POLYNUCLEAR AROMATIC HYDROCARBONS

B.PHARM 3RD SEM ORGANIC VHEMISTRY UNIT 4

1. POLY AROMATIC
HYDROCARBONS
Made by-PRIYANSHA SINGH
Roll No.-1738
UNIVERSITY INSTITUTE OF PHARMACEUTICAL SCIENCES
PANJAB UNIVERSITY

2. Isolated
Linear
Polynuclear Hydrocarbons
Benzenoid
Non-Benzenoid
Fused rings
Angular
Poly-nucleararomatichydrocarbonsarecomposed
bytwoormorebenzenerings

3. Benzenoid:Similartobenzeneinstructureor
linkage;havinganaromaticringsystem.
Fusedorcondensedringsystem:When
tworingsshareapairofcarbonatoms,the
ringsaresaidtobefusedrings.
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. NAPTHALENE(C
10H
8)
Shows aromatic properties
Satisfy Huckel’s rule (4n+2)
=(4*2+2)=10

5. All C=C are not same (X-ray diffraction study)
C
1=C
2=1.36 Å
C
2=C
3=1.40 Å
Resonance energy of naphthalene is 61 Kcal/mol
Benzene, 36 Kcal/mol
2ndaromaticringislessstable(61-36)=25
Kcal/mol
Naphthaleneislessaromatic(morereactive)than
benzenebecauseithaslessresonancestabilizing
energyascomparedto2individualbenzene
molecules.

6. Structure elucidation of naphthalene
1.MolecularFormula:C
10H
8
2.
So naphthalene contains the skeleton

7. So nitro group is present in benzene ring.
Nitration basically means reaction with
HNO3/H2SO4
3.
4.
Thebenzeneringinphthalicacid
producedbyoxidationofamino-
naphthaleneisnotthesameringis
thatobtainedbyoxidationofnitro
naphthalene.

8. i.e.Naphthalenecontainstwobenzenerings
andwecanexplainthisbythisequation

9. Thestructureofnaphthaleneisconfirmedby
methodofitssynthesis
Howarthmethod

10. Other way of cyclization

11. ThereactionoccursifRiso-orp-directing
groupsuchasNH
2,NHR,OH,OR,R,halogen.
IfRism-directinggroup(e.g.NO
2,CN,COOH,
COCH
3,SO
3H)noreactionoccur.
Theabovereactiongives-substituted
naphthalene.

12. Synthesis of 1-alkyl naphthalene

13. From -benzylidene –propenoic acid

14. Reduction

15. Oxidation

16. Addition of Cl
2/ Br
2

17. NaphthaleneundergoesESmostlyatalpha-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

18. Atposition1;carbocationintermediatestabilizebytwo
resonancewithinonebenzenering.
Socarbocationismorestableposition1than2

20. Thelowerstabilityof1-Sisattributedtothe
stericinteractionbetweenthesulfonic
groupandthehydrogenatominthe
8-position.
Sulfonation

21. Summary of naphthalene reactions

22. Medicinal uses of Naphthalene
Preparation of beta blocker drugs.
To synthesize synthetic dyes.
Useful insecticide.
Veterinary medicine –dusting powder.
Polyethylene naphthalene to prepare plastic bottles.
Naphthalene sulfonic acids are used to prepare plasticizers,
natural rubbers etc.
Naphthalene drugs to cure cough, urine infection, eye
trouble etc.

23. Anthracene (C
14H
10)
2
1
3
4
7
5
6
8 9
10



24. Anthracene (C
14H
10)
2
1
3
4
7
5
6
89
10


monosubstitution (C
14H
9X) = 3 isomers
Disubstitution (C
14H
8X
2) = 15 isomers

25. Anthracene (C
14H
10)
C
1-C
2bondtohavemoredoublebondcharacter
(shorterbondlength)
C
2-C
3bondtohavemoresinglebondcharacter
(longerbondlength)
FromX-raydiffractionstudy:C
1-C
2bond=1.37Å
C
2-C
3bond=1.42Å
Resonanceenergy84kcalmol
-1
,average28,less
aromaticthanbenzene

26. Synthesis of Anthracene
(i) By Friedel Crafts reaction
(a)

27. Synthesis of Anthracene
(b)
(c)

28. Synthesis of Anthracene
(ii) By Haworth synthesis

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

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

31. Chemical reactions
Attack at C-9
Leaves two benzene intact
Loss of RE=84-72 =12 kcal
Substitution product
Addition product
Reactions preferentially occur at C-9 & C-10

32. Chemical reactions
Diels Alder reaction
Addition of one molecule of O
2

33. [HNO
3+H
2SO
4is not used, leads formation
of 9,10 anthraqunone by oxidation]

34. Medicinal uses of Anthracene
Anthracene glycosides are oxygenated derivatives of
pharmacological importance that are used as laxatives or
cathartics, antineoplastic agent, polycystic kidney.
Anti-inflammatory, antibacterial, antifungal and anti-
proliferative activity.
As natural dyes.
Hepato-protective, nephron-protrctive, antioxidant.

35. Phenanthrene C
14H
10
2
1
3
4
75
6
8
9
10

36. Phenanthrene C
14H
10
2
1
3
4
7
5
6
8 9
10
2
1
34
7
56
10
8
9
monosubstitution
(C
14H
9X) = 5 isomers
Disubstitution
(C
14H
8X
2) = 25 isomers

37. Position of double bond
2
1
3
4
7
5
6
8
9
10
C
9-C
10bondtohavemoredoublebondcharacter
RE92kcal/mole,92-72=20Kcal/moletoremovethe
aromaticityofthemiddlering

38. Preparation of phenanthrene
1) Howrth method

39. 2) Posher synthesis

40. Preparation of 2-alkyl phenanthrene:
Preparation of 1-alkyl phenanthrene:

41. Oxidation:
Reduction:

43. EASinanthraceneorphenanthreneyieldsmixtures
andisnotgenerallyuseful.Forexample,in
sulfonation:

44. Medicinal uses of
Phenanthrene
Steroid moiety contain phenanthrene nucleus which is
present in sex hormones
Codeine has phenanthrene moiety
44

45. 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 (C
13H
12)
7

46. 1. Friedel-Crafte
Methods of preparation
2. From benzophenone

47. Nitration

48. Halogenation
Oxidation

49. Stilbene
Trans-stilbebe
stable
Cis-stilbebe
unstable
(C
6H
5-CH=CH-C
6H
5)

50. C
6H
5CHOHCH
2C
6H
5
Syntheis of trans-stilbene
(I)

51. Syntheis of trans-stilbene
C
6H
5CHOHCOC
6H
5
(II)
(III)
-Phenylcinnamic acid

52. Reactions of trans-stilbene
C
6H
5CH
2CH
2C
6H
5
Stilbebe dibromide
bibenzyl
Dphenyl acetylene

53. Synthesis of cis-stilbene
Cis-stilbebeisreadilyconvertedintotrans-
stilbebeunderthecatalyticinfluenceoftracesof
hydrogenbromideandperoxides

54. Triphenylmethane
Triphenylmethane (C6H6)3CH is the chromogen of a large
number of dyes. The common chromophore is the p-
quinoid structure and the auxochromes are OH,NH2 and
NR2.
Triphenylmethane dyes are very brilliant intense colors but
fade quickly in light. Therefore, they are no longer much
used on textiles. However, they are used in large quantities
for coloring paper and typewriter ribbons.
Synthesis:-
Derivatives examples-crystal violet, malachite green
54