有机化学课件Chapter 2 Alkanes and cycloalkanes

1、有机化学课件有机化学课件Chapter 2 Alkanes and cycloalkanesChapter 2 Alkanes and cycloalkanes2.1 Classes of Hydrocarbon Hydrocarbon:only hydrogen and carbon Only carbon-carbon single bonds:saturated Contain carbon-carbon multiple bonds: unsaturated Alkane:carbon atoms bonded in chainsCHHHHCH3CCH3HHCH2CH2CH2CH2CH

2、3CCHHHCCH3CH3CHCHCH2CH22.1 Classes of Hydrocarbon Cycloalkanes:carbon atoms bonded to form a ring Acyclic: not cyclic-a chain of carbon atoms Heteroatoms: not carbon and hydrogen Heterocyclic compounds:one or more heteroatoms on ring2.2 Alkanes Normal alkanes:continuous chain of carbon atoms Branche

3、d alkanes:carbon atoms bonded to more than two other carbon atoms General molecular formula:CnH2n+2 Homologous series:C4H10 and C5H12 Different CH2 number,a repeating unit Classification of Carbon AtomsCH3CH2CH2CH2CH2CH2CH2CH3octane(a normal alkane)CH3CH2CH2CH3CH3CHCH3CH3butane(normal)isobutane(bran

4、ched)2.2 Alkanes Primary carbon atom-bonded only one other carbon atom Secondary carbon atom-bonded two other carbon atoms Tertiary carbon atom-bonded three other carbon atoms Quaternary carbon atom-bonded four other carbon atoms Designated by the symbols 1, 2, 3, 42.2 Alkanes2.3 Nomenclature of Alk

5、ane Alkyl group:lost one hydrogen atom Alkane endingane Alkyl endingyl Name:prefixparentsuffix removing H givesCHHHHCHHHor CH3methanemethyl groupCCHHHHHHCCHHHHHremoving H givesor CH3CH2ethaneethyl group2.3 Nomenclature of Alkane The IUPAC rules for naming alkanes Longest,continuous,chain of carbon L

6、arge number of branch pointsCH3CH2CHCH3CH2CH3parent:5 carbons not 4CH3CHCH CH2CH2CH3CH3CH2CH3parent:6 carbons,2 branches methyl and ethyl(correct)CH3CHCH CH2CH2CH3CH3CH2CH3parent:6 carbons,1 branche three-carbon alkyl2.3 Nomenclature of Alkane Number the carbon,end of the chain,near the first branch

7、 Equal first branch,near the second branchCH3CHCH2 CHCH3CH2CH3CH2CH323456CH3CHCH2CH3CH2CHCH2CHCH3CH3CH2CH312345678carbon 2=carbon 7second branch:ethyl2.3 Nomenclature of Alkane Numberhyphenname of alkylhyphenname of alkyl+parent name,alphabetical order Di-(2),tri-(3),tetra-(4) ,same type alkyl Locat

8、ion number,seperated by commasCH3CHCH2 CHCH3CH2CH3CH2CH31234564-ethyl-2-methylhexanenot 2-methyl-4-ethylCH3CHCH2 CHCH3CH3CH2CH31234562,4-dimethylhexane2.3 Nomenclature of Alkane Prefixes di-,tri-,tetra- wont change the alphabetical order Name of alkyl groupsCH3CH2CHCH2CCH2CH2CH3CH3CH3CH2CH3123456785

9、-ethyl-3,5-dimethyloctanenot 3,5-dimethyl-5-ethyloctaneCH3CH2CH2CH3CHCH3propyl(normal propyl)isopropyl2.3 Nomenclature of AlkaneCH3CH2CH2CH2CH2CHCH3CH3butylsec-butylCH3CCH3CH3CHCH2CH3CH3iso-butyltert-butylCHCH2CH3CH3iso-butylCH3CHCH3isopropylIUPAC name1-methylethyl2-methylpropyl4-isopropylheptane =

10、4-(1-methylethyl)heptane2.4 Conformations of Alkanes About steric structure Differ in the positions of hydrogen atoms Comes from the constant rotation around carbon-carbon bond Distance of hydrogen atoms,bonding electrons Staggered:the farthest away from each other, lowest energyExtreme Conformation

11、s of Ethane Name ofConformerWedge-HatchedBond Structure Sawhorse StructureNewmanProjection 2.4 Conformations of Alkanes Eclipsed:the closest,highest energy Skew:middle of staggered and eclipsed Nemman projection formulas HHHHHHfront atomback atomNewman projection of staggered ethane conformation HHH

12、Newman projection of eclipsed ethane conformationHHBond Repulsions in Ethane 2.4 Conformations of Alkanes Conformations of butane Steric strain:repulsion of electron clouds CH3HHCH3HHanti conformation CH3HHHHCH3gauche conformationFour Conformers of Butane 2.5 Cycloalkanes Contain only carbon-carbon

13、single bond Saturated hydrocarbons, CnH2n ,single ring Geometric isomerismcyclopropane cyclobutane cyclopentane cyclohexaneHCH3HCH3CH3HHCH3Both methyl groupsare below the planeOne methyl groupis below the planecis isomertrans isomerOne methyl groupis above the plane2.5 Cycloalkanes Different spatial

14、 arrangements Nomenclature of cycloalkanes Prefix cyclo- Lower number of substituentsethylcyclopentaneisopropylcyclobutaneBrCH3CH2123456ClClCl1,1,4-trichlorocycloctanetrans-1-bromo-3-ethylcyclohexane2.6 Conformations of cycloalkanes Six-membered ring of cyclohexane Not planar,puckered conformation,

15、all CH bonds on neighboring carbon atoms:staggered Chair conformation of cyclohexane H position:axial and equatorial Ring flip:the axial and equatorial positions interchanged2.6 Conformations of cycloalkane2.6 Conformations of cycloalkane2.6 Conformations of cycloalkanes Substituted chair conformati

16、on Methylcyclohexane:a equatorial methyl is more stable than an axial methyl group Steric strain between the methyl group and the axial hydrogen atoms at the C-3 and C-5 atomsCH3Hring flipCH3Hequatorialaxial5%95%2.6 Conformations of cycloalkanes Steric strain:bulk of groups,distance of groups Equato

17、rial position:long distance Axial position:short distance2.7 Physical properties of saturated hydrocarbon Less dense than water Not polar,weak London force Not soluble in water,a polar substance The boiling points of the normal alkanes increase with increasing molecular weight Branching alkane:lower

18、 boiling point2.8 Oxidatin of alkanes and cycloalkanes Stable for oxidation Need extreme conditionsCH4+ O2CO2+ H2O2.9 Halogenation of saturated hydrocarbons Condition: high temperature or presence of light Substitution: a halogen atom in place of a hydrogen atom One and more substituted productsCH4+

19、 Cl2CH3Cl+HClchloromethane(methyl chloride)2.9 Halogenation of saturated hydrocarbons difficult to control the reactionCH3ClCl2+CH2Cl2CH2Cl2Cl2Cl2CHCl3CHCl3CCl4HClHClHCldichloromethane(methylene chloride)trichloromethane(chloroform)tetrachloromethane(carbon tetrachloride)2.9 Halogenation of saturate

20、d hydrocarbon Chlorine atom:so reactive,not seclective in its substitution for hydrogen atoms Bromine atom:not so reactive,more seclective Reactivitity:321 2-methylpropane 37% 2-chloro-2-methylpropane 63% 1 -chloro-2-methylpropane 99% 2-bromo-2-methylpropane2.9 Halogenation of saturated hydrocarbons

21、 Mechanism of chlorination Homolytic bond cleavageradical Radical:with single electron,electron deficient and highly reactiveCH3CCH3CH3H+Br2CH3CCH3CH3BrHBrCH3CCH3CH3H+Cl2CH3CCH3CH3ClHCl+CH3CCH3CH2ClH2-chloro-2-methylpropane1-dhloro-2-methylpropane(63%)(37%)2-bromo-2-methylpropane(99%)2.9 Halogenatio

22、n of saturated hydrocarbon Initial step Propagation stepsClClCl+ Clstep 1+Cl+ClCH3HCH3HClClClCH3+CH3Cl+step 2step 32.9 Halogenation of satureted hydrocarbon Chain-terminating steps+ Cl+ClClCl+ ClCH3CH3CH3CH3CH3CH3Cl3.10 Nomenclature of haloalkane Low molecular weight:name of alkyl+halide IUPAC rules Similar to alkaneCH3CH2BrCH3