第七章碳正离子1

1 第七章第七章 碳正离子碳正离子((CarbocationsCarbocations)) 碳正离子的生成碳正离子的生成 碳正离子的结构碳正离子的结构 碳正离子的稳定性碳正离子的稳定性 碳正离子的反应碳正离子的反应 非经典碳正离子非经典碳正离子 引言引言 (H3C)3C F + SbF3 (CH3)3C+SbF6- 19621962年年,Olah,Olah发现发现:: 用用NMRNMR和和CNMRCNMR检测到检测到.. C CH3 H3C H CH3 AlCl3 + HAlCl3-C CH3 H3C CH3 X=H: X=F, Cl, Br, I: C CH3 H3C CH3 Cl AlCl3 + AlCl4-C CH3 H3C CH3 1)1)反应物直接解离反应物直接解离:: RX R X 11正碳离子的生成：正碳离子的生成： Ph CH Cl Ph Ph2CH Cl C CH3 H3C CH3 OTs + OTs-C CH3 H3C CH3 X=OTs酯类衍生物: CH3COF BF3 CH3CO BF4 C R R R OCOCl + Cl- + CO2C R R R X=OCOZ,其中Z=Cl, Br, I 推动力为失去二氧化碳 C R R R OSOCl + Cl- + SO2C R R R 氯亚磺酸酯也属于此类: R O R' H + R O R' + R+ + R'OHH H2OR OH H ROH2 R X=H2O or ROH Create PDF with GO2PDF for free, if you wish to remove this line, click here to buy Virtual PDF Printer 2 COOH H+ COOH2 + CO+ + H2O CO + + X=CO X=CO2 RCOOAgBr2 R + + Br- + AgBr + CO2 2)2)质子或其它阳离子对不饱和键的加成质子或其它阳离子对不饱和键的加成 C Z H C ZH Z: O,C,S,N H+ + H Cl H+ + 形成非经典碳正离子形成非经典碳正离子:: 3)由其它正离子转化而生成 N2 NH2 N2NaNO3 HCl H H Ph3CSbF6 SbF6 - 2 .正碳离子的稳定性： CH3 3C CH3 2CH CH3CH2 CH3> > > σ- p超共轭效应： A 1）电子效应的影响 B 烯丙型正碳离子： CH2 CH CH2 CH2 CH CH2 p-π共轭 电子离域 正电荷分散程度大 共轭体系的数目越多，正碳离子越稳定： >>3CCH2 CH 2CHCH2 CH CH2CH2 CH > O2N CH2CH3 CH2 CH2 > Ph3C > Ph2CH > PhCH2 + ++ (CF3)3C+ 极不稳定 Create PDF with GO2PDF for free, if you wish to remove this line, click here to buy Virtual PDF Printer 3 C 乙烯型正碳离子： C原子进行sp2杂化， p轨道 用于形成π键，空着的是sp2 杂化轨道，使正电荷集中。 苯基正离子： 结构同乙烯型正碳离子，正电荷 集中在sp2杂化轨道上。 此二类正碳离子稳定性极差。 22））..芳构化效应芳构化效应 稳定性比 高 倍(C6H5)3C+ 1011 (C6H5)3C+ + H H (C6H5)3CH + + + 33））空间效应空间效应 张力增加，不稳定 ++ CN > CH3 Cl CH3 + Cl-+ 4）溶剂效应： 1) 极性溶剂的诱导极化作用， 利于底物的解离。 2)极性溶剂使正碳离子稳定： 4 碳正离子的反应 与亲核试剂作用---具有电子对的物质结合 （Lewis酸碱反应） 脱去氢离子生成烯烃 重排为更稳定的碳正离子 加成反应 Create PDF with GO2PDF for free, if you wish to remove this line, click here to buy Virtual PDF Printer 4 1 与亲核试剂作用 R+ + Y- R-Y 可能是OH-、卤离子或任何其它阴离子；也可能 是带有电子对的中性物种，在后一种情况下，产物是带电荷的。 SN 反应 一 SN1 反应 C Cl -L - C+ C NuNu - CNu+ 1 烃基结构的影响 2 离去基团的影响 4 亲核试剂的影响 3 溶剂的影响 ※ C6H5CHCH3 OCH3 R C6H5CH(Br)CH3 CH3OH 27%构型翻转，73%外消旋化 （二） SN反应的立体化学及邻基参与问题 C H3C H C Br O OH NaOH H2O C H3C H C HO O O- （构型保持） 构型保持的取代 I OH HCl I Cl C C Br H H OH CH3 H3C HBr + C C Br H H Br CH3 H3C C C BrH H3C Br H CH3 C C Br H OH HBr H H3C CH3 C C Br H Br H H3C CH3 卤原子参与 Neighboring-group participation Create PDF with GO2PDF for free, if you wish to remove this line, click here to buy Virtual PDF Printer 5 C C Br H H CH3 H OH2 CH H3C Br C CH3 H Br Bror R,S-2,3-二溴丁烷 （内消旋结构） C C Br H H3C H CH3 OH2 C C Br HH H3C CH3 Br Bror R,R-和S,S-2,3-二溴丁烷 Cl-CH2CH2-S-CH2CH2-Cl 芥子气 R-S-CH2CH2-X 一个硫芥 RS-CH2CH2-Cl rate-limiting H2C CH2 S R H2O Cl fast RSCH2CH2OH2 Cl RSCH2CH2OH + HCl 硫芥和氮芥 硫原子邻位促进作用示例 S Cl HOAc S OAc + HCl CH3 C H C H2 S C2H5 OH HCl CH Cl H2 C SC2H5H3C S Cl HOAc H3C CH S CH2 Cl C2H5 R N R' CH2CH2 Cl H2O R N R' CH2CH2 OH N C2H5 CH2 Cl N Cl C2H5 H2C N CH2 R ClR' N C2H5 CH2 Cl 氮原子邻位促进作用 1 0.014 833 14 0.027 3 4 5 6 7 2 3 4 5 6 环生成的相对速率环原子数n 环的大小对环铵盐形成速率的影响 （25℃，水） Br (CH2)n NH2 (CH2)n NH2 + 环大小的效应 M.I.Page, Chem.Soc.Rev., 2,295(1973) 环的大小对环锍盐形成速率的影响 （100℃，20%的二氧六环水溶液） 1.0000 0.0053 0.2000 0.0170 0.0096 3 4 5 6 2 3 4 5 1-氯己烷 环生成的相对速率环原子数n Cl (CH2)n S (CH2)n S C6H5C6H5 + S.Winstein, J.Am.Chem.Soc.,75,147(1953) Create PDF with GO2PDF for free, if you wish to remove this line, click here to buy Virtual PDF Printer 6 对溴苯磺酸环己基酯的相对反应速率 （75℃，乙酸） 4 800 3?106 1 4.8?10-4 1.3?10-4 0.10 1.2?10-4 1.2?103 4.3?10-4 X = H X = trans-Cl cis-Cl X = trans-Br cis-Br X = trans-I cis-I ktrans/kcis反应相对速率 X OBs -OBs对溴苯磺酸基 C C H CH3 OTs H3C H HOAc CC H H3C AcO H CH3 + C C H H3C H CH3 OAc C C H H3C OTs CH3 H HOAc CC CH3 H H H3C AcO C C H CH3 OTs H3C H HOAc C CH H3C CH3 H CC H H3C AcO H CH3 + C C H H3C H CH3 OAc 芳基参与 Create PDF with GO2PDF for free, if you wish to remove this line, click here to buy Virtual PDF Printer 7 C C H H3C OTs CH3 H HOAc CC CH3 H H H3C AcO C CH H3C H CH3 C C H CH3 OTs H3C H 外消旋体 C CH H3C CH3 H S O O O C7H7 C C H H3C OAc CH3 H S，S-相同化合物 芳基的迁移 C C H CH3 OTs C2H5 H CC H CH3 H C2H5 TsO HOAc C C H C2H5 H CH3 OAc + CC H CH3 H C2H5 AcO C CH C2H5 CH3 H 涉及非经典碳正离子的邻基参与涉及非经典碳正离子的邻基参与 ClassicalClassical CarbocationCarbocation + + NonclassicalNonclassical CarbocationCarbocation CH5 + + (CH3)3C+ CH C+ CH2 CH2CH2 TsO -TsO H AcO H AcOH Ts = CH3 SO2 2电子3中心体系 1 2 35 7 4 Cl Cl- + Cl Cl � 非经典碳正离子 非经典碳正离子的产生非经典碳正离子的产生 H OTs HOAc H OAc + HOTs TsO H H OTs 溶剂解反应相对速率 实验表明： 反－7－原冰片烯基对甲苯磺酸酯 在乙酸中的溶剂解的速度比相应的饱 和化合物大 1011倍.产物构型保持. Create PDF with GO2PDF for free, if you wish to remove this line, click here to buy Virtual PDF Printer 8 非经典碳正离子中间体非经典碳正离子中间体:: CH3OH NaOCH3 NaBH4 CH3OH H OCH3 H OTs PNB = NO2 H OPNB H OPNB H3C H OPNB H3C H3C C O 1.0 13.3 148反应相对速率（140℃,二氧六环/水） X X X X k=1.0 104 1011 1014 H Cl H Br C2H5OH KOAc H OC2H5 芳香环稠合的邻位作用 H Br HOAc AgOAc H SbF6 SbF6 H OAc SbF6 Create PDF with GO2PDF for free, if you wish to remove this line, click here to buy Virtual PDF Printer 9 OBsH BsO HOBsH 2>3>1 (H3C)2C Cl (H3C)2C Cl CH H3C CH3 (H3C)2C Cl (H3C)2C Cl CH3 (H3C)2C Cl CH3H3C 1.0 17.8 157 172 37.1 相对溶解速率比较 OTsH TsO HOTsH 1 2 3 x x X Br D D D D D D H OTs HCO2H HCO2K D D D D D D H OCH O 2)σ键参与的非经典正碳离子 OAc AcOOBs HOAc H OBs endo- exo- Create PDF with GO2PDF for free, if you wish to remove this line, click here to buy Virtual PDF Printer 10 H2C H2C1 2 3 4 5 6 7 CH3COH O HOCCH3 O or 12 3 4 5 6 7 OAc AcO C CH CHH H * HOAc AcO OAc ** HC C C* * OAc * AcO + +HOAc H H H迁移 CH3 + Ph + 再如： 无d键参与部分参与 在经典的碳正离子反应中也广泛存在邻基参 与，以后各章加以讨论 返回目录 取代基效应对2-降冰片对甲苯 磺酯上exo/endo反应速率比值 X Y R R X Y exo(X = OTs, Y = H) endo(X = H, Y = OTs) exo(X = OTs, Y = H) endo(X = H, Y = OTs) R CH3 CH2Br CO2CH3 F CN kexo/kendo 181a 16a 3.7a 0.48a 0.37a H CO2CH3 CN 100b 1.2b 1.1b a：25℃,二氧六环 –水 b: 乙醇 –水 亲电加成反应 H2C CH CH2X Br+ H2C CH Br CH2 X Br H2C CH Br X CH2 Br H2C CH Br CH2 X Br H2C H C CH2 X BrBr X=OR,NHR,NH2,NR2,Cl,Br,I CH2 CH CH2I +Br2 H2C CH Br I CH2 Br H2C H C Br CH2 Br I CH2 CH CH2I Br+ H2C CH Br CH2 I Br H2C CH Br I CH2 Br H2C CH Br CH2 I Br H2C H C Br CH2 Br I Create PDF with GO2PDF for free, if you wish to remove this line, click here to buy Virtual PDF Printer 11 H2C CH CH2OR +Br2 H2C CH Br OR CH2 Br H2C H C Br CH2 Br OR H2C CH CH2OR Br+ H2C CH Br CH2 R O Br H2C CH Br OR CH2 Br H2C CH Br CH2 R O Br H2C H C Br CH2 Br OR H2C CH CH2NHR Br+ H2C CH Br CH2 HR N Br H2C CH Br NHR CH2 Br H2C CH Br CH2 HR N Br H2C H C Br CH2 Br NHR H H3C CH3 H+ + HH H3C CH3 + HH H3C CH3 OH- OH H H H3C CH3 + HH H3C CH3 OH- OH H H H3C CH3 -OOC H H COO- Cl2 Cl H H -OOC COO- C C O H O Cl H COO- C C Cl -OOC Cl H H COO- HOOC COOH H H Cl2 ClH H HOOC COOH C C HOOC Cl H H COOHCl + C C Cl HOOC H H COOH Cl COOH Br2 COOH Br +HO O Br O O Br COOH IBr O O I COOH Br2 O O Br (CH3)3C+ + CH2 C CH3 CH3 (CH3)3CCH2 C+ CH3 CH3 二 与不饱和化合物的反应 (CH3)3C++ C(CH3)3H + Create PDF with GO2PDF for free, if you wish to remove this line, click here to buy Virtual PDF Printer 12 100 % 2 6 6 100 %() 2 ( 0 0 邻位异构体） 邻位异构体 ´´= ´ == PhH PhY PhH PhY H k k k k k kf RH + R + H+R ++ 快 R+ 慢 Ingold 提出分速率因素（f）的概念，即一取代苯（PhY）进 行亲电取代反应时，环上指定位置的反应速率（ ）与 苯环（PhH）上的一个位置的反应速度（ ）的比值。 由于 所以HPhH kk 6= 6 PhH H kk = ko , km , kp kH %100 % 1 6 对位异构体 ´´= PhH PhY p k kf %100 % 2 6 间位异构体 ´´= PhH PhY m k kf同理 三 消去反应 Nu: -Hal, -OSO2Ar, -+NR3, -+SR2, -+OR2 -OCOR, -OAr, -OR, -CN -OH (-O+H2) E: H+ % Create PDF with GO2PDF for free, if you wish to remove this line, click here to buy Virtual PDF Printer 13 Mechanism Reaction kinetics:Reaction rate =k·[RNu] Substituent effects: The formation of carbocation intermediate is rate-controlling step. Carbocation intermediate is stabilized by EDGs. Ionization is favored by a good leaving group. Solvent effects: Carbocation is solvated by polar solvents of high ionizing strength. Base: Playing no role in the rate-determining step, however, bulky and stronger bases favor the E1 path over the SN1 path. Isotope effects: PKIEs for heavy-atom effects.SKIEs forβ-H effects Create PDF with GO2PDF for free, if you wish to remove this line, click here to buy Virtual PDF Printer 14 Create PDF with GO2PDF for free, if you wish to remove this line, click here to buy Virtual PDF Printer 15 Create PDF with GO2PDF for free, if you wish to remove this line, click here to buy Virtual PDF Printer 16 Create PDF with GO2PDF for free, if you wish to remove this line, click here to buy Virtual PDF Printer 17 Create PDF with GO2PDF for free, if you wish to remove this line, click here to buy Virtual PDF Printer 18 Create PDF with GO2PDF for free, if you wish to remove this line, click here to buy Virtual PDF Printer 19 四**碳正离子的重排反应----Nucleophilic Rearrangement 1 Wagner-Meerwein rearrangement H+CH3 C CH3 CH3 CH2OH H2O CH3 C CH3 CH3 CH2OH2 CH3 C CH3 CH3 CH2 H+ Cl- CH3 C CH3 CH2CH3 CH3C=CHCH3 CH3 CH3 C CH3 CH2CH3 Cl ( Carbon cation rearrangement ) Cl Cl- Cl- Cl 反应机理： 2 Demyahov重排 HNO2CH3CH2CH2NH2 CH3CHCH3 OH CH3CHCH3 Cl CH3CH CH2 H2CH2CH3C N N + -N2 CH3CH2CH2+ 1,2-亲核重排 + CH3CHCH3 + CH3CHCH3 Cl - -H+ H2O Create PDF with GO2PDF for free, if you wish to remove this line, click here to buy Virtual PDF Printer 20 N2 HNO2 CH2NH2 H+ H2O H+ CH2 + CH2OH 32% + H2O H+ OH 58% H+ 2% NH2 HNO2 N2 + + H+ H2O H+ H2O CH2=CHCH2OH 2 Pinacolic Rearrangement CH3 C CH3 OH C CH3 CH3 OH H+ H2O CH3 C CH3 OH C CH3 CH3 OH2+ CH3 C CH3 OH C CH3 CH3 + CH3 C CH3 OH C CH3 CH3 + H + CH3 C CH3 O C CH3 CH3 (CH3)2C OH C OH Ph Ph -H+ H2O(CH3)2C OH C OH Ph Ph + (CH3)2C OH C+ Ph Ph 1,2-迁移 （较稳定） C Ph Ph CH3 CH3C OH + C Ph Ph CH3 CH3C O -H+ （主要产物） The stable cation formed superior Phenyl group move first PhHC OH CHPh OH H+ PhHC CHPh OH + Ph2CH CH OH+ Ph2CH CH OH+ Create PDF with GO2PDF for free, if you wish to remove this line, click here to buy Virtual PDF Printer 21 H3C C OH Ph CH2I HgO H3C C CH2Ph -H + OH+ H3CC CH2Ph O H3C C OH CH3 C HNO2CH3 NH2 CH3 H3C C OH CH3 C -N2CH3 N CH3 N+ H3C C OH CH3 C+ CH3 CH3 -H+ H3C C +OH C CH3 CH3 CH3 H3CC C O CH3 CH3 CH3 1,2迁移 H3C C C O CH3 CH3 CH3 H+ H3C C C O H CH3 CH3 CH3 + H3C C C CH3 CH3 CH3 OH H3C C C CH3CH3 CH3 OH -H+ (CH3)3C C O CH3 (CH3)3C C O CH3 H3C C C O CH3 CH3 CH3 H+ 1 Beckmann Rearrangement C R R' N OH H+ C R R' N HO C R' R N H O C CH3 Ph N H O PCl5C Ph CH3 N OH ethyl ether Et2O, C Ph C6H4OCH3 N OH PCl5 -10 -p mp147 C C6H4OCH3 Ph N H O 171mp C Ph C6H4OCH3 N HO UV light 117mp -p-10 C C6H4OCH3 Ph N H OPCl5 Et2O, mp156 C H2O R C=NR' OH H+ R C=NR' OH2 + -H2O R'-C-NHR C=N-RR' + R'-C N-R+ H2O C=N-RR' + -H+ HO C=N-RR' O 反 应 机 理 Br N Ph O2N OH PCl5 H2O Br OO2N NHPh COOH Br O2N PhNH2 Br N Ph O2N OH PCl5 NHCOPh Br O2N H2O PhCOOH NH2 Br O2N Et2O C CH3 C N HO C2H5 H CH2C2H5 H2SO4 CH3CONH C C2H5 H CH2C2H5 Create PDF with GO2PDF for free, if you wish to remove this line, click here to buy Virtual PDF Printer 22 2 Baeyer-Villiger Rearrangement CH3 C Ph O CF3CO3H CH2Cl2 CH3 C OPh O CH3COOEtCF3CO3H O O O CH2Cl2CF3COOH O CH3 C Ph OH+ + CH3 C Ph OH CF3COOH O CH3 C Ph OH CF3C O O O H + CH3 C OPh OH + CF3COOH H+ CH3 C OPh O CH3 C CH O Ph CH3 * CH3 C OCH O Ph CH3 CHCl3 PhCO3H CF3CO3H CH2Cl2 CH3 C OC(CH3)3 O CH3 C C(CH3)3 O CF3CO3H CH2Cl2 Ph C O PhO C O CH3CH=CH2 anhydrous AlCl3 PhCH(CH3)2 PhCH(CH3)2 O2 Na2CO3/H2O 100 Ph C CH3 CH3 OOH H + PhOH CH3COCH3 3过氧化物的重排------异丙苯氧化重排 + CH3CH=CH2 AlCl3 CH(CH3)2 O2 自动氧化 -H+ O _ O CH(CH3)2 OH C-O键断裂 + (CH3)2C=OH + OH + (CH3)2C=O 质子转移 PhC CH3 CH3 O OH H + C CH3 Ph O OH2H3C + H2O_ C CH3 O PhH3C + + C CH3 O PhH3C H2O C CH3 O PhH3C OH2+ ( 95％光学纯度） 1,2-亲核重排反应的立体化学 Create PDF with GO2PDF for free, if you wish to remove this line, click here to buy Virtual PDF Printer 23 Ph H CH2NH2 Et NaNO2 HClO4,H2O OH H CH2Ph Et H HO CH2Ph Et + 键旋转 外消旋体 氢迁移 氢迁移 H3C C C CH2 + H H Nu-H3C CH C H +CH2 H3C C C CH2 H H Nu 其他重排反应 C6H5 CH C H CH2 Cl -Cl C6H5 C C CH2 Cl - + H H C6H5 C C CH2Cl H H A C C C+ +Nu - B H A B (Z) A C C C+ -Nu- B H B A (E) H+ 1,4迁移 1,2-亲核重排 -H+ CH3 CH3 OH H+ CH3 CH3 OH Create PDF with GO2PDF for free, if you wish to remove this line, click here to buy Virtual PDF Printer 24 HO CH3 H2SO4 H2+O CH3 CH3 + HO CH3 + H2SO4 CH3 OCOCH3 CH3COOH CH3 + CH3 + CH3COOH CH3 OCOCH3 + H -H+ TM OH H3+O OH OHH3C + H3C O+ H -H+ T CH3 OH + Me2CHCHO H+ H3C O OHH3C Me2CHCHOH + OHH3C + OHH OHH3C H+ -H+ OHH3C OH +H+ -H2O Ph Ph RCO3H O Ph Ph Ph Ph OH+ Ph Ph Ph O O O H Ph Ph O + RCO2H H+ Ph Ph OH + OH Ph Ph + TM CH2OH O HO 1.PhCO3H 2.HO-/H2O CH3 CH3H2SO4 CH3CHCH Br CH2 CH3CH CHCH2OCH3 CH3OH CH3 Cl CH3 + HCl Create PDF with GO2PDF for free, if you wish to remove this line, click here to buy Virtual PDF Printer 25 H2C CHCH CHCH3 + H2O H2SO4 HC CH CH OH CH3H3C CH3CH CH OCH3 + H2O HCl CH3CH2CHO +CH3OH H2C C CH3 CH2CH2CH2 C CH3 CH2 H2SO4 H3C H3C CH3 H3C CH3 H3C+ HC C OCH3 + H2O HCl CH3COCH3 O O OC2H5 O + HOC2H5 NaOH O Cl O NaOH CH3C OH CH3 CH2 CCH3 O NaOH CH3CCH3 O 2 C HO CH3 CH2CH O NaOH CCH2CHCH3 O OH O O OH OH O NaOH C OH H3C C N CH CH2 CH3CCH2CH2C O N CH3ONa O O CH3 H3C O O CH3 H3C CH3ONa Create PDF with GO2PDF for free, if you wish to remove this line, click here to buy Virtual PDF Printer