有机化学：第二章-2Structures of Alkanes and Cycloalkanes

1、Exercise1. Give IUPAC name for the following compounds: (CH3)3CCH2CH2CHCH3CH3CH3CH(CH3)22,2,5-Trimethylhexane1-Isopropyl-2-methylcyclohexane2. Draw structures corresponding to the following IUPAC name: 3-Ethyl-4,4-dimethylheptaneExerciseCis-Trans Isomerism (顺反异构顺反异构) in Cycloalkanes The common ring

2、size (C3 , C4 , C5, , C6 , C7) are severely restricted in their molecular motation.H3CHCH3HH3CHHCH3Cis-Trans isomers:cis-isomertrans-isomerRotate Cis-Trans isomers are called stereoisomers (立体异构立体异构), which have their atoms connected in the same order but differ in three-dimensional orientation (空间取

3、向空间取向). P55-57Structures of Alkanes and CycloalkanesOn the same sideOn the opposite sideStructures of Alkanes and CycloalkanesH3CCH3HHcis-1,4-DimethylcyclohexaneH3CHCH3HStructures of Alkanes and Cycloalkanes4. Conformational Isomer（构象异构体构象异构体）Conformations：The different arrangements of atoms that re

4、sult from rotation about a single bond are called conformations.Conformer: a specific conformation is called a conformational isomer.构象构象构象异构构象异构P50-51HHHHHH交叉式 (Staggered) 构象HHHHHH重叠式 (Eclipsed) 构象锯锯架架式式(Sawhorse representation)HHHHHHHHHHHH纽纽曼曼投投影影式式(Newman projection)交叉式 (Staggered) 构象重叠式 (Eclipse

5、d) 构象Structures of Alkanes and Cycloalkanes1). Conformations of Ethane （乙烷的构象乙烷的构象）H3CCH3Front carbonBack carbonConformational Analysis of EthaneStructures of Alkanes and Cycloalkanes=Stability: Staggered（交叉式交叉式 ） Eclipsed（重叠式重叠式 ） torsional strain 扭转张力扭转张力Structures of Alkanes and Cycloalkanes2). C

6、onformations of Butane（丁烷的构象丁烷的构象）Conformational Analysis of ButaneStability: 对位交叉式对位交叉式 邻位交叉式邻位交叉式 部分重叠式部分重叠式 全重叠式全重叠式 Structures of Alkanes and Cycloalkanes3). Conformations of Cyclohexane（环己烷的构象环己烷的构象） Substituted cyclohexanes are the most common cycloalkanes because of their wide occurrence in n

7、ature. For example：HOCholesterol (胆固醇胆固醇)Structures of Alkanes and Cycloalkanes Chair conformation and boat conformation are two different conformations of cyclohexane.a.角张力角张力 (angle strain)b.扭转张力扭转张力( torsional strain)c.空间张力空间张力 (steric strain)a.角张力角张力 (angle strain)b.扭转张力扭转张力( torsional strain)c.

8、空间张力空间张力 (steric strain)Structures of Alkanes and CycloalkanesAxial and equatorial bonds in cyclohexane+six axial (轴的轴的)hydrogens that are perpendicular (垂直的垂直的) to the ringaxial bonds alternate up-downsix equatorial(赤道的赤道的) hydrogens that are inthe rough plane of the ringequatorial bonds alternate

9、between sides around the ring Structures of Alkanes and Cycloalkanesa bondse bonds One chair conformation can readily interconvert to another chair conformation. The energy barrier to this interconversion is only about 45kJ/mol. This inter- conversion of chair conformations results in the exchange o

10、f axial and equatorial positions.135246123456Ring flipRing flipStructures of Alkanes and Cycloalkanes4). Conformations of substituted cyclohexanesCH3C(CH3)395%100%Structures of Alkanes and CycloalkanesStructures of Alkanes and CycloalkanesDraw the most stable conformation of: 1) 4-tert-Butyl-1-methy

11、lcyclohexane123456CH3(CH3)3C123456Structures of Alkanes and CycloalkanesDraw the most stable conformation of: 2) Cis -4-tert-Butyl-1-methylcyclohexane123456(CH3)3C(CH3)3CCH3Structures of Alkanes and CycloalkanesReview1. Sight along the C2-C3 bond of butane, draw the Newman projection of the most sta

12、ble and least stable conformationsCH3HHCH3HHHH3CHCH3HHmost stableleast stableStaggered (交叉式交叉式)Eclipsed (重叠式重叠式)ReviewName the following compound and draw the most stable conformation of it. CH3CH3C(CH3)3123456(CH3)3CCH3CH312344-tert-Butyl-1,2-dimethylcyclohexaneGeneral Formulas of Alkanes and Cyclo

13、alkanesStructures of Alkanes and Cycloalkanes.Chapter Two Saturated Hydrocarbons: Alkanes and CycloalkanesAlkanes and Cycloalkanes Physical Properties (物理性质物理性质) of Alkanes and Cycloalkanes Nomenclature of Alkanes and Cycloalkanes.Constitutional Isomers of Alkanes and Cycloalkanes Chemical Propertie

14、s of Alkanes and CycloalkanesSynthesis of Alkanes and CycloalkanesPhysical Properties of Alkanes and Cycloalkanes The physical properties of alkanes due to the presence of weak dispersion force (色散力色散力) between the molecules.Boiling Points (沸点沸点):1) show a regular increase with increasing molecular

15、weight.碳原子数目碳原子数目 数目数目，b.p2) Increased branching lowers an alkanes boiling point.碳原子数目相同碳原子数目相同支链支链，b.pThe order of boiling point: 1234(分子量分子量)Density (密度密度):Physical Properties of Alkanes and Cycloalkanes As a class, the alkanes and cycloalkanes are the least density of all groups of organic compou

16、nds, Secondary HPrimary HCH3CHCH3CH3Br2hvCl2hv1 %99 %CH3CHCH2BrCH3CH3CBrCH3CH364 %36 %CH3CHCH2ClCH3CH3CClCH3CH3Chapter Two Saturated Hydrocarbons: Alkanes and CycloalkanesSelectivity( 选择性选择性) of Halogens: I2 Br2 Cl2 F2Reactivity of Halogens: F2 Cl2 Br2 I2Chapter Two Saturated Hydrocarbons: Alkanes a

17、nd CycloalkanesConclusion: A.Reactivity of Hydrogen: Tertiary H Secondary H Primary HB.Reactivity of Halogens: F2 Cl2 Br2 I2C.Selectivity of Halogens: I2 Br2 Cl2 F2 D. Stability of free radical:CH3hvBr2CH3Br2。1。CCCH33。CChapter Two Saturated Hydrocarbons: Alkanes and Cycloalkanes Among all the isomer

18、s of C5H12 or C8H18, which molecular structure of alkanes does radical chlorination give a single monochloro product?CCH3CH3H3CCH3CCH3CH3CCH3CH3CH3CH3C5H12C8H18CCH3CH2ClH3CCH3CCH3CH3CCH3CH3CH2ClCH3Exercise2. Oxidation of Alkanes and CycloalkanesChapter Two Saturated Hydrocarbons: Alkanes and Cycloal

19、kanesCH4 + 2O2 CO2 + H2OH=-891 kJ / mol燃燃烧烧+CO2+H2OH=-3954 kJ / mol9O23. Isomeration (异构化异构化) of Alkanes and CycloalkanesCH3CH2CH2CH3Cat.CH3CHCH3CH3CH2CH3AlCl3CH3AlCl3CH3CH3+CH3CH34. Addition of small cycloalkanesChapter Two Saturated Hydrocarbons: Alkanes and Cycloalkanes+H2Ni 200oC 80oCCH3CH2CH3+H

20、2NiCH3CH2CH2CH3 300oC+H2NiCH3CH2CH2CH2CH3Difficult !a. Addition of Hydrogenb. Addition of Bromine (Br2)+Br2RTBrCH2CH2CH2Br+Br2BrCH2CH2CH2CH2BrChapter Two Saturated Hydrocarbons: Alkanes and Cycloalkanesc. Addition of Hydrogen Halide(卤代烃卤代烃) HBrBr环的破裂发生在环的破裂发生在含氢最多和含氢最少含氢最多和含氢最少的两个碳原子之间的两个碳原子之间 卤化氢的加

21、成时，卤化氢的加成时，氢加在含氢多的碳原子上，氢加在含氢多的碳原子上，卤素加在卤素加在含氢少的碳原子上含氢少的碳原子上 HBrBrChapter Two Saturated Hydrocarbons: Alkanes and CycloalkanesHomework for this chapter:P49 Problem 2.9, 2.10P70 Problem 2.46P72 Problem 2.63Demand: The title of the problems should be written in your textbook.Chapter Two Saturated Hydro

22、carbons: Alkanes and CycloalkanesAdditional problem:1. Draw the most stable chair conformation of the following molecules, (a) trans-1- Chloro-3-methylcyclohexane(b) cis-1-Ethyl-2-methylcyclohexane(c) cis-1-Bromo-4-ethylcyclohexane(d) cis-1-tert-Butyl-4-ethylcyclohexane2. Despite the limitations of

23、radical chlorination of alkanes, the reaction is still useful for synthesizing certain halogenated compounds. For which of the following compounds does radical chlorination give a single monochloro product?Chapter Two Saturated Hydrocarbons: Alkanes and Cycloalkanes(a)C2H6(b)CH3CH2CH3(c)(CH3 )3C CH2CH3(d)(e)CH3(f)CCH3CCH3spiral cycloalkanesNomenclature of Alkanes and Cycloalkanesb). Nomenclature of s