Aromaticity Reactions of Benzene

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Aromaticity Reactions of Benzene
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• For a Compound to be Aromatic
• It must have an uninterrupted cyclic cloud of p
  electrons
• - so the molecule must be a cyclic
• - every atom in the ring must have a p orbital.
• - molecule must be planar
• The p cloud must contain an odd number of pairs
  of
• p electrons

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Huckel Rule or 4n 2 Rule
An oromatic compound must have an odd number of
pairs of p electrons
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Aromatic and Nonaromatic Cyclic Hydrocarbons
Not planar
planar
planar
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Aromatic and Nonaromatic Cyclic Hydrocarbons
Not aromatic Aromatic
Not aromatic
Interrupted ring of p- orbital-bearing atoms
Have an uninterrupted ring of p- orbital-bearing
atoms
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Have an uninterrupted ring of p- orbital-bearing
atoms
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Aromatic and Nonaromatic Heterocyclic Compounds.
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A check
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A check
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Additional Examples of Heterocyclic Aromatic
Compounds
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Some Chemical Consequences of Aromaticity
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Influence of Aromaticity on Chemical Reactivity
d - 1/5 of a negative charge
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Influence of Aromaticity on Chemical Reactivity
Not Aromatic
Aromatic
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Influence of Aromaticity on Chemical Reactivity
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Which of the following compounds has a
greater dipole moment?
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Influence of Aromaticity on Chemical Reactivity
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Antiaromatic

A copmound is classified as Antiaromatic if it
fufilles the first criterion for aromaticity, but
does not fulfill the second. i.e p cloud must
contain an even number of pairs of p electrons
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A Molecular orbital Description of Aromaticity
and Antiaromaticity
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A Molecular orbital Description of Aromaticity
and Antiaromaticity
(a) benzene (b) cyclopentadienyl anion
(c) cyclopentadienyl cation (d)
cyclobutadiene
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Chemistry of Aromatic Compounds
Remember
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Now
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RXN diagram for Electrophilic Substitution
Electrophilic Addition of Benzene
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General Mechanism for Electrophilic Aromatic
Substitution Reactions
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• Five common electrophilic aromatic substitution
  reactions
• Halogenation a Br, Cl, I substitutes for
  hydrogen
• Nitration a NO2 group substitutes for hydrogen
• Sulfonation a SO3H group substitutes for
  hydrogen
• Friedel Crafts acylation a RCO group
  substitutes for
• hydrogen
• 5. Friedel Crafts alkylation a alkyl group (R)

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Halogenation of Benzene
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Halogenation of Benzene
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Halogenation of Benzene
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Halogenation of Benzene
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Halogenation of Benzene
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Halogenation of Benzene
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Nitration of Benzene
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Nitration of Benzene
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Sulfonation of Benzene
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Sulfonation of Benzene
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Principle of Microscopic Reversibility
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Principle of Microscopic Reversibility
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Principle of Microscopic Reversibility
The forward and reverse reactions must have the
same intermediates and the rate determing is the
the same in both directions
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Acylation of Benzyne
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Mechanism for Freidel-Crafts acylation
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A problem with Acylation of Benzyne
A solution use only 1 equivalent of AlCl3
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Alkylation of Benzyne
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Alkylation of Benzyne
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Alkylation of Benzyne
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Alkylation of Benzyne
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In addition Benzene can react with C generated
from alkenes
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In addition Benzene can react with C generated
from Alkenes, i.e. alkylation by alkenes
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Alkylation of benzene By Acylation Reduction
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Alkylation of benzene By Acylation Reduction
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Alkylation of benzene By Acylation Reduction
No rearrangment in acylation
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Two Methods to Reduce the carbonyl..
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Here why Two Methods to Reduce the carbonyl..
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Here why Two Methods to Reduce the carbonyl..