附件2 粒大浮 教 案 2003~~2004学年第Ⅰ学期 院(系、所、部)化学与环境学院有机化学研究所 教研室有机化学 课程名称有机化学(双语教学 授课对象化学教育 授课教师杨定乔 职称职务教授 教材名称 Organic Chemistry 2003年09月01日
附件 2 教 案 2003~~ 2004 学年 第 I 学期 院（系、所、部）化学与环境学院有机化学研究所 教 研 室 有机化学 课 程 名 称 有机化学(双语教学) 授 课 对 象 化学教育 授 课 教 师 杨定乔 职 称 职 务 教授 教 材 名 称 Organic Chemistry 2003 年 09 月 01 日
有机化学(双语教学)课程教案 授课题目(教学章节或主题):第四章炔烃与二烯|授课类型|理论课 烃( Alkynes and Dienes) 第4周第13-16 授课时间 教学目标或要求:了解炔烃的结构理论以及炔烃的化学性质。掌握共轭效应和亲电加 成理论 教学内容(包括基本内容、重点、难点) Reactions of alkynes Addition of Halogen Acids to Alkenes The addition of halogen acids to alkynes is a stepwise process which involves a solvent-equilibrated carbocation intermediate. The formation of this intermediate is initiated through a simple acid-base equilibrium in which the halogen acid donates a proton to the alkyne T-system, which is functioning as a Lewis base. The protonated T-system has a short lifetime and can rapidly revert to starting materials, or can rearrange from a(cationic) protonated T-bond, to an sp= sigma bond adjacent to an sp carbocation center. If the alkyne is unsymmetrical, the protonated T-cloud intermediate can break down by two pathways to potentially form carbocations having differing ground-state energies. The reaction pathways leading from this intermediate to the two carbocations will differ in energy, and, in general, the pathway leading to the more stable intermediate will be of lower energy and will be the preferred is best able to stabilize the cationic center. In simple unstrained e which pathway. The resulting carbocation is formed on the carbon of the alkyne which non-conjugated systems, without adjacent heteroatoms, the order of stability of carbocations formed from alkyne protonation will be secondary primary Since secondary centers have no attached and primary centers have one, there is an apparent inverse relationship between the number of attached hydrogens and the likelihood that the carbocation will form at that center and this is
有机化学（双语教学） 课程教案 授课题目（教学章节或主题）：第四章．炔烃与二烯 烃（Alkynes and Dienes） 授课类型 理论课 授课时间 第 4 周第 13-16 节 教学目标或要求：了解炔烃的结构理论以及炔烃的化学性质。掌握共轭效应和亲电加 成理论。 教学内容（包括基本内容、重点、难点）： Reactions of Alkynes Addition of Halogen Acids to Alkenes The addition of halogen acids to alkynes is a stepwise process which generally involves a solvent-equilibrated carbocation intermediate. The formation of this intermediate is initiated through a simple acid-base equilibrium in which the halogen acid donates a proton to the alkyne -system, which is functioning as a Lewis base. The protonated -system has a short lifetime and can rapidly revert to starting materials, or can rearrange from a (cationic) protonated -bond, to an sp2 sigma bond adjacent to an sp2 carbocation center. If the alkyne is unsymmetrical, the protonated -cloud intermediate can break down by two pathways to potentially form carbocations having differing ground-state energies. The reaction pathways leading from this intermediate to the two carbocations will differ in energy, and, in general, the pathway leading to the more stable intermediate will be of lower energy, and will be the preferred pathway. The resulting carbocation is formed on the carbon of the alkyne which is best able to stabilize the cationic center. In simple unstrained non-conjugated systems, without adjacent heteroatoms, the order of stability of carbocations formed from alkyne protonation will be secondary > primary. Since secondary centers have no attached and primary centers have one, there is an apparent inverse relationship between the "number of attached hydrogens" and the likelihood that the carbocation will form at that center and this is
another example of Markovnikoy's Rule, which was described for alkenes Once the carbocation is formed. the most favorable reaction will involve the addition of a nucleophile to form a viny l halide intermediate. This alkene can now undergo a second protonation step, just like any other alkene, except that the carbocation will always be formed on the carbon bearing the halogen, since this carbocation is now stabilized by resonance with the halonium ion. The final result of the addition is that two moles of halogen halide are added, to give a 1.1-dihalide HC≡ 2 HCI H-CH2 stepwise addition of Ao mer ofHX Markovnikov region hemistry Addition of Halogen to Alkynes The addition of halogen to alkynes is a stepwise process involving a"halonium ion intermediate. The formation of this intermediate is initiated through attack of halogen on the alkyne T-system, to form the cyclic halonium ion(i.e bromonium or chloronium ion) and expel the halogen anion (i.e, bromide or chloride). This intermediate is highly electrophilic and reacts rapidly with the best nucleophile in the system; that is, the halide anion expelled in the previous step. Attack by halide generates a viny l halide, which is an alkene and can undergo a second addition of halogen. The final product of the reaction is therefore a 1,1.2.2-tetrahalide had HgC H3 stepwise addition of nso maer of x2
another example of Markovnikov's Rule, which was described for alkenes. Once the carbocation is formed, the most favorable reaction will involve the addition of a nucleophile to form a vinyl halide intermediate. This alkene can now undergo a second protonation step, just like any other alkene, except that the carbocation will always be formed on the carbon bearing the halogen, since this carbocation is now stabilized by resonance with the halonium ion. The final result of the addition is that two moles of halogen halide are added, to give a 1,1-dihalide. Addition of Halogen to Alkynes The addition of halogen to alkynes is a stepwise process involving a "halonium" ion intermediate. The formation of this intermediate is initiated through attack of halogen on the alkyne -system, to form the cyclic halonium ion (i.e., bromonium or chloronium ion) and expel the halogen anion (i.e., bromide or chloride). This intermediate is highly electrophilic and reacts rapidly with the best nucleophile in the system; that is, the halide anion expelled in the previous step. Attack by halide generates a vinyl halide, which is an alkene and can undergo a second addition of halogen. The final product of the reaction is therefore a 1,1,2,2-tetrahalide
Addition of Water to Alkynes The mercury-catalyzed addition of water to alkynes is another example of a stepwise process which generally involves a solvent-equilibrated carbocation intermediate. The formation of this intermediate is initiated through a simple acid-base equilibrium in which the mercury ion interacts with the alkyne T-system, which is functioning as a Lewis base. The chelated I>-system rearranges to form an sp? sigma bond adjacent to an sp? carbocation center If the alkyne is unsymmetrical, two carbocations are possible and the addition will proceed to form the most stable carbocation. As before, secondary centers will be favored over primary, and overall addition of water will follow the order predicted by Markovnikov's Rule. Addition of water forms a viny I alcohol, which is termed an" enol". Enols are unstable compounds which rapidly interconvert with the corresponding carbonyl compound. Hence, the final product of the hydration reaction is the formation of an aldehyde or ketone, with the oxygen bonded to the carbon of the alkyne which would ultimately yield the most stable carbocation H H3O'IHg Markoymilkow an ena intermediate regiochemistry R-C=C-H- HH2o,y Hg SO4 w Hydroboration of Alkynes The reaction of BH, with an alkyne begins with the Lewis acid chelation of the alkyne T-system by the boron This complex then rearranges in a more-or-less concerted manner to produce the viny l borane The reaction seems to be dominated
Addition of Water to Alkynes The mercury-catalyzed addition of water to alkynes is another example of a stepwise process which generally involves a solvent-equilibrated carbocation intermediate. The formation of this intermediate is initiated through a simple acid-base equilibrium in which the mercury ion interacts with the alkyne -system, which is functioning as a Lewis base. The chelated >-system rearranges to form an sp2 sigma bond adjacent to an sp2 carbocation center. If the alkyne is unsymmetrical, two carbocations are possible and the addition will proceed to form the most stable carbocation. As before, secondary centers will be favored over primary, and overall addition of water will follow the order predicted by Markovnikov's Rule. Addition of water forms a vinyl alcohol, which is termed an "enol". Enols are unstable compounds which rapidly interconvert with the corresponding carbonyl compound. Hence, the final product of the hydration reaction is the formation of an aldehyde or ketone, with the oxygen bonded to the carbon of the alkyne which would ultimately yield the most stable carbocation. Hydroboration of Alkynes The reaction of BH3 with an alkyne begins with the Lewis acid chelation of the alkyne -system by the boron. This complex then rearranges in a more-or-less concerted manner to produce the vinyl borane. The reaction seems to be dominated
by steric effects and the boron attaches to the least hindered carbon. All three equivalents of the boron hydride can be utilized in separate reactions to give a triviny l borane. The organoborane which is formed can be oxidized by alkaline peroxide to form the alcohol by a mechanism which involves attack of peroxide anion on the boron, followed by alkyl migration to the oxygen, with loss of hydroxide anion. The resulting borate ester is rapidly hydrolyzed by the alkaline conditions to form an"". Rearrangement of the enol to the corresponding carbony l compound yields an aldehyde or ketone, with the oxygen bonded to the carbon of the alkyne which would generally yield the least stable carbocation (generally, antiMarkovnikov addition) H 2. H202, HoH- ape varkormikon regiochemistry Reduction of Alkynes Catalytic hydrogenation of alkynes with H, and a standard catalyst (Pt or Pd supported on charcoal, etc.) produces the corresponding alkane. However partial reduction of an alkyne to an alkene is possible using a poisoned catalyst", such as Pd or Pt on BaSO, or with the "Lindar Catalyst. In these reactions, addition of hydrogen is syn(cis) to yield the cis alkene. The transfer of hydrogen occurs in a strictly cis manner, probably due to the geometric constraints of the metal surface. The detailed mechanism is not trivial, and probably involves several metal-carbon bonded species. CH2cH3 H2, Pdrc CHCH3 HC=C-CH H,C-CHa-Ch ①- H,LIndar catalyst (also R or Pt/Basos Alkynes can also be partially reduced to trans-alkenes using a dissolving metal
by steric effects and the boron attaches to the least hindered carbon. All three equivalents of the boron hydride can be utilized in separate reactions to give a trivinyl borane. The organoborane which is formed can be oxidized by alkaline peroxide to form the alcohol by a mechanism which involves attack of peroxide anion on the boron, followed by alkyl migration to the oxygen, with loss of hydroxide anion. The resulting borate ester is rapidly hydrolyzed by the alkaline conditions to form an "enol". Rearrangement of the enol to the corresponding carbonyl compound yields an aldehyde or ketone, with the oxygen bonded to the carbon of the alkyne which would generally yield the least stable carbocation (generally, anti-Markovnikov addition). Reduction of Alkynes Catalytic hydrogenation of alkynes with H2 and a standard catalyst (Pt or Pd supported on charcoal, etc.) produces the corresponding alkane. However, partial reduction of an alkyne to an alkene is possible using a "poisoned catalyst", such as Pd or Pt on BaSO4, or with the "Lindar Catalyst". In these reactions, addition of hydrogen is syn (cis) to yield the cis alkene. The transfer of hydrogen occurs in a strictly cis manner, probably due to the geometric constraints of the metal surface. The detailed mechanism is not trivial, and probably involves several metal-carbon bonded species. Alkynes can also be partially reduced to trans-alkenes using a "dissolving metal
reduction, in which the alkyne is formed by a radical mechanism in the presence of Li or Na metal dissolving in liquid ammonia. Please note that this differs from the base sodium amide, which is formed from sodium metal previously dissolved in liquid ammonia fac dissolving metal reduction stepwise addition (radical mec hanism?) to yield &awy or ana product Oxidation of Alkynes Acidic potassium permanganate is a powerful oxidant towards organic molecules and will readily cleave alkynes. Alkyne carbons are converted into carboxylic acids in this reaction H Mno4 H H Alkynes Anions as Nucleophiles Terminal alkynes are slightly acidic and a powerful base such as sodium amide (sodium previously dissolved in liquid ammonia)will react with these compounds to give alkyne anions, which are powerful nucleophiles. The most common reaction in which these nucleophiles are utilized involves reaction with alkyl halides to displace the halogen and form a new alkyne with a longer carbon chain. The mechanism of this reaction an s2 reaction will be discussed in detail in the chapter under alkyl halides
reduction", in which the alkyne is formed by a radical mechanism in the presence of Li or Na metal dissolving in liquid ammonia. Please note that this differs from the base sodium amide, which is formed from sodium metal previously dissolved in liquid ammonia. Oxidation of Alkynes Acidic potassium permanganate is a powerful oxidant towards organic molecules and will readily cleave alkynes. Alkyne carbons are converted into carboxylic acids in this reaction. Alkynes Anions as Nucleophiles Terminal alkynes are slightly acidic and a powerful base such as sodium amide (sodium previously dissolved in liquid ammonia) will react with these compounds to give alkyne anions, which are powerful nucleophiles. The most common reaction in which these nucleophiles are utilized involves reaction with alkyl halides to displace the halogen and form a new alkyne with a longer carbon chain. The mechanism of this reaction, an SN2 reaction, will be discussed in detail in the chapter under alkyl halides
C≡GH+aNH2 C≡C;Na sodium salt of NH3 an $preaction (Substitution, Nucleophilic bimolecular) Con jugated Dienes: Ionic Addition Reactions When compounds containing conjugated double bonds undergo typical ionic alkene addition reactions(addition of HBr or Br, for example), the products which are obtained are not those which would be expected for addition to the individual double bonds in the molecule. For the addition of HBr to 1, 3-butadiene, two products are obtained, 3-bromo-1-butene and 1-bromo-2-butene. These products can be seen to arise from astandard"1. 2-addition to one of the terminal double bond(Markovnikov-style), and from a 1, 4-addition of HBr to the two terminal carbons, with relocation of the double bond onto the central two carbons B +HBr 1 4 addition The formation of these products can be readily understood by examining the mechanism of the addition reaction. Protonation of the con jugated diene on either terminal carbon will generate a carbocation on the adjacent secondary carbon. This carbocation, however, can be stabilized by resonance with the adjacent double bond to give a delocalized carbocation (an allylic carbocation) in which there is positive character on both a secondary center and on the terminal, primary carbon. Since both of these centers share positive character in the resonance hybrid, both are subject to nucleophilic attack by bromide
Conjugated Dienes: Ionic Addition Reactions When compounds containing conjugated double bonds undergo typical ionic alkene addition reactions (addition of HBr or Br2, for example), the products which are obtained are not those which would be expected for addition to the individual double bonds in the molecule. For the addition of HBr to 1,3-butadiene, two products are obtained, 3-bromo-1-butene and 1-bromo-2-butene. These products can be seen to arise from a "standard" 1,2-addition to one of the terminal double bond (Markovnikov-style), and from a 1,4-addition of HBr to the two terminal carbons, with relocation of the double bond onto the central two carbons. The formation of these products can be readily understood by examining the mechanism of the addition reaction. Protonation of the conjugated diene on either terminal carbon will generate a carbocation on the adjacent secondary carbon. This carbocation, however, can be stabilized by resonance with the adjacent double bond to give a delocalized carbocation (an allylic carbocation) in which there is positive character on both a secondary center and on the terminal, primary carbon. Since both of these centers share positive character in the resonance hybrid, both are subject to nucleophilic attack by bromide
anion; at tack on the secondary carbon gives the 1, 2-addition product, and attack on the terminal carbon gives the 1, 4-addition product +HBr allylic carbocation 1 4 addition Protonation on the termimal carbon generates the adstecartantan aith cationic character on both carbons &1 and 3 Some further observations on this reaction reveal the following: The 1, 2-addition product forms rapidly at low temperatures the 1, 4-addition product is predominant at higher temperatures even at low temperatures, 1, 4-addition products will predominate if given enough time the addition of HBr to butadiene is reversible and isolated 1, 2 - addition product will convert to the 1, 4-product at higher temperatures or at longer times These data can be explained using the reaction coordinates shown below. The pathway to form the 1, 2-product must have a lower activation energy, because it forms more rapidly than the 1, 4-product. The 1, 4-product, however, must be more stable than the 1, 2-product because it accumulates at equilibrium (note that the reaction appears freely reversible, since isolated 1, 2-product reverts to 1, 4-, given enough time) The 1 2 addition is faster, but forms a less stable product, while 1 4 addition is slower, but gives a more stable product. At equilibrum (Thermodynamic Control) the more stable 1 4 addition product will be favored, but if you examine the initial product distnibution, the more rapidly formed 1 2 product will predomina te Kime smaller△G°,les3 favored at equilibrium but formed faster larger△G°,more favored at equilibrium
anion; attack on the secondary carbon gives the 1,2-addition product, and attack on the terminal carbon gives the 1,4-addition product. Some further observations on this reaction reveal the following: • The 1,2- addition product forms rapidly at low temperatures; • the 1,4-addition product is predominant at higher temperatures; • even at low temperatures, 1,4-addition products will predominate if given enough time; • the addition of HBr to butadiene is reversible and isolated 1,2-addition product will convert to the 1,4-product at higher temperatures or at longer times. These data can be explained using the reaction coordinates shown below. The pathway to form the 1,2-product must have a lower activation energy, because it forms more rapidly than the 1,4-product. The 1,4-product, however, must be more stable than the 1,2-product because it accumulates at equilibrium (note that the reaction appears freely reversible, since isolated 1,2-product reverts to 1,4-, given enough time)
The 1, 2-addition product is referred to as the kinetic product since it is formed faster. The 1, 4-product is the thermodynamic product since it is thermodynamically more stable. A similar product distribution observed for Br, addition through a similar mechanis Con jugated Dienes: Cycloaddition Reactions Conjugated dienes react with alkenes to yield cyclohexene derivatives. The reaction is termed a 4+2 cycloaddition and is generally referred to as the Diels-Alder reaction. The reactants in the cycloaddition are referred to generically, as a diene and a dienophile. The reaction usually requires heat and pressure to give good yields and is promoted by electron withdrawing groups on the dienophile and electron donating groups on the diene The mechanism of the reaction is generally described as concerted involving an electrocyclic transition state in which the two new sigma bonds form simultaneously; this is usually represented by showing the electron movement with curved arrows, as shown above. Since both bonds form at the same time it is necessary for the diene to be in the proper conformation prior to the reaction, that is, the s-cis conformation is required, and dienes which adopt this conformation will not react free otation s-trans S- C s-cis stereochemistry is required for a 4+2 cycloaddition reaction Examination of the animation shown above for the reaction of ethene with butadiene clearly shows that the initial product of the reaction is the boat cyclohexene. This can also be appreciated by examination of the sequence of images shown below for the reaction of butadiene with butenedinitrile. lining up the reacting centers and allowing the cycloaddition to proceed generates the structure shown on the right. Rotating this along the X-axis(with the double bond remaining in the back) shows the compound in the boat" conformation
The 1,2-addition product is referred to as the kinetic product since it is formed faster. The 1,4-product is the thermodynamic product since it is thermodynamically more stable. A similar product distribution is observed for Br2 addition, through a similar mechanis Conjugated Dienes: Cycloaddition Reactions Conjugated dienes react with alkenes to yield cyclohexene derivatives. The reaction is termed a 4+2 cycloaddition and is generally referred to as the Diels-Alder Reaction. The reactants in the cycloaddition are referred to, generically, as a diene and a dienophile. The reaction usually requires heat and pressure to give good yields and is promoted by electron withdrawing groups on the dienophile and electron donating groups on the diene. The mechanism of the reaction is generally described as concerted involving an electrocyclic transition state in which the two new sigma bonds form simultaneously; this is usually represented by showing the electron movement with "curved arrows", as shown above. Since both bonds form at the same time, it is necessary for the diene to be in the proper conformation prior to the reaction, that is, the s-cis conformation is required, and dienes which cannot adopt this conformation will not react. Examination of the animation shown above for the reaction of ethene with butadiene clearly shows that the initial product of the reaction is the boat cyclohexene. This can also be appreciated by examination of the sequence of images shown below for the reaction of butadiene with butenedinitrile. Lining up the reacting centers and allowing the cycloaddition to proceed generates the structure shown on the right. Rotating this along the X-axis (with the double bond remaining in the back) shows the compound in the "boat" conformation
Converting this to a chair by rotating one end down (and rotating the molecule slightly along the Z-axis) gives the middle image on the second row, which is an idealized cyclohexene chair. In fact, the geometry of the double bond contorts the molecule as shown on the right, but the idealized chair is useful to establish stereochemical relationship between substituents on the diene and dienophile, as they appear in the cyclohexene product. .rotate along the x axis to give the intermediate boat Following a similar sequence of steps to those shown above, the product of the reaction of trans-trans-2, 3-hexadiene with trans-2-butene can be shown to be the tetramethyl cyclohexene shown below. Using the numbering scheme shown(the corresponding numbers are also shown on the reactants), the methyl groups of other(2, 3- in the molecule)and they are trans-(both are equatorial),ag the diene are 1, 4-relative to each other and they are cis-(one is axial, on is equatorial). The methyl groups of the dienophile are 1, 2-relative to ea N 14-methyls oNpY-die H. (NYRY-YRydiene 4uay-23-methyls a general rule can be established, as shown below, that the stereochemistry
Converting this to a "chair" by rotating one end down (and rotating the molecule slightly along the Z-axis) gives the middle image on the second row, which is an idealized cyclohexene "chair". In fact, the geometry of the double bond contorts the molecule as shown on the right, but the idealized chair is useful to establish stereochemical relationship between substituents on the diene and dienophile, as they appear in the cyclohexene product. ...rotate along the x-axis to give the intermediate "boat"... Following a similar sequence of steps to those shown above, the product of the reaction of trans-trans-2,3-hexadiene with trans-2-butene can be shown to be the tetramethyl cyclohexene shown below. Using the numbering scheme shown (the corresponding numbers are also shown on the reactants), the methyl groups of the diene are 1,4-relative to each other and they are cis- (one is axial, one is equatorial). The methyl groups of the dienophile are 1,2-relative to each other (2,3- in the molecule) and they are trans- (both are equatorial). A general rule can be established, as shown below, that the stereochemistry