有机化学英文课件烷烃和环烷烃英文课件.ppt

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1、Alkanes and Cycloalkanes烷烃和环烷烃,Chapter 2,Section 1 Alkanes,Section 2 Cycloalkanes,Definition and Classification of Hydrocarbons,Hydrocarbon is only composed of carbon and hydrogen.,Aliphatic ,Aromatic ,Section 1 Alkanes,Structure,Nomenclature,Properties,Alkane is one kind of hydrocarbon in which all

2、 of the carbon are bound to each other and hydrogen by single (s) bonds.,. Structure,1. sp3 hybridization,C: 1s2; 2s22p2,Staut model of methane,Ball-stick model of methane,CH4 takes a tetrahedron shape.,109.5o,s-sp3 s bond by head to head overlap (see remark),sp3 hybridization and structure of metha

3、ne,Nature ofbond: symmetrical about the bond-axis; firm and not easy to break; bond can rotate around the bond-axis,CCbond formed by head to head,Ethane (CH3CH3),bond : rotate freely ； bigger overlap degree; higher stability, lower polarity.,Bonding of alkanes,All bonds are -bonds,All bond angles ar

4、e about 10928,All carbons are hybridized by sp3,Butane(C4H10),Pentane(C5H12),9,2. General formula,Homolog has similar chemical properties with different reacting rate, but their physical properties vary with the number of carbon atoms. The first member of homologous series often has special property

5、.,General formula: CnH2n+2 CH4, CH3CH3, CH3CH2CH3, CH3CH2CH2CH3,10,3. Isomerism of alkanes,Isomerism,Constitutionalisomerism,Stereo-isomerism,Carbon-chain ,Functional ,Positional ,Conformational ,Configurational ,Cis-trans ,Enantio- merism,The atoms are linked together in different way,(1) Carbon-ch

6、ain isomerism:,C5H12 :,12,Q 1 Write structural formulas or skeletal structures (simplified line structures) for the isomeric hexanes (C6H14).,13,Q 2 Identify as same or isomer the relationship between structure (a) and structure (b), (c), and (d).,A: (b) same, (c) isomer, and (d) same.,14,Classifica

7、tion of C and H,C : be grouped by the number of carbon atoms it attached.,primary carbon，1,secondary carbon，2,tertiary carbon ，3,quaternary carbon ，4,1,1,1,1,1,2,2,3,4,15,Primary H ( 1 H ): those attach to 1 carbonSecondary H ( 2 H ): those attach to 2 carbonTertiary H ( 3 H ): those attach to 3 car

8、bon,Notice:,No “ 4” H,H:,16,Which of the following compound contains 1, 2, 3and 4carbon atoms?A、2，2，3-trimethylbutaneB、2，2，3-trimethylpentane C、2，3，4-trimethylpentaneD、3，3-dimethylpentane,Answer: B,(2) Conformational isomerism,Conformational isomers of ethane,1. interconverting rapidly and easily at

9、 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) Representation of conformational isomers,represented in three ways: pe

10、rspective formula, sawhorse formula and Newman projections.,perspective formula,Sawhorse representations view the CC bond from a CC bond oblique angle.,sawhorse formula,Staggered,Eclipsed,Newman projection,Newman projection structures view the C-C bond end-on along the axis of connection.,(C) Energy

11、 analysis of conformations, the sum of Vs radiusattract each other weakly, the sum of Vs radiusrepulsion will increase greatly,lower energy,higher energy,Energy curve of ethane conformations,The low energy conformations is termed as conformer.,25,The conformation is more complex.,(D) Conformations o

12、f butane,26,Q: Which one is the most stable, which one is the least?,27,Energy curve of butane conformation,(70%),(30%),Notice:,At room temperature, butane has many conformational isomers,The most stable one is staggered,The most unstable one is eclipsed,Conclusion,The energy of four typical conform

13、ations:,in zigzag chain,30,Q: How many conformations of butane are there?A. 2 B. 4 C. 4 D. infinite,31,Nomenclature,1. Common nomenclature,n-PentaneIsopentane Neopentane,Butane butane,iso,n-,carbon atoms 6. Straight chain : normal alkanes. contains iso group (CH3)2CH-, : iso-alkane.,A chemical name

14、has 3 parts in the IUPAC system.,Parent,Prefix,Suffix,How manyCarbons?,What family?,Where; what; how many (are the substituents?),2. IUPAC nomenclature,(1) Unbranched alkanes (110):,Formula Name Formula Name CH4 methane C6H14 hexane C2H6 ethane C7H16 heptane C3H8 propane C8H18 octane C4H10 butane C9

15、H20 nonane C5H12 pentane C10H22 decane,C11H22 undecane C12H26 dodecane C13H28 tridecaneC14H30 tetradecane C15H32 pentadecane C20H42 eicosane,35,(2) Alkyl groups: ( R ),Methyl(Me),Ethyl(Et),Propyl(Pr),Isopropyl(i-Pr),Alkyl group: one H is removed from an alkane.,36,Isobutyl(i-Bu),sec-Butyl (s-butyl,s

16、-Bu),tert-Butyl (t-butyl,t-Bu),Butyl(Bu),Neopentyl,tert-Pentyl, t-Pentyl(t-amyl),37,(3) Branched alkanes:,Step 1: Find the parent. Find the longest continuous chain of carbon atoms; this chain determines the base name for the alkane.,Parent: octane,38,When two chains of equal length compete for sele

17、ction as the base chain, choose the one with more substituents.,5,6,7,Parent: heptane,x,39,Parent: heptane,Step 2: Number each carbon atom in the parent chain from the end of the chain nearest the branching .,40,Step 3: Name the alkyl groups, locate their positions by the numbers and write the name

18、as a single word, using hyphens to separate the various prefixes and commas to separate numbers. If two or more different side chains are present, list them in order of alphabet.,3-Ethyl,5-methyl,-,octane,On C-3, CH3CH2-,On C-5, CH3-,41,2,3,4-Trimethylpentane,1,2,3,4,5,If two or more identical side

19、chains are present, use di-, tri-, tetra-, and so forth,Prefixes: di=2 tri=3 tetra=4 penta=5 hexa=6 hepta=7 octa=8 nona=9 deca=10,42,3-ethyl-2,5-dimethyl-4-propylheptane,Exercise:,7 6 5 4 3 2 1,43,2,3,5-TrimethylhexaneNot 2,4,5-,3-Ethyl-6-methyloctane,44,Notice:, Prefixes: n-, sec-, tert- and iso, n

20、eo, are common names;, When alphabetizing the substitutents, some prefixes (di, tri, tetra and n-, sec-, tert- and so on) should be ignored; but some prefixes ( iso, neo, cyclo) shouldnt be ignored;, Be careful not to mix the two nomenclature systems. E.g. 2-methylisobutane is wrong.,45,Exercise:,3-

21、ethyl-4-isopropyl-3-methyl-5-propyloctane,46,Properties,2. Chemical properties of alkanes,1. Physical properties of alkanes,1. Physical properties of alkanes,36.1,Simple alkanes are colorless gases, clear liquids, or white solids, depending on their molecular weight.,(1) C1C4 gas,(2) molecular weigh

22、t , bp.,(3) branched , bp.,(4) Density and solubility. d 0.8g.mL-1 . Alkanes are hydrophobic.,C5C17 liquid, C18 solid.,bp() 36.1 27.9 9.5,mp() -129.8 -159.9-16.8,49,2. Chemical properties of alkanes,Stability: CC and CH bonds are quite strong, so alkanes are inert to many chemical reagents. Unaffect

23、ed by bases, acids, reductants, or oxidants.,Q4 Why are alkanes so inert?,A reactive site in a molecule usually has one or more unshared pairs of electrons, a polar bond, an electron-deficient atom or an atom with an expandable octet. Alkanes have none of these.,50,Substitution reaction Halogenation

24、 of alkanes,Substitution reactions,Methyl chloride,51,400450, CH4:Cl2=10:1，main product: CH3Cl.400 , CH4:Cl2=0.263:1，main product: CCl4.,52,A. Reaction mechanism,mechanism : How does the reaction take place?,chain-propagating step,chain-terminating step,hv or ,54,Other alkanes methane,The reactivity

25、 of halogenation of alkanes: F2 Cl2 Br2 I2,Methane:,violent,not iodination,55,B. Reactivity of hydrogen,Ratio of activity for 1H , 2H :,Q:,For the above reaction, how many isomeric monochlorination products will produce? The ratio?,55%,45%,56,Ratio of activityfor 1H and 3H:,Activity Order of H: 3H 2

26、H 1H CH3-H,The order of reactivity for different hydrogen atoms is:,CH4CH3CH3,+ Cl2 CH3Cl + CH3CH2Cl,hv,or,Ratio: 1 400,Why？,57,DE.,Q1: Which one 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?,59,Geometry of Alkyl Radicals,60,C. Selectivity,2/1=（97/2）（3/6）= 97/1,SUMMARY,Structure sp3 hybridization，tetrahedronIsomerism conformation: sawhorse formula F2 Cl2 Br2 I2,