清华大学有机化学李艳梅老师课件第4章

1、Chapter 4Cycloalkanes第四章 环烷烃Organic Chemistry A (1)By Prof. Li Yan-MeiTsinghua UniversityContent 4.1 Classification, Isomerization and nomenclature 4.2 Structure of cycloalkanes 4.3 Physical properties & spectrum data 4.4 Chemical properties 4.5 Preparation (learn on your own) 4.1 Classification, Is

2、omerization and nomenclature 4.1.1 Classification 4.1.2 Isomerism 4.1.3 Nomenclature4.1.1 ClassificationBy the size of the ring 按环的大小Small ringsMedium ringsCommon ringsLarge ringsC3C4C8C12C5C7C13By the saturation 按不饱和度CnH2nCnH2n-2CnH2n-4Cycloalkanes 环烷Cyclo olefines 环烯Cyclo alkynes 环炔Monocyclic comp

3、ounds 单环By the number of the rings 按环的数目Polyring compounds 多环Fused ring 稠环Bridged ring 桥环Spiro rings 螺环两环之间共用一个碳原子两环之间共用一根共价键（共用两个直接相连的碳原子）两环之间共用两个不直接相连的碳原子螺原子桥头碳To define the number of the rings:The number of cutting you need to get a chain molecule out of a poly ring compound几环？将桥（稠）环烃变为链状化合物时需要断裂

4、的碳链数。如需断裂两次，则为二环化合物，断裂三次则为三环化合物。Some interesting bridging compoundsCubane立方烷Primane棱 烷Diamentane金刚烷篮 烷4.1.2 Isomerism Constitutional isomers are derivated from the change of size of rings and length of side chainsC5H10环的大小及侧链长短与位置变化4.1.3 Nomenclature 命名4.1.3.1 Monocyclic alkane 单环烷烃1, When the side

5、chain is not very complicate: 当支链不复杂时，以环烷烃为母体1,2-二甲基环戊烷甲基环戊烷1-甲基-3-乙基环戊烷4-甲基-3-乙基-1-丙基环己烷2, When the side chain is complicate or difficult to name: 当支链较复杂或不易命名时，以环烷基为取代基3-cyclohexylhexane3-环己基己烷3, When two rings are connected 两环相连时Cyclopropylcyclohexane环丙基环己烷Cyclopropylcyclopropane环丙基环丙烷4, Cis and t

6、rans isomerism:Cis-1,4-dimethylcyclohexaneTrans-1,4-dimethylcyclohexaneHow to name this compound ?4.1.3.2 Polyring alkane 多环烷烃1, Spiro cycloalkanes 螺环烃1）选母体：根据成环的总碳原子数，称为“螺某烷”。2）编号：从小环开始；从第一个非螺原子开始。3）书写：先写词头“螺” 方括号内沿着编号方向写出每个环中除螺原子 外的每个环的碳原子数 数字之间用圆点隔开 最后写出包括螺原子在内碳原子数的烷烃名称 12345678910螺4.5癸烷1“小原则”：在不

7、违背螺环烃命名的“大”原则基础上，在编号时应尽可能令取代基的位号最小。123456789101-甲基螺4.5癸烷思考！spiro4.5decane螺4.5癸烷spiro5.5undecane螺5.5十一烷6-methylspiro4.5decane6-甲基4.5癸烷4-methylspiro2.4heptane4-甲基2.4庚烷1）选母体：根据成环的总碳原子数及环数，称为“n环某烷”。2）编号：从桥头碳开始；从最长桥开始。3）书写：先写环数 方括号内沿着编号方向写出每个环中除桥头碳原子 外的每个环的碳原子数 数字之间用圆点隔开 最后写出包括桥头碳原子在内碳原子数的烷烃名称 2, Bridged

8、-ring alkane and fused-ring alkane 桥环烃和稠环烃二环3.2.1辛烷2,7,7-三甲基二环2.2.1庚烷注意：有两个桥头碳可供选择二环1.2.0丁烷For polycyclic compound as following 多元环Deciding the main ring 选“主环”：最大的环Choosing the main bridged carbon 选“主桥头碳”：主环与非主环的最长桥共用的桥头碳Decide the serial number 编号：从主桥头碳开始；从最长桥开始Naming the compound 书写（注意与非主桥相连的桥需注明所

9、连桥的编号）1234567Tricyclic2.2.1.02.6heptane思考：12345678910Tricyclic3.2.2.12.7decanetricyclic3.2.2.12.7dacaneFused ringnaphthaleneHydrogenated naphthaleneEndo/exa区别：母体！ 4.2.1 Baeyers strain theory 4.2.2 Heat of combustion for cycloalkane 4.2.3 Current opinions 4.2.4 Conformations of cyclohexane 4.2.5 Conf

10、iguration of decalin4.2 Structure of cycloalkanesBefore 18801883Only penta rings and hexa rings were found. It was regarded that rings smaller than penta rings and bigger than hexa rings do not exist, or are not stable.W.H.Perkin synthesized C3, C4, and identified the relative reactivity: double bon

11、d C3 C4 ,while C5 and C6 rings are relatively more stable.1885A.von.Baeyer put forward the strain theory4.2.1 Baeyers strain theory Bayers张力学说Assumption:1, carbon atoms in the ring are on the same plane; 成环的碳原子均在同一同面上，且呈正多边形2, carbon atoms are sp3 carbon atoms; 碳原子采取sp3杂化形式，正常键角应为约109.5度3, to meet s

12、ome special angles in the ring, the bonds have to be bending; 为了满足平面正多边形的内角要求，成环的键必须向内或向外“屈挠”， “屈挠”的程度越大，体系越不稳定。More bendingMore angle strainHigher energyLess stability60o90o108o120o129oMost stable?可解释一些体系的稳定性特点，但还有一些体系无法解释。 4.2.2 Heat of combustion for cycloalkane Heat of combustion per CH2kJ/mol69

13、7686664659662658Do not fit the strain theory! 角张力（Baeyer 张力） 扭转张力 范氏力影响环体系稳定性的主要因素： 4.2.3 Current opinionsCCC105.5oCCCBent Bond （弯曲键、香蕉键）角张力：109.50-105.50=40123扭转张力：三组HCC均处于全重叠式蝴蝶状蝴蝶式1234A nonplanar conformation 非平面构象 也存在弯曲键 111.50角张力：111.50109.50 = 20部分交叉式扭转张力较小6.3kJ/mol higher全重叠式信封式 半椅式如果：具有多组全重叠

14、式Large ring多于13个碳原子的环体系中，分子链一般呈皱折形Strain energy in cycloalkanesNameAngle strainTwist strainVan de waalsC3GreatMediumNoC4GreatMediumNoC5SlightMediumNoC6NoNoNoC7C12MediumMediumGreatC12NoNoNo4.2.4 Conformations of cyclohexaneYearName of scientistPoint of view1883BaeyerAssumes that six carbon atoms are

15、on the same plane1890H.SachseTwo conformations may exist1915-1918W.M.MohrChair model and boat model1920Cyclohexane was proved to be nonplanar experimentally1943O.HasselChair model is most stable(electron diffraction method)1950D.BartonConformation analysis of cyclohexaneA history4.2.4.1 Conformation

16、 of cyclohexane250pmC350pmChair Structure 椅式123456部分交叉式，扭转张力较小Axial bondEquatorial bondTwo types of C-H bonds in chair structurea 键e 键Boat structure 船式结构183pmVan de waal radius of H atom is 120pm, so the two adjacent hydrogen atoms causes serious excluding.存在范氏力123456全重叠式，存在扭转张力2、3、5、6碳处于同一平面Flagpol

17、e interactionTwist boat structure 扭船式HHHHHHHHHHHH123456123456123456Half chair structure 半椅式Potential energy of the conformations 各种构象势能关系图46kJ/molPotential energy process 椅式构象之间的转变：46kJ/molPotential energyReaction process4.2.4.2 mono substituted cyclohexane 250pmr.t.5 95 Reason 1: Van de waals force

18、sAtomHCH2CH3NPOR/pm120200200150190140AtomSFClBrIR/pm185135180195215250pmr.t.1,3二直立键相互作用6116Reason 2: Torsional straina 键e 键6161结论与推论：1、一取代时，取代基趋向于处于e键2、若有多个取代基，在满足顺反构型关系的前提下，则越多取代基处于e键时越稳定。3、若环上有不同取代基，在满足顺反构型关系的前提下，则大基团处于e键时较稳定。4.2.4.3 double substituted cyclohexane (same groups)a 键e 键a键、e键的顺反关系Cis-

19、1,2trans-1,2trans-1,31,1cis-1,3cis-1,4trans-1,44.2.4.4 double substituted cyclohexane (different groups)Conformation with all groups on e bond is most preferred; 在满足空间构型的前提下，令尽可能多的取代基处于e键。If the above condition can not be met, the group with a bigger size is on the e bond. 优先满足大基团处于e键。-F, -CN -Cl, -

20、Br, -I -OCH3 -OH -COOH -NH2 -CH3 -CH2CH3 -CH(CH3)2 -C6H5 -C(CH3)3 注：1、OH，NH2易受溶剂的影响，尤其是形成氢键时。 2、此顺序应用于1,2取代时可能有误差。练习：画出以下结构的最稳定构象4.2.5 Configuration of decalin 十氢合萘的构型8.7kJ/mol more stable4.3 Physical properties & spectrum data物理性质： 环烷烃分子较规则，不易自由摇动 分子排列紧密 熔点、沸点、密度等一般高于相应的直链烷烃a-He-HTheoretically, e-H is 0.20.5 ppm larger than a-H . But due to the fast transform of cyclohexane, this difference is often invisible.cyclopropane0.22 cyclobutane= 1.96 other= 1.51H-NMR13C-NMRn 3 4 5 6 7 8 9 10(ppm)-2.8 23.1 26.3 2