第二周预习思考题

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？

2. 第二章 碳氢化合物Hydrocarbon

3. 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

4. 2.1 碳氢化合物的分类与命名 • 2.1.1 Classification of hydrocarbon • Alkanes and Cycloalkanes • Alkenes (cis and trans) (Z and E) • Conjugated dienes • Aromatic hydrocarbons • Alkynes

5. 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

6. 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） • Saturated 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

7. 2.1.4 Nomenclature • Common Name and Systematic Name • CH4 CH3CH3 CH3CH2CH3 • Methane Ethane Propane • CH3CH2CH2CH3 CH3CHCH3 • CH3 • C. N. n-butaneisobutane • S. N. Butane 2-methylpropane

8. 2.1.4 Nomenclature • CH3CH2CH2CH2CH3 Pentane • CH3CHCH2CH3isopentane, 2-methylbutane • CH3 • CH3 • CH3CCH3neopentane, 2,2-dimethylpropane • CH3

9. 2.1.4 Nomenclature • CH3CH2CH2CH2CH2CH3 hexane • CH3CHCH2CH2CH3 isohexane, 2-methylpentane • CH3 • CH3 • CH3CCH2 CH3neohexane, 2,2-dimethylbutane • CH3

10. 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 )

11. 2.1.4 Nomenclature (IUPAC Rules) • Systematic Name (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

12. 2.1.4 Nomenclature (IUPAC Rules) • 2. Number the chain so that the substituent gets the lowest possible number. • CH3CH2CHCH2CHCH2CH2CH3 5-ethyl-3-methyloctane • CH3 CH2CH3not 4-ethyl-6-methyloctane • because 3 < 4 • CH2CH3 • CH3CHCHCH2CH2CHCH3 3-ethyl-2,6-dimethylheptane • CH3 CH3not 5-ethyl-2,6-dimethylheptane • because 3 < 5

13. 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-dimethylhexane • CH3 CH3

14. 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 • CH3CH2CH2CHCH2CH2CHCH3 5-isopropyl-2-methyloctane • CH(CH3)2

15. 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 • CH3CH2CHCH2CHCH2CH3not • CH2CH3 5-ethyl-3-methylheptane • Cl 2-bromo-3-chlorobutane • CH3CHCHCH3not • Br 3-bromo-2-chlorobutane

16. 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 • CHCH3CHCH3 • CH3CH3 • 3-ethyl-2-methylhexane not 3-isopropylhexane • (two substituents) (one substituent)

17. 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-isobutylheptane or • 3-(1-methylethyl)hexane 4-(2-methylpropyl)heptane

18. 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

19. 2.1.4 Nomenclature (IUPAC Rules) • 2）侧链具有最低位次的链 • 2,5-dimethyl-4-(1-methylpropayl)heptane (not 3,4,5)

20. 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

21. 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

22. 2.1.4 Nomenclature (IUPAC Rules) • 7. For cycloalkane: (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

23. 2.1.4 Nomenclature (IUPAC Rules) • 2) If the ring has two different 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

24. 2.1.4 Nomenclature (IUPAC Rules) • 3) If there are more than two substituents on the ring, give the number 1 position to the 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, (2<3); not5,1,2, (4<5)

25. 以下内容请自学： • Nomenclature of Alkenes (cis and trans) • (Z and E) • Alkynes • Conjugated dienes • Aromatic hydrocarbons

26. 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

27. 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-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

28. 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 Bond in C=C: 244.8 kJ/mole • an alkyne is less reactive than an alkene • Why?（Please think it out by yourself）

29. 2.2碳氢化合物的稳定性 • Class of dienes: conjugated • isolated • cumulated • Heat of Formation:

30. 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 conjugated dienes

31. 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)

32. Questions: • Why is a conjugated diene more stable than an isolated diene? • Why is benzene a particularly stable compound?

33. 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

34. 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 delocalizedelectrons. We can draw the resonance structure: • resonance hybrid:

35. 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

37. 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 orbital on each carbon can overlap with two adjacent p orbitals. • 3. p-electrons in benzene are delocalized, we call such compound to have resonance.

38. 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。

39. 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 delocalized 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.

40. 2.3 共轭烯烃、芳香性与共振论和分子轨道理论 • Rules for Drawing Resonance Contributors • 1. Only electrons move. The nuclei of the atoms never move • 2. The only electrons that can move are π 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

41. 2.3 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 πelectrons toward a positive charge or toward a π bond

42. 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 πbond

43. 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 πbond

44. 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 not 3,3,4,7-tetramethyl-5-(1-ethylpropyl)- • 2、1-ethyl-2-mehylcyclopentane

45. 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 delocalizedelectrons. We can draw the resonance structure: • resonance hybrid:

46. 2.3 共轭烯烃、芳香性与共振论和分子轨道理论 • Aromaticity and Huckel’s Rule • Benzene ------ perticularly stable because of the resonance energy • But cyclobutadiene and cyclooctatetraene containscyclic two or four Pi-bond, they are not stable.

47. Aromaticity and Huchel’s Rule • In 1938, a German chemist Erich Huckel recognized the difference between them and generalized this obeservation into Huckel’s Rule • ------- any plannar, cyclic, conjugated system containing (4n+2) Pi electrons (where n is an integer) experiences unusual aromatic stabilization

48. Aromaticity and Huchel’s Rule • Molecular Orbital theory • ------- in benzene

49. Aromaticity and Huchel’s Rule • Molecular Orbital theory • ------- in cyclooctatetraene

50. Aromaticity and Huchel’s Rule • Other member rings