1. Polynuclear Hydrocarbons

2. Classification of Polynuclear Hydrocarbons Polynuclear Hydrocarbons may be divided into two groups,

3. Polynuclear Hydrocarbons
Benzenoid Non- Benzenoid
Isolated Fused rings
Linear Angular

4. Isolated Ring Polynuclear Hydrocarbons Biphenyl (diphenyl):

5. Preparation of Biphenyl
a) Fittig reaction b) From benzene diazonium sulphate c) From benzidine
Preparation of Biphenyl

6. d) Ulmann diaryl synthesis
e) By using Arylmagnesium halide

7. Reactions of biphenyl Biphenyl undergoes substitution reactions,

8. In biphenyl one ring act as electron donating group and the other act as electron withdrawing group

9. Resonance shows that O- and P- are the most reactive positions towards electrophilic substitution. The electrophilic substitution occurs in 4- position (major) and 2- position (minor) due to steric effect of other benzene ring. The 2nd substitution occurs in the empty ring in 2 or 4- position. e.g.

10. Problem: Explain the products formed when biphenyl is mononitrated and when it is dinitrated.

11. (1) Benzidine (4, 4`-diaminobiphenyl)
Biphenyl derivatives
(1) Benzidine (4, 4`-diaminobiphenyl)
(2) Diphenic acid
(3) Diphenyl methane

12. Benzidine (4, 4' diaminobiphenyl)
Methods of preparation

13. From dihydrazo benzene

14. Q. Show how could you prepare benzidine from benzene?
Answer

15. preparation of Congo red
Uses of Benzidine
preparation of Congo red

16. Methods of preparation
(2) Diphenic acid
Methods of preparation

17. From anthranilic acid

18. Ulmann diaryl synthesis

19. oxidation of Phenanthrene or phenanthraquinone

20. Chemical Reactions

21. 1. with acetic anhydride

22. 2. Conversion of diphenic acid to dflourenone

23. 3. with conc. H2SO4

24. 4. Oxidation of KMnO4

25. 5. with sodalime

26. Atropisomers of biphenyl
Optical isomers produced due to restricted rotation is called atropisomers
Restricted rotation produce when 0- position contains two different bulky groups and hence molecule is optically active.. for example

28. When o- position contains two similar groups, the molecule is optically inactive due to presence of plane of symmetry .. for example

29. Methods of preparation
(3) Diphenyl methane
Methods of preparation

30. 1. Friedel- Crafte

31. 2. From benzophenone

32. Chemical Reactions

33. 1. Nitration

34. 2. Halogenation

35. 3. Oxidation

36. II. Fused System

37. a) Naphthalene

38. Structure elucidation of naphthalene
1- Molecular Formula: C6H8 2-
So naphthalene contain the skeleton

39. So nitro group is present in benzene ring3-
So nitro group is present in benzene ring

40. 4-
The benzene ring in phthalic acid produced by oxidation of aminonaphthalene is not the same ring is that obtained by oxidation of nitronaphthalene.

41. i.e. Naphthalene contains two benzene rings and we can explain this by this equation

42. The structure of naphthalene is confirmed by method of its analysis
1- Howarth method

43. Other way of cyclization

44. The reaction occurs if R is o- or p- directing group such as NH2, NHR, OH, OR, R, halogen.
If R is m- directing group (e.g. NO2, CN, COOH, COCH3, SO3H) no reaction occur.
The above reaction gives  -substituted naphthalene.

45. Synthesis of 1-alkyl naphthalene

46. 2- From -benzylidene – propenoic acid

47. Chemical Reactions of naphthalene

48. 1. Reduction

49. 2. Oxidation

50. 3. Addition of Cl2

51. 4. Electrophilic substitution reaction
Q: Naphthalene udergoes electrophilic substitution at position 1 not 2. Explain
At position 1; carbocation intermediate stabilize by two resonance
So carbocation is more stable position 1 than 2

52. Examples of electrophilic substitution

54. Substituted naphthalene
Activating groups direct the electrophile to the same ring, while deactivating groups direct it to the other ring.
Elctrodonating group (EDG):
NH2, OH, OR, alkyl
Electrowithdrawing group
(EWG):
NO2, CO, COOH, CN, SO3H

55. Homonuclear attack

56. Heteronuclear attack

57. Examples:

58. Naphthalene derivatives

59. 1. Nitronaphthalene 1. naphthalene is prepared by direct nitration
2. naphthalene is prepared by indirect method

60. 2. Naphthols
Preparation:

61. Properties:
1- Reaction of  and - naphthols with aryl diazonium salt

62. 2- Reaction of  and - naphthols with nitrous acid

63. 3- Conversion of  and - naphthols to naphthyl ether

64. 3. Naphthylamine
Preparation:
1- Naphthylamine

65. Preparation:
2- Naphthylamine
Bucherer reaction

66. Mechanism

67. 4. Halogenated naphthalene
A) Preparation of 1- halogented naphthalene

68. B) Preparation of 2- halogenated naphthalene via Sandemeyer

69. Questions: Convert 2- naphthol to: A) 2- bromonaphthol
b) Naphthalene -2- carboxylic acid
C) 1,2- naphthaquinone-1- oxime
D) Ethyl –naphthyl ether

70. 5. Alkyl naphthalene
Synthesis of 1- alkyl naphthalene

71. Synthesis of 2- alkyl naphthalene

72. 6. Naphthaquinones
There are six possible naphthaquinones, but only common are 1,2; 1,4; 2,6- naphthaquinones

73. Preparation of naphthaquinones

74. 1,4- Naphthaquinone:

75. 1,2- Naphthaquinone:

76. 2,6- Naphthaquinone:

77. 7. Naphthoic acid

78. Preparation of 1-naphthoic acid

79. From bromonaphthalene

80. From 1- naphthylamine

81. From 1- acetylacetophenone
2- Naphthoic acid can be prepared by the same above methods

82. Anthracene

83. Resonance I, II are more stable, contain 2 benzene rings.
Anthracene has 4 isomers:
Resonance I, II are more stable, contain 2 benzene rings.

84. Synthesis of anthracene
1. Friedl Crafts

85. 2. Elbe reaction

86. The above method shows presence of naphthalene in anthracene
3. From 1,4- Naphthoquinone
The above method shows presence of naphthalene in anthracene

87. 4. From benzene and phthalic anhydride

88. Chemical reactions

89. 1) Diels Alder

90. 2) Addition of one molecule of O2

91. 3) Halogenation of anthracene

92. In using dil. HNO3 only to obtain 9,10- anthraquinone
4) Oxidation of anthracene
In using dil. HNO3 only to obtain 9,10- anthraquinone

93. 4) Reduction of anthracene

94. Anthraquinone

95. Preparation

97. Chemical Reactions

99. Nitration

100. Sulphonation Anthraquinone does not undergo Friedl Craft reaction
Preparation of 2-amino-anthraquinone

101. Alizarin

102. Preparation

103. Preparation of Alizarine Blue
Alizarine blue is used for dyeing wool by blue color

104. Phenanthrene

105. Position of double bond

106. Preparation of phenanthrene
1) Howrth method

107. Preparation of 1- alkyl phenanthrene:

108. 2) Posher synthesis

109. Chemical Reactions

111. Benzil-Benzilic rearrangement
Mechanism

112. Mechanism

113. Phenanthraquinone
Preparation

114. Condition necessary for aromaticity
Any compound to be aromatic, it must be;
1. Cyclic
2. Planner
3. All atoms must be SP2
4. All double bonds must be conjugated
5. Obey Huckle rule which state that any aromatic compound must contain 4n+2 pi electrons where n 0,1,2,3,…

115. Examples

116. Examples of non- benzenoid aromatic cmpound
All are aromatic( cyclic, planner,1, and agree with Huckle rule: 4n+2= 6 (n=1)

117. Examples of non- aromatic
Not aromatic; both contain Sp3

118. Does not obey Huckel rule 4n+2=8; n=1.5 Not aromatic
Aromatic; cyclic, planner,
obey Huckel rule
4n+2=2; n=0
Aromatic
4n+2=10; n=2
Not Aromatic
8 pi electrons
Aromatic
4n+2=14; n=3
Aromatic
4n+2=10; n=2
Aromatic
4n+2=10; n=2