第2章：碳氢化合物.ppt

1、第二周预习思考题,1、有机化合物命名的一般步骤怎样？母体如何选择？各种基团（官能团）的英文词头或词尾的变化规律如何？ 2、各种碳氢化合物的稳定性如何？芳香性与共振论是怎么回事？如何画极限共振结构式，并判断它们的能量高低？ 3、化合物结构与物理性质的关系如何？ 4、非共价弱作用力有哪些？,第二章,碳氢化合物Hydrocarbon,第二章重点讲解问题,1. 碳氢化合物的命名（以烷烃和环烷烃为例） 2. 碳氢化合物的稳定性 3. 共轭烯烃、芳香性与共振论和分子轨道理论 4. 碳氢化合物的物理性质与分子间作用力关系,2.1 碳氢化合物的分类与命名,2.1.1 Classification of hyd

2、rocarbon Alkanes and Cycloalkanes Alkenes (cis and trans) (Z and E) Conjugated dienes Aromatic hydrocarbons Alkynes,2.1 碳氢化合物的分类与命名,2.1.2 Representing Molecules Molecular formula CH4 H a Stick figure H C H a Lewis dot structure H a Sawhorse representation,2.1 碳氢化合物的分类与命名,2.1.3 通式与不饱和度（环的数目） Saturate

3、d Hydrocarbons: CnH2n+2 For a formula: CnHm Degree of unsaturated= (2n+2-m)/2 If it is a cycloalkane, the degree of unsaturated equals to the number of ring,2.1.4 Nomenclature,Common Name and Systematic Name CH4 CH3CH3 CH3CH2CH3 Methane Ethane Propane CH3CH2CH2CH3 CH3CHCH3 CH3 C. N. n-butane isobuta

4、ne S. N. Butane 2-methylpropane,2.1.4 Nomenclature,CH3CH2CH2CH2CH3 Pentane CH3CHCH2CH3 isopentane, 2-methylbutane CH3 CH3 CH3CCH3 neopentane, 2,2-dimethylpropane CH3,2.1.4 Nomenclature,CH3CH2CH2CH2CH2CH3 hexane CH3CHCH2CH2CH3 isohexane, 2-methylpentane CH3 CH3 CH3CCH2 CH3 neohexane, 2,2-dimethylbuta

5、ne CH3,2.1.4 Nomenclature,CH3CH2CHCH2CH3 none 3-methylpentane CH3 CH3CH-CHCH3 none 2,3-dimethylbutane CH3 CH3 Alkyl Group R- (replacing “ane” with “yl”) primary, secondary, tertiary, quaternary C, but only primary, secondary, tertiary H ( see our text ),2.1.4 Nomenclature (IUPAC Rules),Systematic Na

6、me (IUPAC Rules) (IUPAC: International Union of Pure and Applied Chemistry) 1. Determine the number of carbon in the longest continuous carbon chain-This chain is called the parent hydrocarbon. 1 2 3 4 5 6 7 8 CH3CH2CHCH2CH2CH2CH2CH3 3-methyl Octane CH3 CH3CHCH2CH2CH3 4-methyl Octane CH2CH2CH2CH3,2.

7、1.4 Nomenclature (IUPAC Rules),2. Number the chain so that the substituent gets the lowest possible number. CH3CH2CHCH2CHCH2CH2CH3 5-ethyl-3-methyloctane CH3 CH2CH3 not 4-ethyl-6-methyloctane because 3 4 CH2CH3 CH3CHCHCH2CH2CHCH3 3-ethyl-2,6-dimethylheptane CH3 CH3 not 5-ethyl-2,6-dimethylheptane be

8、cause 3 5,2.1.4 Nomenclature (IUPAC Rules),3. Cite the name of the alkyl substituent before the parent hydrocarbon. - A number and a word are separated by a hyphen; numbers are separated by a comma. di, tri, tetra is used to express the number of the same substituents CH3CH2CHCH2CHCH3 2,4-dimethylhe

9、xane CH3 CH3,2.1.4 Nomenclature (IUPAC Rules),And list substituents in alphabetical order. - “di, tri, tetra, sec, and tert” are ignored in alphabetizing. “iso, neo, and cyclo” are not ignored in alphabetizing. 3HC2HC CH3 CH3CH2CCH2CH2CHCHCH2CH2CH3 3,3,6-triethyl-7-methyldecane 3HC2HC CH2CH3 CH3 CH3

10、CH2CH2CHCH2CH2CHCH3 5-isopropyl-2-methyloctane CH(CH3)2,2.1.4 Nomenclature (IUPAC Rules),4. If the same substituent number are obtained in both directions, the first cited group received the lower number. CH3 3-ethyl-5-methylheptane CH3CH2CHCH2CHCH2CH3 not CH2CH3 5-ethyl-3-methylheptane Cl 2-bromo-3

11、-chlorobutane CH3CHCHCH3 not Br 3-bromo-2-chlorobutane,2.1.4 Nomenclature (IUPAC Rules),5. If a compound had two or more chains of the same length, the parent hydrocarbon is the chain with the greatest number of substituents. CH3CH2CHCH2CH2CH3 CH3CH2CHCH2CH2CH3 CHCH3 CHCH3 CH3 CH3 3-ethyl-2-methylhe

12、xane not 3-isopropylhexane (two substituents) (one substituent),2.1.4 Nomenclature (IUPAC Rules),6. If there are some complex substituents, we can use the similar method to name the substituents. CH3CH2CHCH2CH2CH3 CH3CH2CH2CHCH2CH2CH3 1 2 1 2 3 CHCH3 CH2CHCH3 CH3 CH3 3-isopropylhexane or 4-isobutylh

13、eptane or 3-(1-methylethyl)hexane 4-(2-methylpropyl)heptane,2.1.4 Nomenclature (IUPAC Rules),当一个饱和支链无环烃具有相同长度的链可作为主链时，则选择的顺序为： 1）具有侧链数目最多的链 4-propyl-2,3,5- trimethylheptane not 3-methyl-4-(1,2- dimethylpropyl)heptane,2.1.4 Nomenclature (IUPAC Rules),2）侧链具有最低位次的链 2,5-dimethyl-4-(1-methylpropayl)hepta

14、ne (not 3,4,5),2.1.4 Nomenclature (IUPAC Rules),3）在较短的侧链中，具有碳原子数目最多的链 （各侧链数分别为111288和111189） 3-ethyl- 5,9,11-trimethyl-7,7-di(2,4-dimethylhexyl)tridecane,课堂练习：,请给出上述结构的中英文IUPAC命名 1、4-(1-ethylpropyl)- 2,5,6,6-tetramethyloctane 2、1-ethyl-2-mehylcyclopentane,2.1.4 Nomenclature (IUPAC Rules),7. For cycl

15、oalkane: (skeletal structure) 1) In the case of a cycloalkane with an attached alkyl substituent, the ring is the parent hydrcarbon unless the substituent has more carbons than the ring. A. Isopropylcyclohexane B. 1-cyclobutylpentane,2.1.4 Nomenclature (IUPAC Rules),2) If the ring has two different

16、substituents, they are cited in alphabetical order and the number 1 position is given to the first cited substituent. A. 1-ethyl-3-methylcyclopentane B. 1,3-dimethylcyclohexane,2.1.4 Nomenclature (IUPAC Rules),3) If there are more than two substituents on the ring, give the number 1 position to the

17、substituent that result in a second substituent getting as low a number as possible. A. 1,1,2-trimethylcyclopentane (not 1,2,2; not 1,1,5) B. 4-ethyl-2-methyl-1-propylcyclohexane not 1,3,4, (23); not 5,1,2, (45),以下内容请自学： Nomenclature of Alkenes (cis and trans) (Z and E) Alkynes Conjugated dienes Aro

18、matic hydrocarbons,2.2 碳氢化合物的稳定性,2.2.1 Saturated hydrocarbons - Alkanes relatively stable 2.2.2 Cycloalkanes - Ring Strain Instability of three- and four-member rings - due to angle strain,2.2 碳氢化合物的稳定性,2.2.3 Alkenes - Pi Bonding The functional group is the center of reactivity of a molecule. Carbon

19、-carbon double bond (C=C) is the functional group of alkenes. Strength of Bond: C-C 347.3 kJ/mole C=C 610.9 kJ.mole a Pi Bond is weaker than a Sigma Bond,2.2 碳氢化合物的稳定性,2.2.4 Alkynes - Pi Bond Strength of Bond: C-C 347.3 kJ/mole C=C 610.9 kJ.mole C=C 836.8 kJ/mole Pi Bond in C=C: 263.6 kJ/mole Pi Bon

20、d in C=C: 244.8 kJ/mole an alkyne is less reactive than an alkene Why?（Please think it out by yourself）,2.2 碳氢化合物的稳定性,Class of dienes: conjugated isolated cumulated Heat of Formation:,2.2 碳氢化合物的稳定性,The difference between the heats reflects the difference in stability between the nonconjugated and co

21、njugated dienes,2.2 碳氢化合物的稳定性,2.2.5 Aromatic hydrocarbons Benzene, with relatively few hydrogens comparing with aliphatic compound, is a particularly stable compound because it has an unusually large resonance energy 151kJ/mole),Questions: Why is a conjugated diene more stable than an isolated diene

22、? Why is benzene a particularly stable compound?,2.3 共轭烯烃、芳香性与共振论和分子轨道理论,Conjugated Dienes 1. Single bond between C2-C3 formed by sp2-sp2 overlap, the length of the bond is shorter, therefore the bond is stronger. CH3-CH3 Csp3-Csp3 154pm CH2=CH-CH3 Csp2-Csp3 150pm CH2=CH-CH=CH2 Csp2-Csp2 146pm,2.3 共

23、轭烯烃、芳香性与共振论和分子轨道理论,2. Structure of Conjugated Dienes: 3. The conjugated diene had delocalized electrons. We can draw the resonance structure: resonance hybrid:,2.3 共轭烯烃、芳香性与共振论和分子轨道理论,分子轨道理论阐述1，3-丁二烯的结构,2.3 共轭烯烃、芳香性与共振论和分子轨道理论,Structure of Benzene 1. All the carbon are sp2 hybridized 2. The p orbita

24、l on each carbon can overlap with two adjacent p orbitals. 3. p-electrons in benzene are delocalized, we call such compound to have resonance.,2.3 共轭烯烃、芳香性与共振论和分子轨道理论,电子离域与共振 上述结构较好地表示了电子的离域，但是却无法告诉我们该结构中含有多少双键。因此化学家常用共振结构来表示。,2.3 共轭烯烃、芳香性与共振论和分子轨道理论,Some basic concepts 1. A compound with delocalize

25、d electrons is said to have resonance 2. The approximate structure using localized electrons is called a resonance contributor,a resonance structure, or a contributing resonance structure 3. The catual structure,drawn using delocalized eletrons, is called a resonance hybrid.,2.3 共轭烯烃、芳香性与共振论和分子轨道理论,

26、Rules for Drawing Resonance Contributors 1. Only electrons move. The nuclei of the atoms never move 2. The only electrons that can move are electrons and nonbonding electrons 3. The total number of electrons in the molecule does not change, neither do the numbers of paired and unpaired electrons,2.3

27、 共轭烯烃、芳香性与共振论和分子轨道理论,4. The electrons can be moved in one of the following ways 1) Move electrons toward a positive charge or toward a bond,2.3 共轭烯烃、芳香性与共振论和分子轨道理论,2) Move a nonbonding pair of electrons toward a bond,2.3 共轭烯烃、芳香性与共振论和分子轨道理论,3. Move a single nonbonding electron toward a bond,课堂练习：,请给

28、出上述结构的中英文IUPAC命名 1、4-(1-ethylpropyl)- 2,5,6,6-tetramethyloctane not 3,3,4,7-tetramethyl-5-(1-ethylpropyl)- 2、1-ethyl-2-mehylcyclopentane,2.3 共轭烯烃、芳香性与共振论和分子轨道理论,2. Structure of Conjugated Dienes: 3. The conjugated diene had delocalized electrons. We can draw the resonance structure: resonance hybrid

29、:,2.3 共轭烯烃、芳香性与共振论和分子轨道理论,Aromaticity and Huckels Rule Benzene - perticularly stable because of the resonance energy But cyclobutadiene and cyclooctatetraene containscyclic two or four Pi-bond, they are not stable.,Aromaticity and Huchels Rule,In 1938, a German chemist Erich Huckel recognized the di

30、fference between them and generalized this obeservation into Huckels Rule - any plannar, cyclic, conjugated system containing (4n+2) Pi electrons (where n is an integer) experiences unusual aromatic stabilization,Aromaticity and Huchels Rule,Molecular Orbital theory - in benzene,Aromaticity and Huchels Rule,Molecular Orbital theory - in cyclooctatetraene,Aromaticity and Huchels Rule,Other member rings,Aromaticity and Huchels Rule,Other Aromatic molecules: 1，6-桥连10-轮烯 14-轮烯，