Electrophilic Aromatic Substitution

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Electrophilic Aromatic Substitution
Electrophilic Aromatic Substitution involves the
attack on the electrophile by the ? electrons of
the aromatic ring and replacing one of the
hydrogen molecules on the ring. In this Learning
object, this reaction has been analysed by
understanding the changes that occur in the
molecular orbitals of the reactants.
Author Sukumar Honkote Chemistry
Department, IIT Bombay
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Learning objectives

• After interacting with this learning object, the
  user will be able to
• Explain the process of electrophilic aromatic
  substitution

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Definitions
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• Electrophile is a reagent that participates in a
  chemical reaction by accepting an electron pair
  in order to bond to a nucleophile.
• 2. Nucleophile is a reagent that forms a
  chemical bond to its reaction partner (the
  electrolyte) by donating both bonding electrons.
• 3. Molecular Orbital is a mathematical function
  that
• describes the wave-like behavior of an
  electron in a
• molecule.
• 4. ? Orbital The molecular orbital of the ?
  bond. It is
• the shape of the maximum probability function
  of the ?
• electrons.

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Concept
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1) Aromatic compounds like benzene undergo
electrophilic aromatic substitution
reactions. 2) Electrons in a molecule do not
remain stationary but move about the
molecule in defined volumes. The shape of these
volumes are given by molecular orbitals. The
probability of finding electrons in these
volumes is maximum. 3) The ? bond (double bond)
is electron rich while an electrophile is
electron poor. 4) In the reaction the electron
rich ? bond is attracted towards the
electrophile E and vice versa. Due to this
attraction the shape of the orbitals
(volumes) change and bend towards each other.
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Concept
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5) Thus the ? bond breaks and a new bond between
C E is formed. The E-A bond also gets
broken. 6) Now a positive charge is created on
the adjacent carbon also the benzene became
unstable. Thus the electrons from the C-H
bond reform the ? bond and the C-H bond breaks to
form a proton (electronless hydrogen) which
leaves. Now the stability of the benzene is
regained. 7) In benzene, the hydrogen is
replaced and electrophile E comes there.
Hence its a substitution reaction.
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Credits
Play/pause
Restart
What will you learn
Reaction Mechanism
Reaction at Orbital level
Lets Learn!
Interactivity options Sliders(IO1)? / Input
Boxes(IO2)? /Drop down(IO3)? (if any)?
Definitions
Concepts
Test your understanding (questionnaire)?
Animation Area
Lets Sum up (summary)?
Want to know more (Further Reading)?
Output result of interactivity (if any)?
Instructions/ Working area
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REACTION MECHANISM
Note The animation will begin with Reaction
Mechanism (default)?
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REACTION MECHANISM
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REACTION MECHANISM
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REACTION MECHANISM
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REACTION MECHANISM
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REACTION MECHANISM
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REACTION MECHANISM
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REACTION MECHANISM
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REACTION MECHANISM
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REACTION MECHANISM
The reaction mechanism animation ends here. The
next slide onwards are animation details for
reaction at orbital level.
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Summary

• Electrophilic aromatic substitution or EAS is
  an organic reaction in
• which an atom, usually hydrogen, appended to
  an aromatic system is
• replaced by an electrophile.
• It involves the attack on the electrophile by the
  ? electrons of the aromatic ring and replacing
  one of the hydrogen molecules on the ring.
• There are three fundamental components to an
  electrophilic aromatic substitution mechanism
• formation of the new s bond from a CC in the
  arene nucleophile
• removal of the proton by breaking the C-H s bond
• reforming the CC to restore the aromaticity

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Links for further reading
Books a) Fundamentals of Organic Chemistry by
Solomon and Graham b) Organic Chemistry by
Clayden, Greevs, Warren and W others
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Questionnaire
To be given by Prof Anindya Datta