1、Alkanes and Cycloalkanes烷烃和环烷烃烷烃和环烷烃Chapter 2Chapter 2Cycloalkanes is only composed of carbon and hydrogen.Aliphatic Aromatic SaturatedUnsaturatedAlkenesAlkynesCH2=CH2CH CHAlicyclicCH3CH3Alkanes Alkane is one kind of hydrocarbon in which all of the carbon are bound to each other and hydrogen by sing
2、le(s s)bonds.Structure1.sp3 hybridizationC:1s2;2s22p2Basic state 2s22p2Basic state 2s22p22s12p3Excited state 2s12p32s12p3Excited state 2s12p3sp3tetrahedralshapeStaut model of methaneBall-stick model of methane CH4 takes a tetrahedron shape.109.5os-sp3 s s bond by head to head overlap(see remark)sp3
3、hybridization and structure of methane Nature ofbond:symmetrical about the bond-axis;firm and not easy to break;bond can rotate around the bond-axisCCbond formed by head to headEthane(CH3CH3)HHHHHHnear109.5oC(tetrahedral)110pm154pms s bonds bond:rotate freely；bigger overlap degree;higher stability,l
4、ower polarity.Bonding of alkaneslAll bonds are-bondslAll bond angles are about 10928lAll carbons are hybridized by sp392.General formulaGeneral formula:CnH2n+2 CH4,CH3CH3,CH3CH2CH3,CH3CH2CH2CH310IsomerismConstitutionalisomerismStereo-isomerismCarbon-chain Functional Positional Conformational Configu
5、rational Cis-trans Enantio-merismThe atoms are linked together in different way(1)Carbon-chain isomerism:n-Pentaneiso-Pentaneneo-PentaneC5H12:CH3CH3CH3CH2CH2CH2CH3CH3CHCH2CH3 CH3-C-CH3CH3CH3CH3CH3CH2CH2CH2CH3CH3CHCH2CH3 CH3-C-CH3CH312 Write structural formulas or skeletal structures(simplified line
6、structures)for the isomeric hexanes(C6H14).CH3CHCH2CH2CH3CH3CH3CH2CHCH2CH3CH3CH3CHCHCH3CH3CH3CCH2CH3CH3CH3CH3CH3CH2CH2CH2CH2CH313 Identify as same or isomer the relationship between structure(a)and structure(b),(c),and(d).CH3CHCH2CHCH2CH3CH3CH3(a)CH2CHCH2CHCH3CH3CH3CH3(b)CH3CHCHCH2CH2CH3CH3CH3CH3CHC
7、H2CHCH3CH3CH2CH3(c)(d)(b)same,(c)isomer,and(d)same.14Classification of C and HC be grouped by the number of carbon atoms it attached.primary carbon，1secondary carbon，2tertiary carbon，3quaternary carbon，4CH3CH2CHCH2CCH3CH3CH3CH315Primary H (1 H):those attach to 1 carbonSecondary H (2 H):those attach
8、to 2 carbonTertiary H (3 H):those attach to 3 carbonCH3CH2CHCH2CCH3CH3CH3CH3123241111Notice:No“4”HH:16nWhich of the following compound contains 1,2,3and 4carbon atoms?nA、2，2，3-trimethylbutanenB、2，2，3-trimethylpentane nC、2，3，4-trimethylpentanenD、3，3-dimethylpentaneAnswer:B(2)Conformational isomerismC
9、onformational isomers of ethane1.interconverting rapidly and easily at room temperature.2.an infinite number of conformations of ethane.3.very little difference in physical properties,but probably great difference of some molecules in biochemistry.(A)The characteristics of conformations(B)Representa
10、tion of conformational isomersrepresented in three ways:perspective formula,sawhorse formula and Newman projections.HHHHHHHHHHHHperspective formulaSawhorse representations view the CC bond from a CC bond oblique angle.sawhorse formulaStaggeredEclipsedNewman projection Newman projection structures vi
11、ew the C-C bond end-on along the axis of connection.227289249306(C)Energy analysis of conformations the sum of Vs radiusattract each other weakly the sum of Vs radiusrepulsion will increase greatlylower energyhigher energyThe low energy conformations is termed as.25The conformation is more complex.(
12、D)Conformations of butane26Q:Which one is the most stable,which one is the least?2760120018024030036019kJ.mol16kJ.mol3.8kJ.molpotential energyCH3HH3CHHCH3HHHHHH3CHHHHCH3CH3HHHHCH3H3CHHHHCH3CH3HHHHCH3CH3HHCH3CH3HHRotationFigure 2.5 Energy changes that arise from rotation of the C2-C3 bond of butaneAn
13、tiAntiGaucheGauche EclipsedEclipsedEclipsed1116kJ.mol11(70%)(30%)lAt room temperature,butane has many conformational isomerslThe most stable one is staggeredlThe most unstable one is eclipsedThe energy of four typical conformations:Anti-conformationGouche conformationEclipsed(partial)conformationEcl
14、ipsed conformation4 D.infinite31CH3CH3CH2CH2CH2CH3CH3CHCH2CH3CH3-C-CH3CH3CH3CH3CH3CH2CH2CH2CH3CH3CHCH2CH3CH3-C-CH3CH3CH31.Common nomenclaturen-PentaneIsopentane NeopentaneButane butaneCH3CH2CH2CH3 CH3CHCH3CH3ison-carbon atoms CH2Cl2 +HClDichloromethanehv or heatCH2Cl2 +Cl2 CHCl3 +HClTrichloromethane
15、hv or heatCHCl3 +Cl2 CCl4 +HClTetrachloridehv or heat400450,CH4:Cl2=10:1，main product:CH3Cl.400,CH4:Cl2=0.263:1，main product:CCl4.52Free radical chain reaction :does the reaction take place?Cl：ClCl+Cl热或光CH3H +ClCH3+HClCH3+Cl2Cl+CH3ClCH3Cl +Cl CH2Cl +HCl CH2Cl +Cl2 CH2Cl2 +ClCH2Cl2 +Cl CHCl2 +HCl CHC
16、l2 +Cl2 CHCl3 +Cl CHCl3 +Cl CCl3 +HCl CCl3 +Cl2 CCl4 +Clchain-terminating stepCl+Cl Cl2CH3+CH3 CH3CH3CH3+Cl CH3Clhv or 54Other alkanes methaneThe reactivity of halogenation of alkanes:F2 Cl2 Br2 I2Methane:violentnot iodination55Ratio of activity for 1H,2H:Q:1H2H=45%/655%/2=141H2H=45%/655%/2=14For th
17、e above reaction,how many isomeric monochlorination products will produce?The ratio?55%45%5663%37%CH3CHCH3CH3hvCH3CHCH2ClCH3+Cl2CH3CCH3ClCH3Ratio of activityfor 1H and 3H:Activity Order of H:3H 2H 1H CH3-HThe order of reactivity for different hydrogen atoms is:1H3H=63%/937%/1=151H3H=63%/937%/1=15CH4
18、CH3CH3+Cl2 CH3Cl +CH3CH2ClhvorRatio:1 40057CH3-H CH3+HCH3CH2-H CH3CH2+H(CH3)2CH-H (CH3)2CH +H(CH3)3C-H (CH3)3C +H离解能:435kJ mol-1离解能:410kJ mol-1离解能:397kJ mol-1 离解能:385kJ mol-1 DE.E CH3H RCH2H R2CHH R3CHCH3RCH2R2CHR3CH=435kJ/molH=393H=406H=379CRRRCRRHCHRHCHHHTertiarySecondaryPrimaryMethylQ1:Which one
19、is the most stable?（）A、CH3 B、(CH3)3C C、CH3CH2CH2 D、(CH3)2CH Q2:What hybridization does the methyl free radical(CH3)adopt?How many electrons are there in its 2p orbital?0,1 or 2?5960CCH3H3CCH3HBr2CCH3H3CCH3BrCCH3H3CCH2BrH99%tracehv+2/1=（97/2）（3/6）=97/1CH3-CH3+Br2hv，127 CH3CH2-Br+HBrCH3-CH3+Br2hv，127 CH3CH2-Br+HBrCH3CH2CH3Br2 hv，127 CH3CH2CH2-Br+CH3CHCH3Br(3%)(97%)CH3CH2CH3Br2 hv，127 CH3CH2CH2-Br+CH3CHCH3Br(3%)(97%)1.Structure sp3 hybridization，tetrahedron conformation:sawhorse formula&Newman projection IUPAC name:3 steps Free radical substitution and
