Polynuclear Aromatic Hydrocarbons
Ref. books
1. Organic Chemistry, Vol.1 - I.L. Finar
2. Organic Chemistry - Morrison a...
Polynuclear aromatic hydrocarbons are
composed by two or more benzene rings
Benzenoid Non- Benzenoid
Isolated
Polynucl...
 Benzenoid: Similar to benzene in structure or
linkage; having an aromatic ring system.
 Fused or condensed ring syste...
Naphthalene (C10H8)
Shows aromatic properties
Satisfy Huckel’s rule (4n+2)
=(4*2+2)=10
All C=C are not same (X-ray diffraction study)
C1=C2=1.36 Å
C2=C3=1.40 Å
Resonance energy of naphthalene is 61 Kcal...
Structure elucidation of naphthalene
1. Molecular Formula: C10H8
2.
So naphthalene contains the skeleton
3.
 So nitro group is present in benzene ring
4.
 The benzene ring in phthalic acid
produced by oxidation of
aminon...
 i.e. Naphthalene contains two benzene rings
and we can explain this by this equation
The structure of naphthalene is confirmed by
method of its synthesis
Howarth method
Other way of cyclization
 The reaction occurs if R is o- or p- directing
group such as NH2, NHR, OH, OR, R,
halogen.
 If R is m- directing gro...
Synthesis of 1-alkyl naphthalene
From -benzylidene – propenoic acid
Reduction
Oxidation
Addition of Cl2
Electrophilic substitution reaction
Naphthalene undergoes ES mostly at alpha-position
Resonance forms determine higher r...
At position 1; carbocation intermediate stabilize by
two resonance
So carbocation is more stable position 1 than 2
Sulfonation
 The lower stability of 1-S is attributed to the
steric interaction between the sulfonic
group and the hyd...
Substituted naphthalene
Activating groups direct the electrophile to the
same ring; i.e. Elctrodonating group (EDG):
N...
Homonuclear attack
Heteronuclear attack
Examples
Examples
Summary of naphthalene reactions
Anthracene (C14H10)
2
1
3
4
7
5
6

8 9
10

Anthracene (C14H10)
2
1
3
4
7
5
6

9 8
10

 monosubstitution (C14H9X) = 3 isomers
 Disubstitution (C14H8X...
Anthracene (C14H10)
 C1-C2 bond to have more double bond character
(shorter bond length)
 C2-C3 bond to have more sin...
Synthesis of anthracene
(i) By Friedel Crafts reaction
(a)
Synthesis of anthracene
(b)
(c)
Synthesis of anthracene
(ii) By Haworth synthesis
Synthesis of anthracene
(iii) By Diels-Alder reaction
Chemical reactions
Leaves naphthalene intact
Loss of RE=84-61=23 kcal
Attack at C-1
Attack at C-2
Chemical reactions
Attack at C-9
Leaves two benzene intact
Loss of RE=84-72 =12 kcal
Substitution product
Addition pr...
Chemical reactions
Diels Alder reaction
Addition of one molecule of O2
[HNO3+H2SO4 is not used, leads formation
of 9,10 anthraqunone by oxidation]
Phenanthrene C14H10
2
1
3
4
6
5 7
8
9
10
Phenanthrene C14H10
2
1
3
4
7
5
6
8 9
10
(C14H9X) = 5 isomers
(C14H8X2) = 25 isomers
2
1
monosubstitution
...
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/mol...
Preparation of phenanthrene
1) Howrth method
2) Posher synthesis
Preparation of 1- alkyl phenanthrene:
Preparation of 2- alkyl phenanthrene:
Oxidation:
Reduction:
 EAS in anthracene or phenanthrene yields mixtures
and is not generally useful. For example, in
sulfonation:
o m
2
1
3
4
o
m
5 6 6
4
2
1
5
3
o m
p
m o
Biphenyl methane or diphenyl methane
p
Diphenyl met...
Methods of preparation
1. Friedel- Craft
2. From benzophenone
Reactions of diphenyl methane
Nitration
Halogenation
Oxidation
Stilbene
(C6H5-CH=CH-C6H5)
Trans-stilbene
stable
m.p 125C
Cis-stilbene
unstable
m.p 5-6C
Syntheis of trans-stilbene
H2O
C6H5CHOHCH2C6H5 heat
H C6H5
C C
H
C6H5
(I)
Syntheis of trans-stilbene
(II)
C6H5CHOHCOC6H5
(III)
-Phenylcinnamic acid
Reactions of trans-stilbene
H C6H5
C6H5CH2CH2C6H5
bibenzyl
C C C6H5CHBrCHBrC6H5
H
C6H5
Br2
Stilbebe dibromide
Dph...
Synthesis of cis-stilbene
Cis-stilbebe is readily converted into trans-stilbebe
under the catalytic influence of traces...
Polynuclear aromatic hydrocarbons
Polynuclear aromatic hydrocarbons
of 54

Polynuclear aromatic hydrocarbons

Rowsan ALi
Published on: Mar 4, 2016
Published in: Education      
Source: www.slideshare.net


Transcripts - Polynuclear aromatic hydrocarbons

  • 1. Polynuclear Aromatic Hydrocarbons Ref. books 1. Organic Chemistry, Vol.1 - I.L. Finar 2. Organic Chemistry - Morrison and Boyd 3. Advanced Organic Chemistry – Bahl and Bahl 4. Organic Chemistry - Herbert Meislich
  • 2. Polynuclear aromatic hydrocarbons are composed by two or more benzene rings Benzenoid Non- Benzenoid Isolated Polynuclear Hydrocarbons Linear Fused rings Angular
  • 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. o m 2 1 3 4 Isolated ring m 5 6 6 4 2 1 5 3 o m Biphenyl or diphenyl p o m o p
  • 4. Naphthalene (C10H8) Shows aromatic properties Satisfy Huckel’s rule (4n+2) =(4*2+2)=10
  • 5. All C=C are not same (X-ray diffraction study) C1=C2=1.36 Å 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
  • 6. Structure elucidation of naphthalene 1. Molecular Formula: C10H8 2. So naphthalene contains the skeleton
  • 7. 3.  So nitro group is present in benzene ring 4.  The benzene ring in phthalic acid produced by oxidation of aminonaphthalene is not the same ring is that obtained by oxidation of nitronaphthalene.
  • 8.  i.e. Naphthalene contains two benzene rings and we can explain this by this equation
  • 9. The structure of naphthalene is confirmed by method of its synthesis Howarth method
  • 10. Other way of cyclization
  • 11.  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.
  • 12. Synthesis of 1-alkyl naphthalene
  • 13. From -benzylidene – propenoic acid
  • 14. Reduction
  • 15. Oxidation
  • 16. Addition of Cl2
  • 17. Electrophilic substitution reaction 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-1 Attack at C-2
  • 18. At position 1; carbocation intermediate stabilize by two resonance So carbocation is more stable position 1 than 2
  • 19. Sulfonation  The lower stability of 1-S is attributed to the steric interaction between the sulfonic group and the hydrogen atom in the 8-position.
  • 20. Substituted naphthalene Activating groups direct the electrophile to the same ring; i.e. Elctrodonating group (EDG): NH2, OH, OR, alkyl Deactivating groups direct it to the other ring; i.e. Electrowithdrawing group (EWG): NO2, CO, COOH, CN, SO3H
  • 21. Homonuclear attack Heteronuclear attack
  • 22. Examples
  • 23. Examples
  • 24. Summary of naphthalene reactions
  • 25. Anthracene (C14H10) 2 1 3 4 7 5 6  8 9 10 
  • 26. Anthracene (C14H10) 2 1 3 4 7 5 6  9 8 10   monosubstitution (C14H9X) = 3 isomers  Disubstitution (C14H8X2) = 15 isomers
  • 27. 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
  • 28. Synthesis of anthracene (i) By Friedel Crafts reaction (a)
  • 29. Synthesis of anthracene (b) (c)
  • 30. Synthesis of anthracene (ii) By Haworth synthesis
  • 31. Synthesis of anthracene (iii) By Diels-Alder reaction
  • 32. Chemical reactions Leaves naphthalene intact Loss of RE=84-61=23 kcal Attack at C-1 Attack at C-2
  • 33. 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
  • 34. Chemical reactions Diels Alder reaction Addition of one molecule of O2
  • 35. [HNO3+H2SO4 is not used, leads formation of 9,10 anthraqunone by oxidation]
  • 36. Phenanthrene C14H10 2 1 3 4 6 5 7 8 9 10
  • 37. Phenanthrene C14H10 2 1 3 4 7 5 6 8 9 10 (C14H9X) = 5 isomers (C14H8X2) = 25 isomers 2 1 monosubstitution Disubstitution 4 3 7 6 5 10 8 9
  • 38. 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
  • 39. Preparation of phenanthrene 1) Howrth method
  • 40. 2) Posher synthesis
  • 41. Preparation of 1- alkyl phenanthrene: Preparation of 2- alkyl phenanthrene:
  • 42. Oxidation: Reduction:
  • 43.  EAS in anthracene or phenanthrene yields mixtures and is not generally useful. For example, in sulfonation:
  • 44. o m 2 1 3 4 o m 5 6 6 4 2 1 5 3 o m p m o Biphenyl methane or diphenyl methane p Diphenyl methane (C13H12) 7
  • 45. Methods of preparation 1. Friedel- Craft 2. From benzophenone
  • 46. Reactions of diphenyl methane Nitration
  • 47. Halogenation Oxidation
  • 48. Stilbene (C6H5-CH=CH-C6H5) Trans-stilbene stable m.p 125C Cis-stilbene unstable m.p 5-6C
  • 49. Syntheis of trans-stilbene H2O C6H5CHOHCH2C6H5 heat H C6H5 C C H C6H5 (I)
  • 50. Syntheis of trans-stilbene (II) C6H5CHOHCOC6H5 (III) -Phenylcinnamic acid
  • 51. Reactions of trans-stilbene H C6H5 C6H5CH2CH2C6H5 bibenzyl C C C6H5CHBrCHBrC6H5 H C6H5 Br2 Stilbebe dibromide Dphenyl acetylene
  • 52. Synthesis of cis-stilbene Cis-stilbebe is readily converted into trans-stilbebe under the catalytic influence of traces of hydrogen bromide and peroxides