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Study material related to the title of the above University level Study material of biochemistry All the best for your prospects
Typology: Study notes
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Azulene
Biphenyl
Naphthalene
Phenanthrene
Polynuclear Hydrocarbons
Benzenoid
Non- Benzenoid
Polynuclear aromatic hydrocarbons are
composed by two or more benzene rings
8 1
2
3
4
5
6
7
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
2nd aromatic ring is less stable (61-36)=
Kcal/mol
Naphthalene is less aromatic (more reactive)
than benzene
Nitrophthalic acid
2
O
Phthalic acid
COOH
COOH
nitration
redn.
i.e. Naphthalene contains two benzene rings
and we can explain this by this equation
2
2
A B
A
3
2
Other way of cyclization
R
O
O
O
AlCl
3
R
O
O
HO
Succinic anhydride
R
O
Cl
SOCl
2
R
O
intramoluclar
AlCl
3
Friedel Craf t
Zn-Hg/HCl
R
Se
R
The reaction occurs if R is o - or p - directing
group such as NH
2
, NHR, OH, OR, R,
halogen.
If R is m - directing group (e.g. NO
2
, CN,
COOH, COCH
3
, SO
3
H) no reaction occur.
The above reaction gives -substituted
naphthalene.
From -benzylidene – propenoic acid
naphthalene
conc. H
2
4
2
Benzylidene- 3 - propenoic acid
2
1 , 4 - dichloro- 1 , 4 - dihydronaphthalene
2
Cl
2
Naphthalene undergoes ES mostly at alpha-position
Attack at C-
Attack at C-
Electrophilic substitution reaction
Naphthalene
naphthalene- 1 - sulfonic acid
Cl
2
SO
3
H
Cl
1 - chloronaphthalene
NO
2
conc. HNO 3
conc. H
2
SO
4
1 - nitronaphthalene
conc. H
2
SO
4
40 ° C
conc. H 2
SO 4
180 ° C
SO
3
H
naphthalene- 2 - sulfonic acid
FeCl
3
CH
3
COCl
AlCl 3
CS 2
COCH
3
1 - Acetylnaphthalene
CH 3
COCl
AlCl 3
PhNO 2
COCH
3
2 - Acetylnaphthalene
The lower stability of 1-S is attributed to the
steric interaction between the sulfonic
group and the hydrogen atom in the
8-position.
Sulfonation