter 3 Alkenes (6 hours),Classification of Olefines 烯烃的种类,Contents,3.1 Structure of Alkenes 3.2 Isomerism and nomenclature 3.3 Physical properties of alkenes 3.4 Chemical properties of alkenes 3.5 inductive effect 3.6 Mechanism of electrophilic addition 3.7 ethene and propene 3.8 Preparation of alkene 3.9 Fossil oil,Calculating the Degree of Unsaturation（不饱和度）,中文名称: “烯烃的烯意思是少”,Because of its doube bond, an alkene (CnH2n) has fewer hydrogens than an alkane (CnH2n+2)with the same number of carbons, and is therefore referred to as unsaturated., = 1, = 1, = 2,In general, each ring or double bond in a molecule corresponds to a loss of two hydrogens from the alkane formula (CnH2n+2) The degree of unsaturation-the number of rings and /or mutiple bonds present in the molecule.,1 ring,1 ring 1 C=C,1 C=C,§3.1 Structure of Alkenes,3.1.1 乙烯的结构(Ethylene， Ethene),现代物理方法证明,乙烯分子的所有原子在同一平面上， (Planar or flat)其结构如下：,碳原子的SP2杂化,SP2杂化轨道示意图,SP2杂化的特点,SP2 轨道与P轨道的关系,乙烯分子的形成,双键(C=C) =键 + 键 键能 CC 346kJ/mol C=C 610kJ/mol 键键能=610-346=264kJ/mol,Bonding in Ethylene, molecular orbitals,键的特点, 不如键牢固（Sideways overlap）。 不能自由旋转。 电子云沿键轴上下分布，不集中，易极化， 发生反应。 不能独立存在。,The bond must break for rotation to take place around a carbon-carbon double bond, bond (p orbitals are parallel),Broken bond after rotation (p orbitals are perpendicular),3.1.2 烯烃的结构特征,1 双键碳是sp2杂化。 2 键是由p轨道侧面重叠形成。 3 由于室温下双键不能自由旋转， 所以烯烃有几何（Z,E）异构体。,cis- and trans- isomers are different compounds with different physical properties!,3-D Molecules:,Cis and trans isomers can be interconverted,3.1.3 Cis-Trans Isomerism in Alkenes,cis-2-Butene,trans-2-Butene,The cis isomer has the two methyl groups on the same side of the double bond, and the trans isomer has the methyl group on opposite sides.,The requirement for cis-trans isomerism in alkenes,These two compounds are identical; they are not cis-trans isomers.,These two compounds are not identical; they are cis-trans isomers.,Conclusion: Compounds that have one of their carbons bonded to identical groups cant exist as cis-trans isomers. Only when both carbons are bonded to two different groups are cis-trans isomers possible.,3.2.1 烯烃的同分异构现象,烯烃的同分异构现象比烷烃的要复杂，除碳干异构外，还有由于双键的位置不同引起的位置异构和双键两侧的基团在空间的位置不同引起的顺反异构。,§3.2 烯烃的异构和命名,1)构造异构 （Constitution isomerism）,碳干异构,1-Butene 2-Butene 2-Methylpropene,位置异构,2) 顺反异构 (Cis-Trans Isomerism),产生顺反异构体的条件： 构成双键的任何一个碳原子上所连的两个基团要不相同。 必要条件：双键 充分条件：连接基团不同,顺反异构体的物理性质不同，因而分离它们并不很难。,1. Common name,3.2.2 烯烃的命名 (Naming Alkenes),Ethene,2-Methylpropene,2-Methyl-1,3-butadiene,These common names often used and are recognized by IUPAC.,2 . Systematic Nomenclature of Alkenes,1）选择含碳碳双键的最长碳链为主链，为某烯。 2）从最靠近双键的一端开始，将主链碳原子依次编号。 3）将双键的位置标明在烯烃名称的前面 （只写出双键碳原子中位次较小的一个）。 4）其它同烷烃的命名原则。,2,5-二甲基-2-己烯 (2,5-dimethyl-2-hexene),顺反异构体的命名,1）顺反命名法： 即在系统名称前加一“顺”或“反”字。,The cis-trans naming system only works with disubstituted alkenes-compounds that have two substituents other than hydrogen on the double bond.,Trans-,Cis-,Cis-trans naming system,With trisubstituted and tetrasubstituted double bonds, the cis-trans naming system does not work , a more general method is needed for describing double-bond geometry.,Trisubstituted or tetrasubstituted alkenes-compounds that have three or four substituents other than hydrogen on the double bond.,2) E,Z Designation and Sequence Rules,According to the E,Z system of nomenclature, a set of sequence rules is used to assign priorities to the substituent groups on the double bond carbons. When each double bonded carbon atom is considered separately, the sequence rules are used to decide which of the groups attached to each is higher in priority. If the higher-priority groups on each carbon are on the same side of the double bond, the alkene is designated Z. If the higher-priority groups are on opposite sides, the alkene is designated E.,Z, for German zusammen, meaning “together” E, for German entgegen, meaning “opposite”,分别按“次序规则”比较两个双键碳原子上的取代基团，定出较优基团，如果两个双键碳上的较优基团位于双键的同侧，则为Z构型，反之为E构型。,Z是德文 Zusammen 的字头，同一侧的意思。 E是德文 Entgegen 的字头，是相反的意思。,2) Z、E命名法,(E)-2-Bromo-1-chloropropene,2) E, Z Designation and Sequence Rules,E double bond (Higher priority groups are on opposite sides),Z double bond (Higher priority groups are on same side),Sequence Rules:,Considering the double-bond carbons separately, look at the two atoms directly attached to each and rank them according to atomic number.,(Z)-2-Chloro- 2- butene,(E)-2-Chloro- 2- butene,(Cis)-,(Trans)-,2. If a decision cant be reached by ranking the first atoms in the substituent, look at the second, third, or fourth atoms away from the double-bond carbons until the first different is found.,Sequence Rules:,Lower Higher,Lower Higher,3. Multiple-bonded atoms are equivalent to the same number of single-bonded atoms.,(Z)-3-甲基-4-异丙基-3-庚烯,(E)-3-Methyl-1,3-pentadiene,E configuration,Z configuration,CH3CH=CH 1-丙烯基 1-propenyl,CH2=CHCH2 2-丙烯基或烯丙基 allyl,CH2=C 1甲基乙烯基或异丙烯基 isopropenyl,CH2=CH 乙烯基 Vinyl,烯基 烯烃分子去掉一个氢原子后剩下的一价基团。,3) 几个重要的烯基(alkenyl),二 亚基,H2C= CH3CH= (CH3)2C= 亚甲基 亚乙基 亚异丙基 Methylidene ethylidene isopropylidene CH2 CH2CH2 CH2CH2CH2 亚甲基 1,2- 亚乙基 1,3- 亚丙基 Methylene ethylene (dimethylene) trimethylene,两种亚基：中文名称通过前面的编号来区别， 英文名称通过词尾来区别,有两个自由价的基称为亚基。,随分子量的增加而升高；,碳原子数相同，直链烯烃的比带支链的高；, 物质状态,烯烃在室温常压下：1C4C (g)，5C16C (l)，17C(s), Boiling point 沸点 bp.,-6.3,-6.9,bp./,§ 3.3 The Physical Properties of Alkenes 烯烃的物理性质,碳链相同，双键向中间移动沸点升高；,双键位置相同，顺式的烯烃沸点高。,-6.3,3.7,bp./,0.88,原因：顺-2-丁烯偶极矩为0.33D，反-2-丁烯偶极矩为0。,-138.9,-105.6,mp./, melting point 熔点 mp.,也随分子量的增加而升高；,碳链相同，双键向中间移动熔点也升高；,同分异构体中，对称性大的烯烃熔点高。, Solubility 溶解度,烯烃的相对密度都小于1，但比相应的烷烃大。, Density 相对密度,在水里的溶解度很小，但也比烷烃大；,在亚铜盐或银盐的水溶液中，溶解度很大。,非常活泼C=C,C=C 加成 饱和烃,氧化-发生在富裕电子部位,-H: 烯丙位氢活波,可被卤代.,§3.4 烯烃的化学性质 p48,§3.3 烯烃的物理性质（略） p47,3.4 The Chemical Properties of Alkenes 烯烃的化学性质,-C 是与官能团相连的碳。,-H,-C上的氢，-H 较其他氢活泼。,非常活泼C=C,Structure of Alkene,一、烯烃的亲电加成反应,Electrophilic addition,在烯烃分子中，由于电子具流动性，易被极化，因而烯烃具有供电子性能，易受到缺电子试剂（亲电试剂）的进攻而发生反应，这种由亲电试剂的作用而引起的加成反应称为亲电加成反应。,Alkenes behave as nucleophiles (Lewis bases) in polar reactions. The carbon-carbon double bond is electron-rich and can donate a pair of electrons to an electrophile (Lewis acids).,试剂 reagent,亲电试剂 （亲电体） Electrophilic reagent (electrophiles),亲核试剂 （亲核体） Nucleophilic reagent (nucleophiles),These are electrophiles because they can accept a pair of electrons,These are nucleophiles because they have a pair of electrons to share!,亲电试剂,亲核试剂,1. Electrophilic Addition of HX to Alkenes,1) The order of reactivity of hydrogen halides to alkenes: HI HBr HCl HF (HF的加成无实用价值):,The reaction occurs in two steps and involves electrophile- nucleophile interaction.,2) Mechanism:,The electrophilic addition reaction of ethylene and HBr.,决速步骤,Reaction progress,Energy,Ea1,Transition state,TS-1,Ea2,TS-2,Carbocation intermediate,Reaction energy diagram for the two step electrophilic Addition of HBr to alkene. The first step is slower than The second step.,3) Markovnikovs Rule:,Two possible products,Not formed,Sole product,unsymmetrical alkenes,Regioselective reaction is a reaction in which two isomeric products could be obtained, but one predominates.,Markovnikovs rule:,In the addition of HX to unsymmetrical alkenes, the H attaches to the carbon with fewer alkyl substituents and the X attaches to the carbon with more substituents.,The reason for Markovnikovs rule:,More stable,less stable,Progress of carbocation formation,Energy diagram for the protonation of 2-methypropene,E,E(1o),E(3o),Transition state,Reaction takes this course,Summary:,Electrophilic addition to an unsymmetrically substituted alkene gives the more highly substituted carbocation. 2. A more highly substituted carbocation is more stable than a less highly substituted one.,Carbocation structure and stability,P 52,One way of determing carbocation stabilities is to measure the amount of energy required to form the cabocation by dissociation of the corresponding alkyl halid.,Dissociation enthalpy(焓):,Higher Lower,Tertiary (3o) Secondary (2o) Primary (1o) Methyl R3C+ R2CH+ RCH2+ CH3+,The stability order of carbocations:,The reasons for Carbocations stability,Inductive effects (p67) （诱导效应）,3 methyl groups Donating electrons,2,1,0,电负性：C sp2 C sp3,2) Hyperconjugation （超共轭效应）,9 -p,6 -p,3 -p,0 -p,Delocalization of Electrons 电子的超共轭效应,CH3CH2+ ethyl cation,Delocalization of electrons by the overlap of a bond orbital with an empty p orbital is called hyperconjugation(超共轭).,-p 超共轭,The Restatement for Markovnikovs Rule:,Electrophilic addtions of HX to alkenes take place through Carbocation intermediates formed by reaction of the Nucleophilic alkene bond with electrophilic H+.,In the addition of HX to an unsymmetrically substituted alkenes, the more stable carbocation intermediate is formed.,Markovnikovs rule 推广:,( X2 + H2O) different mechanism,Vladimir Vasilevich Markovnikov (18371904),Evidence for the Mechanism of electrophilic addition: Carbocation Rearrangement,Carbocation Rearrangement,碳正离子三个特性：,取代 (Substitution) 重排 (Rearrangement) 消除 (Elimination),Feature of Carbocation Chemistry,Problem:,On treatment with HBr, vinylcyclohexane undergoes addition and rearrangement to yield 1-bromo-1-ethylcyclohexane. Using curved arrows, propose a mechanism to account for this result.,2. Addition of H2SO4 and H2O to Alkenes,P 57,Sulfuric acid,烯烃的间接水合：Hydration,应用：1）烯烃的间接水合： 用于2°醇的制备 2）分离除去烷烃、卤代烃中少量的烯烃,不对称烯烃的间接水合：符合马氏规则,Hydration,Acid-Catalyzed Hydration of Alkenes,烯烃的直接水合：制备醇（需要强酸做催化剂）,In a dilute acid medium, Markovnikovs rule is followed,mechanism for the acid-catalyzed addition of water,（1）反应机理与烯烃加HX一致。 （如加中性分子多一步失H+）,CH2=C(CH3)2 + H+ CH3C+(CH3)2 CH3C(CH3)2 CH3C(CH3)2,慢,H2O,OH2,+,OH,-H+,（2）反应符合马氏规则。 （3）反应条件：与水、弱有机酸、醇、酚的反应 要用强酸作催化剂。,烯烃与水、硫酸、有机酸、醇、酚的反应,3. Addition of Halogens to Alkenes,Bromine and chlorine add readily to alkene to yield 1,2-dihalides.,Approximately 6 million tons per year of 1,2-dichloroethane are synthesized by the addition of Cl2 to ethylene. The product is used both as a solvent and as starting material for use in the manufacture of Poly(vinyl chlorine), PVC.,Addition of Halogens to Alkenes,Disappearance of the reddish- brown color of Br2,Addition of Halogens to Alkenes,Fluorine is too reactive and difficult to control for most laboratory application, and Iodine does not react with most alkenes.,卤素的反应活性次序： F2 Cl2 Br2 I2 。 氟与烯烃的反应太剧烈，往往使碳链断裂；碘与烯烃难于起反应。故烯烃的加卤素实际上是指加氯或加溴。烯烃也能与卤水等（混合物）起加成反应，有的在有机合成上很有用。,Mechanism for addition of bromine to alkenes,Two steps: Formation of a bromonium ion intermdiate 2) Anti-attack,(Bridged intermediate),Formation of brommonium ion,The brommonium bridged ion is positively charged and of high energy .,Evidence for anti- addition,Solo product,Strong evidence for existence of brommonium ion,More recently, strong evidence for supporting the mechanism of brommonium ion has come from the work of George Olah, who has prepared and studied stale solution of cyclic bromonium ions in liquid SO2. Theres no question that bromonium ions exist.,Addition of Halogens and water to Alkenes,1) 符合马氏规则 2) 反式加成 3) 产物：Halohydrin,烯烃和次卤酸的反式亲电加成,Evidence for anti-Addition,Mechanism for Halohydrin Formation,Regioselectivity,more stable transition state,less stable transition state,What will thess reactions give?,Mixed Addition,Question: Would you expect to find 1,2-dichloroethane as a product in this reaction? Explain.,4.1. 硼氢化反应（Hydroboration ）,4. Addition of Borane to Alkenes,乙硼烷是甲硼烷的二聚体，反应时乙硼烷离解成甲硼烷 .,4.1. 硼氢化反应（Hydroboration ）,三中心二电子,Borane is highly reactive because the boran atom has only six electrons in its valence shell. In tetrahydrofuran(THF) solution,硼氢化反应（Hydroboration ）,乙硼烷中成键原子的电负性：B2.0; H2.1）,-,+,不对称烯烃的硼氢化反应（Hydroboration ）,电负性：B2.0; H2.1）,Step1:,Step2:,Step3:,-,+,Mechanism of the Hydroboration,The reaction occurs in a single step, in which both C-H and C-B bonds form at the same time and on the same face of the double bond.,硼氢化反应的特点 *1 立体化学：顺型加成（烯烃构型不会改变） *2 区域选择性反马氏规则。 *3 因为是一步反应，反应只经过一个环状过渡态, 所以不会有重排产物产生。,Anti-Markovnikov addition,Markovnikov addition,此反应是用末端烯烃来制取伯醇的好方法，其操作简单，副反应少，产率高。在有机合成上具有重要的应用价值。 硼氢化反应是美国化学家布朗(Brown)于1957年发现的，由此布朗获得了1979年的诺贝尔化学奖。,硼氢化氧化反应 (hydroboration/oxidation),简写为：,反应的总结果：烯烃与水的加成，反马氏规则。,P 296,硼氢化氧化反应: 烯烃与水的加成，反马氏规则。,The mechanism of the oxidation reaction,Stereochemistry of Hydroboration： Syn-addition,Main product,trans-2-Methylcyclopentane (85%),Stereochemistry of Hydroboration： cis-addition,Retention of configuration in oxidation of a borane,The oxidation and hydrolysis of boranes,Syn-addition,Syn addition versus anti addition,syn addition : two atoms or groups add to the same face of a double bond. anti addition: two atoms or groups add to opposite faces of the double bond, the process is called,硼氢化-氧化反应的应用,*1 CH3CH=CH2,B2H6,H2O2， HO-,H2O,CH3CH2CH2OH,*2,B2H6,H2O2， HO-,H2O,反应的总结果：烯烃与水的加成，反马氏规则,*1 CH3CH=CH2,B2H6,H2O2， HO-,H2O,CH3CH2CH2OH,*2,B2H6,H2O2， HO-,H2O,*3,B2H6,H2O2， HO-,H2O,*3,后面讲,硼氢化氧化反应 (hydroboration/oxidation),Summary of Alcohol Synthesis from Alkenes,P 296,5. 羟汞化脱汞反应 Addition of Water to Alkenes: Oxymercuration,反应的总结果：烯烃与水的加成，符合马氏规则。,反应的特点： *1 高区域选择性符合马氏规则（high regioselectivity） *2 反应速率快，条件温和，是实验室制备醇的一种方法 。 *3 没有重排产物产生。,Mechanism of Oxymercuration,6. 与烯烃的加成 (查资料完成),加成反应机理：生成碳正离子中间体 (Carbocation),-消除,Why?,二、烯烃的自由基加成反应 Radical Addition,P57.,过氧化物效应(卡拉施Kharasch效应)： 当有过氧化物（Peroxide如 H2O2, R-O-O-R等）存在时，不对称烯烃与HBr的加成产物不符合马氏规则（反马氏取向）的现象称为过氧化物效应。 自由基加成反应： 烯烃受自由基进攻而发生的加成反应。,反马氏规则产物,自由基加成反应机理：,链增长 CH3CH=CH2 + Br CH3CHCH2Br CH3CHCH2Br + HBr CH3CH2CH2Br + Br ,链终止： （略）,CH3CHBrCH2,more stable (formed),less stable (not formed),自由基加成的适用范围: HBr HCl，HI不能发生自由基加成反应.,Anti-Markovnikov additon of HBr,This effect is not observed with HCl or HI . Hydrogen chloride does not undergo free-radical addition to alkenes. Because of the relative slowness of the homolytic cleavage of HCl into radicals. Hydrogen iodide does not undergo this reaction because the additon of I. to alkenes is endothermotic （吸热的） and too slow to sustain a chain reaction.,烷基自由基的相对稳定性,复习回忆：,如何解释此稳定性次序？,The reasons for alkyl radicals stability,Inductive effects （诱导效应）,3 methyl groups Donating electrons,2,1,0,电负性：C sp2 C sp3,2) Hyperconjugation （超共轭效应）,Delocalization of Electrons 电子的超共轭效应,CH3CH2. ethyl radical,Delocalization of electrons by the overlap of a bond orbital with an empty p orbital is called hyperconjugation(超共轭).,-p 超共轭,三、烯烃的还原 （Reduction of Alkenes）,1. Catalytic Hydrogenation,p60,In the presence of a metal catalyst such as platinum, palladium, or nickel, hydrogen adds to the double bond of an alkene to for