Chapter 8: ARENES potx

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ORGANIC CHEMISTRY
Dr Nam T. S. Phan
Faculty of Chemical Engineering
HCMC University of Technology
Office: room 211, B2 Building
Phone: 8647256 ext. 5681
Email:
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Chapter 8: ARENES
Benzene
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CRITERIA FOR AROMATICITY
To be classified as aromatic, a compound must
meet both of the following criteria:
•
It must have an un-interrupted cyclic
π
cloud
above & below the plane of the molecule
•
The π cloud must contain (4n + 2)
π
electrons (n
= 0, 1, 2…)
un-interrupted
cyclic
π
cloud
6 π e = 4 x 1 + 2
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Aromatic:
(-)
(+)
(+)
N
H
O S
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NOT aromatic:
(+)
(.)
(.)
(-)
4 π e 5 π e
7 π e
8 π e
NOT (4n + 2)
π
e
Interrupted
cyclic
π

cloud
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NOMENCLATURE OF
MONOSUBSTITUTED BENZENES
Name of substituent + benzene
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Names have to be memorized:

8
NOMENCLATURE OF DI- &
POLYSUBSTITUTED BENZENES
Alphabetical order, 1-position for the 1
st
stated substituent
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1 of the substituents can be incorporated into a name:
Names
incorporating
2 substituents
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Alphabetical
order
Lowest possible
numbers
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PREPARATION OF BENZENE
Petroleum Bezene
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REACTIONS OF BENZENE
Halogenations of benzene
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Reaction mechanism: electrophilic substitution
Catalyst regeneration
14
Nitration of benzene
15
Sulfonation of benzene
Reversible reaction

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Reaction mechanism: electrophilic substitution
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Friedel-Crafts Alkylations of benzene
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19
Carbocation
rearrangement
20
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Friedel-Crafts Acylations of benzene
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Reaction mechanism: electrophilic substitution
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Rearrangement
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REACTIONS OF SUBSTITUTED
BENZENES
Relative rates of electrophilic substitutions:
Electron-
donating
Electron-
withdrawing
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Relative reactivity
Electron-donating Eelectron-withdrawing
Activating Deactivating
ortho/para-directing meta-direcring
+I,
+C,

+H
- I,
-C,