Polynuclear Hydrocarbons

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Polynuclear Hydrocarbons
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Classification of Polynuclear Hydrocarbons
Polynuclear Hydrocarbons may be divided into two
groups,
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• Polynuclear Hydrocarbons
• Benzenoid Non- Benzenoid

Isolated Fused rings
Linear Angular
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Isolated Ring Polynuclear HydrocarbonsBiphenyl
(diphenyl)
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a) Fittig reaction b) From benzene
diazonium sulphate c) From benzidine

Preparation of Biphenyl
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d) Ulmann diaryl synthesis
e) By using Arylmagnesium halide
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Reactions of biphenylBiphenyl undergoes
substitution reactions,
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In biphenyl one ring act as electron donating
group and the other act as electron withdrawing
group
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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.
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Problem Explain the
products formed when biphenyl is
mononitrated and when it is dinitrated.
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Biphenyl derivatives
(1) Benzidine (4, 4-diaminobiphenyl)
(2) Diphenic acid
(3) Diphenyl methane
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Benzidine (4, 4' diaminobiphenyl)
Methods of preparation
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From dihydrazo benzene
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Q. Show how could you prepare benzidine from
benzene?

• Answer

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Uses of Benzidine

• preparation of Congo red

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(2) Diphenic acid
Methods of preparation
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From anthranilic acid
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Ulmann diaryl synthesis
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oxidation of Phenanthrene or phenanthraquinone
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Chemical Reactions
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1. with acetic anhydride
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2. Conversion of diphenic acid to dflourenone
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3. with conc. H2SO4
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4. Oxidation of KMnO4
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5. with sodalime
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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

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

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(3) Diphenyl methane
Methods of preparation
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1. Friedel- Crafte
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2. From benzophenone
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Chemical Reactions
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1. Nitration
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2. Halogenation
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3. Oxidation
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II. Fused System
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a) Naphthalene
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Structure elucidation of naphthalene
1- Molecular Formula C6H8
2-
So naphthalene contain the skeleton
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3-
So nitro group is present in benzene ring
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4-
The benzene ring in phthalic acid produced by
oxidation of aminonaphthalene is not the same
ring is that obtained by oxidation of
nitronaphthalene.
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i.e. Naphthalene contains two benzene rings and
we can explain this by this equation
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The structure of naphthalene is confirmed by
method of its analysis
1- Howarth method
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Other way of cyclization
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• 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.

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Synthesis of 1-alkyl naphthalene
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2- From ?-benzylidene propenoic acid
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Chemical Reactions of naphthalene
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1. Reduction
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2. Oxidation
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3. Addition of Cl2
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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
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Examples of electrophilic substitution
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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
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Homonuclear attack
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Heteronuclear attack
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Examples
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Naphthalene derivatives
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1. Nitronaphthalene

• 1. naphthalene is prepared by direct nitration

• 2. naphthalene is prepared by indirect method

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2. Naphthols

• Preparation

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• Properties

1- Reaction of ? and ?- naphthols with aryl
diazonium salt
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2- Reaction of ? and ?- naphthols with nitrous
acid
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3- Conversion of ? and ?- naphthols to naphthyl
ether
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3. Naphthylamine

• Preparation
• 1- Naphthylamine

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• Preparation
• 2- Naphthylamine

Bucherer reaction
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Mechanism
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4. Halogenated naphthalene

• A) Preparation of 1- halogented naphthalene

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• B) Preparation of 2- halogenated naphthalene via
  Sandemeyer

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Questions

• Convert 2- naphthol to
• A) 2- bromonaphthol
• b) Naphthalene -2- carboxylic acid
• C) 1,2- naphthaquinone-1- oxime
• D) Ethyl ?naphthyl ether

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5. Alkyl naphthalene

• Synthesis of 1- alkyl naphthalene

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• Synthesis of 2- alkyl naphthalene

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6. Naphthaquinones

• There are six possible naphthaquinones, but only
  common are 1,2 1,4 2,6- naphthaquinones

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Preparation of naphthaquinones
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1,4- Naphthaquinone
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1,2- Naphthaquinone
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2,6- Naphthaquinone
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7. Naphthoic acid
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Preparation of 1-naphthoic acid
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From bromonaphthalene
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From 1- naphthylamine
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From 1- acetylacetophenone
2- Naphthoic acid can be prepared by the same
above methods
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Anthracene
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• Anthracene has 4 isomers

Resonance I, II are more stable, contain 2
benzene rings.
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Synthesis of anthracene

• 1. Friedl Crafts

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• 2. Elbe reaction

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• 3. From 1,4- Naphthoquinone

The above method shows presence of naphthalene in
anthracene
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• 4. From benzene and phthalic anhydride

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Chemical reactions
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• 1) Diels Alder

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• 2) Addition of one molecule of O2

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• 3) Halogenation of anthracene

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• 4) Oxidation of anthracene

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

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Anthraquinone
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Preparation
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Chemical Reactions
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• Nitration

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• Sulphonation

Anthraquinone does not undergo Friedl Craft
reaction

• Preparation of 2-amino-anthraquinone

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Alizarin
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Preparation
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Preparation of Alizarine Blue
Alizarine blue is used for dyeing wool by blue
color
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Phenanthrene
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Position of double bond
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Preparation of phenanthrene

• 1) Howrth method

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• Preparation of 1- alkyl phenanthrene

• Preparation of 2- alkyl phenanthrene

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• 2) Posher synthesis

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Chemical Reactions
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Benzil-Benzilic rearrangement
Mechanism
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Mechanism
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Phenanthraquinone

• Preparation

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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 4n2 pi electrons where n
  0,1,2,3,

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Examples
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Examples of non- benzenoid aromatic cmpound
All are aromatic( cyclic, planner,1, and agree
with Huckle rule 4n2 6 (n1)
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Examples of non- aromatic
Not aromatic both contain Sp3
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Not aromatic Does not obey Huckel rule 4n28
n1.5
Not aromatic Does not obey Huckel rule 4n24
n0.5
Aromatic cyclic, planner, obey Huckel
rule 4n22 n0
Aromatic 4n210 n2
Not Aromatic 8 pi electrons
Aromatic 4n214 n3
Aromatic 4n210 n2
Aromatic 4n210 n2