The document discusses polynuclear aromatic hydrocarbons, primarily focusing on naphthalene, anthracene, and phenanthrene. It covers their definitions, structures, physical and chemical properties, as well as methods of synthesis and reactivity, highlighting the electrophilic substitution reactions and resonance energy differences among these compounds. Key aspects include the stability of their structures and the resulting isomers from substitution reactions.

1. Mr.P.S.Kore
Assistant Professor(Research Scholar)
Department of Pharmaceutical Chemistry
RCP, Kasegaon.

2. • Polynuclear Aromatic Hydrocarbon
• Definition.
• A Polynuclear aromatic hydrocarbon is
a hydrocarbon made up of fused aromatic
ring molecules. These are rings which
share one or more sides and contain
delocalized electrons.
2

3.  Benzenoid: Similar to benzene in structure or
linkage; having an aromatic ring system.
 Fused or condensed ring system: When
two rings share a pair of carbon atoms, the
rings are said to be fused rings.
2
1
3
4
665
4
2
1
5
3
Isolated ring
Biphenyl or diphenyl
o m
mo
p
o
m o
m
p

4. Fused or condensed aromatic hydrocarbons contain more
than one ring and have two carbon shared by two or more
aromatic rings.
The most important members of this class is Naphthalene,
Anthracence and Phenanthrene.
4

5. Naphthalene (C10H8)
Numbers to denote position of substituent.
Greek word alpha or beta are used to designate
two possible orientation of single substituent.
Nomenclature of Naphthalene
Para bromo
Beta bromo

6.  Structure of Naphthalene.
 All C=C are not same (X-ray diffraction study)
 C1=C2=1.36 Å Shorter than
 C2=C3=1.40 Å
 Resonance energy of naphthalene is 61 Kcal/mol
Benzene, 36 Kcal/mol
 2nd aromatic ring is less stable (61-36)=25 Kcal/mol
 Naphthalene is less aromatic (more reactive) than
benzene

8. The structure of naphthalene is confirmed by
method of its synthesis
Howarth method
Tetralin
NaphthaleneAlpha-tetralone
3-Benzoylpropanoic
acid
4-Phenylbutanoic
acid
Pd

9. Reduction

10. Physical Properties of Naphthalene
• Colorless crystalline solid.
• M.P 820c and B.P 2180c.
• Insoluble in water but dissolves in ether,
benzene, ethanol etc.
• Odour: moth ball odour.
10

11. Chemical Properties of Naphthalene
• Electrophilic substitution reactions.
• Naphthalene undergoes E+ substitution reaction.
• Substitution occurs primarily at C1 position.
• Two resonance form for the intermediate
carbonium ion obtained from the attack at C1
position.
• Only one form is possible for substitution at C2
position.
11

12. Naphthalene undergoes ES mostly at alpha-position
Resonance forms determine higher reactivity at C-1
 C-1 attack has 2 resonance structures with benzene rings
 C-2 attack has only 1 resonance structure with a benzene ring
 The most stable intermediate (C-1 attack) gives faster reaction
Attack at C-2
Attack at C-1
Electrophilic substitution reaction

13. At position 1; carbocation intermediate stabilize by
two resonance
So carbocation is more stable position 1 than 2

15. Anthracene (C14H10)
2
1
3
4
7
5
6
8 9
10



16. Anthracene (C14H10)
2
1
3
4
7
5
6
89
10


 monosubstitution (C14H9X) = 3 isomers
 Disubstitution (C14H8X2) = 15 isomers

17. Anthracene (C14H10)
 C1-C2 bond to have more double bond character
(shorter bond length)
 C2-C3 bond to have more single bond character
(longer bond length)
 From X-ray diffraction study: C1-C2 bond = 1.37 Å
C2-C3 bond = 1.42 Å
 Resonance energy 84 kcal mol-1, average 28, less
aromatic than benzene

18. Synthesis of anthracene
(i) By Friedel Crafts reaction
(a)
9,10 dihydroanthracene
(2-molecules)

19. (ii) By Haworth synthesis
Synthesis of anthracene

20. (iii) By Diels-Alder reaction
Synthesis of anthracene

21. Chemical reactions
Leaves naphthalene intact
Loss of RE=84-61=23 kcal
Attack at C-1
Attack at C-2

22. Chemical Reactions
• Attack at C9 position.
• Attack at C9 position yields a carbonium ion intermediate
in which two benzene rings are retained.
• In case of C1 and C2 position yields naphthalene.
• So C9 position yields two benzene rings(i.e. 72 kcal/mol)
where as C1 and C2 position yields naphthalene ( i.e.61
kcal/ mol) resonance energy.
• Carbonium ion intermediate can lose the proton to give
substitution product, or it can react with nucleophile to
form 9,10 addition product.
22
E
+
EH
+
+

23. Physical Properties of Anthracene
• Colourless solid
• MP-218 0C and BP- 340 0C.
• Insoluble in water, dissolves in benzene.
• It shows strong blue fluorescence when
exposed to UV light.
23

24. [HNO3+H2SO4 is not used, leads formation
of 9,10 anthraqunone by oxidation]
Reduction
Friedel-crafts acylation

25. Phenanthrene C14H10
2
1
3
4
75
6
8
9
10

26. Phenanthrene C14H10
2
1
3
4
7
5
6
8 9
10
2
1
34
7
56
10
8
9
monosubstitution
(C14H9X) = 5 isomers
Disubstitution
(C14H8X2) = 25 isomers

27. Position of double bond
2
1
3
4
7
5
6
8
9
10
 C9-C10 bond to have more double bond character
 RE 92 kcal/mole, 92-72=20 Kcal/mole to remove the
aromaticity of the middle ring

28. Preparation of phenanthrene
Haowrth method
4-(naphthalen-1-yl)-4-oxobutanoic acid
4-(naphthalen-1-yl)butanoic acid 3,4-dihydrophenanthren-1(2H)-one

29. Oxidation:
Reduction:

31.  EAS in anthracene or phenanthrene yields mixtures
and is not generally useful. For example, in
sulfonation:

32. 2
1
3
4
665
4
2
1
5
3
Biphenyl methane or diphenyl methane
o m
mo
p
o
m o
m
p
Diphenyl methane (C13H12)
7

33. Bi/Diphenyl Methane
• Diphenylmethane is an organic
compound with the formula (C6H5)2CH2.
The compound consists methane wherein
two hydrogen atoms are replaced by
two phenyl groups. Diphenylmethane
forms a common skeleton in organic
chemistry; the diphenylmethyl group is also
known as benzhydryl.
34

34. 1. Friedel- Craft
Methods of preparation
2. From benzophenone
Dichloromethane

35. Nitration

36. Halogenations
Oxidation

37. Triphenyl Methane
38

38. 39