命名, 構象分析及合成簡介 (Nomenclature, Conformational Analysis, and an Introduction to Synthesis)

Transcription

1 第 3 章烷烴 命名, 構象分析及合成簡介 (Nomenclature, Conformational Analysis, and an Introduction to Synthesis) 一 ) Introduction Alkane: C n 2n+2 Alkene: C n 2n ydrocarbon Alkyne: C n 2n-2 Cycloalkane: C n 2n Aromatic hydrocarbons...

2 Petroleum refining: Boiling Range of Number of carbon atoms Use Fractions ( o C) Below 20 C1-C4 Natural gas C5-C6 Petroleum ether C6-C7 Ligroin, solvents C5-C10 Gasoline... Nonvolatile Solide C20 and higher Paraffin wax, tar Cracking: C12 or higher catalytic cracking thermal cracking C5-C10

3 Shape and constitutional isomers of alkanes: Straight chain alkanes are also called unbranched alkanes (containing Only primary and secondary carbon atoms)

4 Branched alkanes have at least one carbon which is attached to more than two other carbons

5 Write all of the constitutional isomers with molecular formula C716 in condensed form (Page 138)

6

7 Constitutional isomers have different physical properties (melting point, boiling point, densities etc.)

8 二 ) 有機化合物的命名 (IUPAC system): to give each organic compound an unambiguous name 1) Alkane: a) unbranched-alkanes and alkyl groups:

9

10 The unbranched alkyl groups are obtained by removing one hydrogen from the alkane and named by replacing the -ane of the corresponding alkane with -yl

11 b) Branched-alkanes : 法則 1: 選擇最長的碳鏈為母體, 以烷烴的形式命名 heptane not hexane 法則 2: 單取代烷烴, 從離取代基團最近的一端開始編號, 在取代基前冠以此編號

12 法則 2: 同一碳原子有兩個烷基取代時, 編號用兩次

13 法則 4: 主鏈 (parent chain) 有兩個以上烷基取代時, 分別在每個取代基前冠以編號 取代基以英文字母順序排列 not 3-Ethyl-5-methylhexane

14 法則 5: 主鏈有相同的烷基取代時, 在同一類取代基前冠以 di-, tri-, tetra-, penta- C 2 C 3 C 3 C 2 CCC 2 CC 3 C 3 C 3 2,5-Dimethyl-4-ethylhepane The prefixes are used in alphabetical prioritization

15 法則 6: 主鏈的選擇 : 取代基最多的為優先 (When two chains of equal length compete to be parent, choose the chain with the greatest number of substituents)

16 法則 7: 兩端取代基若離主鏈末端等距離, 以使其他取代基編號最小為原則

17 Branched alkyl group: l Systematic nomenclature: 1-methylethyl Common nomenclature: isopropyl

18 2-Methyl-3-(1-Methylethyl)heptane

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20 Provide the systematic name for C511(Page 145) 3 C 2 2 C C C 2 C 2 3 C C C 2 C 2 3 C 2 C C 2 C C 3 C 3 3 C 2 C C C 2 C 3 3 C C C C 3 C 3 C 3 3 C C 2 C C 3

21 Provide the IUPAC name for C716 (Page 145)

22 2) Nomenclature of aloalkane: (Fluoro- Chloro- Iodo- Bromo-) 法則 1: 當主鏈上只有 halo 取代基時, 與烷烴的命名規則相同 Chloroethane 2-Bromopropane 法則 2: 當主鏈上有鹵代和烷基取代基時, 仍從離取代基團最近的一端開始編號, 不管是鹵代和烷基取代基 (alo and alkyl substituents are considered to be of equal ranking). Cl C 3 CCC 2 C 3 C 3 3-Chloro-2-methylpentane

23 法則 3: 若鹵代和烷基取代基離主鏈末端等距離, 以字母順序為優先編以最小 C 2 C 3 C 3 CCC 3 F Give its IUPAC name (2-Ethyl-3- fluorobutane

24 Common Functional class nomenclature:

25 Provide the IUPAC names for C49Cl and C511Br (Page 146) Cl Cl 1-Chlorobutane 1-Chloro-2-methylpropane Cl 2-Chlorobutane Cl 2-Chloro-2-methyl propane

26 Br 1-Bromopentane Br 2-Bromopentane Br Br 1-Bromo-3-methylbutane Br 1-Bromo-2-methylbutane Br Br 2-Bromo-2-methylbutane C 2 Br 1-Bromo-2,2-dimethylpropane 3-Bromopentane 2-Bromo-3-methylbutane

27 3) Nomenclature of alcohols An IUPAC name may have up to 4 features: locants, prefixes( 字頭 ), parent compound and suffixes( 字尾 )

28 IUPAC nomenclature for alcohols: 1) Select the longest chain containing the hydroxyl and change the suffix name of the corresponding parent alkane from -e to -ol 2) Number the parent to give the hydroxyl the lowest possible number 3) The other substituents take their locations accordingly

29 Provide the IUPAC names for C410O and C512O (Page 147) O 1-Butanol or Butan-1-ol O 2-Methyl-1-propanol O 2-Butanol O 2-Methyl-2-propanol

30 O O O O O 2-Methyl-2-butanol O O C 2 O 3-Methyl-2-butanol

31 Common Functional class nomenclature:

32 Alcohols with two hydroxyls are called diols in IUPAC nomenclature and glycols in common nomenclature

33 4) Nomenclature of monocyclic alkanes a) With mono alkyl and or halo substitutions: Br Bromocyclobutane Or 1-(Methylethyl)cyclohexane

34 b) With multiple alkyl and or halo substitutions: 有兩個取代基時, 編號的順序必須使得下一個取代基有較小的編號 有三個以上取代基時, 編號的順序必須使得全部取代基有較小的編號之合 C 3 C2C3 1-Ethyl-2-methylcyclopentane

35 c) With ydroxyl group d) Cycloalkyl:

36 Provide the IUPAC names for the following compounds (Page 148) ( 3 C) 3 C ( 3 C) 2 C 2 C C(C 3 ) 2 3 C 1-tert-Butyl-2-isopropylcyclopentane 1-Isobutyl-2-methylcyclohexane Cl Cl C 3 O Butylcyclohexane C 3 1-Chloro-2,4-dimethylcyclohexane 2-Chloro-cyclopentanol O C(C 3 ) 3 3-tert-Butylcyclohexanol

37 e) Bicyclic compounds:

38

39 Provide the IUPAC names for the following compounds (Page 149)

40 Cl 2-Chlorobicyclo[1,1,0]butane Bicyclo[3,2,1]octane Cl Bicyclo[2,1,1]hexane 9-Chlorobicyclo[3,3,1]nonane Bicyclo[2,2,2]octane

41 e) Alkenes and cycloalkenes: (i) For alkenes with alkyl or halo substitutions: Step 1:Alkenes are named by finding the longest chain containing the double bond and changing the name of the corresponding parent alkane from -ane to -ene Step 2:The compound is numbered to give one of the alkene carbons the lowest number

42

43 If two identical groups occur on the same side of the double bond the compound is cis If they are on opposite sides the compound is trans

44 Several alkenes have common names which are recognized by IUPAC:

45 (ii) For Cycloalkenes with alkyl or halo substitutions: The double bond of a cylcoalkene must be in position 1 and 2

46 (iii) For alkenes and cycloalkenes with -O: Compounds with double bonds and alcohol hydroxyl groups are called alkenols, the hydroxyl is the group with higher priority and must be given the lowest possible number

47

48 a) Provide the IUPAC names for the following compounds (Page 151) 3-heptene 4-Ethyl-2-methyl-1-hexene O 4-Methyl-4-penten-2-ol 2,5-Dimethyl-2-octene 1 2 3,5-Dimethylcyclohexene 1 O 2 Cl C 3 2-Chloro-3-methyl-3-cyclohexen-1-ol

49 b) Write the structures (Page 151) Br Br Cl Br Cl Cl Cl Cl

50 f) Alkynes Terminal alkyne 2 C C C 2 Pent-1-en-4-yne or 1-Penten-4-yne

51 三 ) 烷烴和環烷烴的物理性質 a) b.p. i) Boiling points of unbranched alkanes increase smoothly with number of carbons

52 ii) Branching of alkane chain lowers the boiling point.

53 b) m.p. i) For unbranched alkanes, melting points increase in an alternating pattern according to whether the number of carbon atoms in the chain is even or odd alkane chains with an even number of carbon atoms pack more closely in ii) crystalline state. For branched alkanes, the effect of chain branching on the melting points of alkanes is more difficult to predict. Generally, branching that produces highly symmetrical structures result in abnormally high melting points.

54 iii) Cycloalkanes also have much higher melting points that their open-chain counterparts. c) Density: considerably less than 1.00 g ml -1 d) Less soluble in 2 O, more soluble in organic solvents. e) eat of combustion: 使有機物完全氧化, o 之變化 C 4 + 2O 2 CO O o = -803 kj mole -1

55 四 ) 烷烴及環烷烴之構象 a) The conformation of Alkane: Conformation: The temporary molecular shapes that result from the rotation of group about single bond are called conformations of a molecule. Each possible structure is called conformer. i) Ethane:

56 Newman projection and sawhorse formula:

57 Staggered conformation and eclipsed conformation: staggered conformation: the dihedral angle between the bonds at each of the carboncarbon bond is 180 o where atoms or group bonded to carbons at each end of a carboncarbon bond are as far apart as possible.

58 eclipsed conformation Why staggered conformation of ethane is more stable than eclipsed? Staggered: electrons from a given bonding C- orbital on one carbon can be shared with an unfilled antibonding σ*orbital at the adjacent carbon yperconjugation.

59 12 kj mol-1: torsional barrier Ethane will spend most of its time in staggered conformation Many time every second, it will acquire enough energy through collisions with other molecules to surmount the torsional barrier and it will rotate through an eclipsed conformation

60 ii) Butane For the molecules like GC 2 C 2 G or the more complex, the torsinal strain includes: a) orbital consideration and b) steric hindrance

61 Gauche: the electron clouds of two methyl groups are repel each Other (3.8 kj mol-1 more than anti.

62 Only at extremely low temperature would the molecules have insufficient energies to surmount these barriers.

63 Isomer: constitutional isomer; stereoisomer (conformational isomer, cis, trans-isomers, enantiomers). Stereoisomer: 分子式和原子的連接順序相同, 但原子在空間的排列不同 Sketch a energy curve of the conformational isomers for 2-methylbutane around the C2-C3 bond (page 159)

64 C 3 3 C C C 2 2 C 3 3 C 3 C 3 C 3 3 C 3 C C 3 C 3 C 3 C 3 C 3 C 3 C 3 C 3 3 C C 3

65 b) The conformation of Cycloalkane: i) cyclopropane *Angle strain is caused by bond angles different from o *Tortional strain is caused by eclipsing C- bonds on adjacent carbons *Cyclopropane has both high angle and tortional strain

66 ii) cyclobutane *Angle strain is caused by bond angles different from o *Tortional strain is relieved by folding planar structure.

67 iii) Cyclopentane: Envelop structure *Angle strain is little if the molecule is planar (108 o ), but the tortional strain is increased. *Tortional strain is relieved by adopting envelop structure. *Cyclopentane is almost as stable as cyclohexane.

68 iv) cyclohexane: α) Chair conformation: free from angle strain as well as torsinol strain. All bond angles are o and all C- bonds are perfectly staggered. Most stable (99% molecules are estimated in a chair conformation!!) white: equatorial Red: axial 4 1

69 b) Boat conformation: free of angle strain, but not torsinol strain!!!! Flagpole interaction; van der Waals repulsion

70 Page 165 mistake!! Explain in detail

71 v) Cyclohexane with mono-substitutions: Axial hydrogens: are perpendicular to the average plane of the ring Equatorial hydrogens: lie around the perimeter of the ring x y flip x y

72 An axial methyl has an unfavorable 1,3-diaxial interaction with axial C- bonds 2 carbons away A 1,3-diaxial interaction is the equivalent of 2 gauche butane interactions

73

74 vi) Cycloalkanes with di-substitution: Cl Cl Cl cis-dichlorocyclopropane Cl trans-dichlorocyclopropane Br Br Br cis-1,3-dibromocyclobutane Br trans-1,3-dibromocyclobutane

75

76

77 disfavored di-equatorial: Favored

78 Cis-1,4-dimethylcyclohexane exists in an axial-equatorial conformation A very large tert-butyl group is required to be in the more stable equatorial position Write the structural formula of cis-isopropyl-4-methylcyclohexane (page 174)

79 C 3 3 C Name the above compounds, and analyze their conformations

80 Write the conformations of cis-1,2dimethylcyclohexane and trans- 1,2dimethylcyclohexane (page 175) C 3 C 3 C 3 C 3 C 3 C 3 C 3 C 3

81 vii) Bicyclic alkanes

82 四 ) 烷烴環烷烴的化學合成

83

84

85 Retrosynthetic Analysis-Planning Organic Synthesis The synthetic scheme is formulated working backward from the target molecule to a simple starting material Often several schemes are possible

86 Exercise: 4.19 (page 186) a) Cl Cl b) Br e) f) Cl Cl i) j) O O l) m) O n) c) g) d) h) k) o)

87 4.20 a) 3,3,4-Trimethylhexane e) 2-Bromobicyclo[3,3,1]nonane b) 2,2-Dimethyl-1- butanol c) 3,5,7-Trimethylnonane d) 3-Methyl-4-heptanol f) 2,5-Dibromo-4-ethyloctane g) Cyclobutyl-cyclopentane f) 7-Chlorobicyclo[2,2,1]heptane C C 2 3 C C O O O

88 4.22 a) C88 C C b) C612 2,2,3,3-Tetramethylbutane c) C612 Cyclohexane d) C814 1,1-Dimethylcyclobutane 1-Ethyl-1-methyl-cyclopropane Cyclopropyl-cyclopentane Cyclobutylcyclobutane Cyclooctene

89 4.23 2,2,3-Trimethylpentane , Pd/C IR, 998, 914 cm -1

90 4.25 Alkanes (C614; all possible isomers) Cl Cl Cl Cl Cl

91 4.26 Alkanes (C614; all possible isomers) Cl Cl

92 a)c712 spiro b) C 2

93 4.29: the more value of heat of combustion, the less stable of isomer 4.30: C3Br, C3C2Br, C3C2C2Br..homologous series 4.31: 4.32: Ignoring the compounds with double bond; C510 Cyclopentane Methyl-cyclobutane Ethyl-cyclopropane Dimethylcyclopropane

94 4.33: Write the structures: Cl 4.34: Omitted 4.35 omitted 4.36 a) C 3 C 3 C 3 C 3 C 3 3 C C 3 C 3 C 3 I II C 3 III C 3 3 C C 3 C 3 C 3 C 3 C 3 IV C 3 V C 3 VI C 3 C 3 I C 3 Energy: VI > II = IV > I = V > III b) omitted

95 4.37 b.p. > O > > O > Cl > 4.38 Bicyclo[1,1,0]butane 1-Butyne C 2 C 3

96 C 3 C 3 C 3 -C 3 eclipsed R C 3 C 3 C 3 -C 3 anti, more stable R R R R R R R

97 4.41: the more unstable the compounds is, the larger heat of combustion: a) cis > trans b) cis < trans c) cis > trans

98 4.42: the more stable conformation are: C 3 a) cis C 3 b) trans 3 C c) trans C 3 d) cis

99 4.43 R R R R R R R = i-pr 4.44 Br Br

100 4.45 2, Pd/C 1) N 2 Na, N 3 (l) 2) C 3 C 2 C 2 C 2 Br C 2 C 2 C 2 C 3 C 3 C 2 C 2 Br + Br Zn, Br 1) N 2 Na, N 3 (l) 2) 2, Pd/C 2,Pd/C Br Zn, Cl