Chapter 4 Cycloalkanes环烷烃

Cycloalkanes第四章环烷烃Organic Chemistry A (1)By Prof. Li Yan-MeiTsinghua UniversityContent4.1 Classification, Isomerization and nomenclature4.2 Structure of cycloalkanes4.3 Physical properties & spectrum data4.4 Chemical properties4.5 Preparation (learn on your own)4.1 Classification, Isomerization and nomenclature4.1.1 Classification4.1.2 Isomerism4.1.3 Nomenclature4.1.1 ClassificationBy the size of the ring 按环的大小Small rings Medium ringsCommon ringsLarge ringsC3~C4C8~C12C5~C7C13~By the saturation 按不饱和度C n H2n C n H2n-2 C n H2n-4Cycloalkanes 环烷Cyclo olefines 环烯Cyclo alkynes 环炔Monocyclic compounds 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几环？To define the number of the rings:The number of cutting you need to get a chain molecule out of a poly ring compound将桥（稠）环烃变为链状化合物时需要断裂的碳链数。

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 IsomerismConstitutional isomers are derivated fromthe change of size of rings and length ofside 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 chain is not very complicate: 当支链不复杂时，以环烷烃为母体methylcyclopentane2-ethyl-4-methyl-1-propylcycloheptane1-ethyl-3-methylcyclopentane1,2-dimethylcyclopentane1,2-二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 trans isomerism:CH 3CH 3HHCH 3H CH 3HCH 3CH 3CH 3CH 3Cis-1,4-dimethylcyclohexaneTrans-1,4-dimethylcyclohexaneCH3CH3CH3How 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。

123456789 101-甲基螺[4.5]癸烷思考！1 23456789 10spiro[4.5]decane 螺[4.5]癸烷spiro[5.5]undecane 螺[5.5]十一烷1 23456789 106-methylspiro[4.5]decane 6-甲基[4.5]癸烷4-methylspiro[2.4]heptane 4-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-ring alkane and fused-ring alkane 桥环烃和稠环烃12345678bicyclo[3.2.1]octane二环[3.2.1]辛烷注意：有两个桥头碳可供选择2,7,7-trimethylbicyclo[2.2.1]heptane2,7,7-三甲基二环[2.2.1]庚烷bicyclo[1.1.0]butane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连桥的编号）1234567Tricyclic[2.2.1.02.6]heptane思考：12345678910Tricyclic[3.2.2.12.7]decanetricyclic[3.2.2.12.7]dacaneFused ringnaphthalene Hydrogenatednaphthalene Endo/exaOHH endoHOHexa区别：母体！4.2 Structure of cycloalkanes4.2.1 Baeyer’s strain theory4.2.2 Heat of combustion for cycloalkane 4.2.3 Current opinions4.2.4 Conformations of cyclohexane4.2.5 Configuration of decalinBefore 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 bond > C3 >C4 ,while C5 and C6 rings are relatively more stable.1885 A.von.Baeyer put forward the strain theory4.2.1 Baeyer’s strain theory Bayer’s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 some 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 bending More angle strain Higher energyLess stability60o90o108o120o129oMoststable?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 cycloalkaneHeat ofcombustion per CH2kJ/mol 697686664659662n658 Do not fit the strain theory!影响环体系稳定性的主要因素：☐角张力（Baeyer 张力）☐扭转张力☐范氏力4.2.3 Current opinionsCC C105.5oCC CBent Bond （弯曲键、香蕉键）角张力：109.50-105.50=40 12HHHH12CH233扭转张力：三组H－C－C 均处于全重叠式蝴蝶状蝴蝶式HHHHHH H HHHHHHH HH1234A nonplanar conformation 非平面构象也存在弯曲键 111.50角张力：111.50－109.50 = 20123HHH 2C H 2CHH4部分交叉式扭转张力较小6.3kJ/mol higher 全重叠式2.5kJ/molenvelop structure half-chair structure 信封式 半椅式如果：具有多组全重叠式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 cycloalkanesName Angle strain Twist strain Van de waals C3Great Medium NoC4Great Medium NoC5Slight Medium NoC6No No NoC7~C12Medium Medium GreatC12~No No No4.2.4 Conformations of cyclohexaneA historyYear Name of scientist Point of view1883Baeyer Assumes that six carbon atoms are onthe same plane1890H.Sachse Two conformations may exist1915-1918W.M.Mohr Chair model and boat model 1920Cyclohexane was proved to benonplanar experimentally 1943O.Hassel Chair model is most stable(electron diffraction method) 1950 D.Barton Conformation analysis of cyclohexane4.2.4.1 Conformation of cyclohexane 250pmC 350pmChair Structure 椅式123456123HH H 2C C H 2H H 465H H H H 部分交叉式，扭转张力较小a 键Axial bonde 键Equatorial bondTwo types of C-H bondsin chair structureBoat structure 船式结构183pm Van de waal radius of H atom is 120pm, so the two adjacent hydrogen atoms causes serious excluding.存在范氏力123456H H H H 651H H 2C H H HH 2C 423全重叠式，存在扭转张力2、3、5、6碳处于同一平面FlagpoleinteractionTwist boat structure 扭船式H H H H H H H H H HH H 123456123456123456Half chair structure 半椅式123456123456Potential energy of the conformations 各种构象势能关系图Potential energy46kJ/molprocess椅式构象之间的转变：Potential energy46kJ/molReaction process4.2.4.2 mono substituted cyclohexaneCH 3HCH 3H250pmr.t.5 ％95 ％Reason 1: Van de waals forcesAtom H CH 2CH 3N P O R/pm 120200200150190140Atom S F Cl Br I R/pm185135180195215CH 3HCH 3H250pmr.t.1,3－二直立键相互作用6116Reason 2: Torsional strain16 2H HC C H3CH5a 键162C HHC CH3H5CH3HCH3He 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。