electronic effects

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Organic ChemistryElectronic EffectsAs per the
New CBCS Syllabus

• Lecture -1

By Sri. VEERESH HALEMANE M.Sc. K.SLET.
(Ph.D.) Government First Grade College Humnabad
.
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Syllabus for Semester - I

• 1. Atomic Structure
• 2. Chemical Periodicity
• 3. Chemical Bonding Molecular structure
• 4. Fundamentals of organic chemistry
• 5. Stereochemistry
• 6. Aliphatic Hydrocarbons

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Electronic effects
The electronic effects operating in organic
molecules are
1. Inductive Effect
2. Resonance or Mesomeric effect
3. Electromeric effect
4. Hyperconjugation
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What is inductive effect ( I effect)?
Permanent displacement of sigma electrons along a
saturated carbon chain when some atoms or group
of atoms with different electronegativity other
than carbon is attached to carbon chain is called
Inductive effect
It is a permanent effect
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Types of Inductive effect
Inductive effect is of two types
Positive Inductive effect ( I effect)
Negative Inductive effect ( I effect)
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What is positive inductive effect?
It is the permanent displacement of sigma
electrons along the carbon chain due to the
attachment of less electronegative atom or group
to the carbon chain.
It results in partial negative charge on carbon
atoms and partial positive charge on the group.
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What is Negative inductive effect?
It is the permanent displacement of sigma
electrons along the carbon chain due to the
attachment of more electronegative atom or group
to the carbon chain.
It results in partial positive charge on carbon
atoms and partial negative charge on the group.
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Examples for () I groups and ( -) I groups
Ex of I groups ter .alkylgtsec .alkylgtprimary
alkylgt -C H 3 gt-H
Ex of I groups ?? ?? 3 gt?? ?? 2 gt????gt?? ?? 3
??gt????Ogt????gt????????gt??????lgt ????????gt??????
?? 2 gt??gt????gt??rgt??gt????gt????gt?? ?? 2 gt ?? 6 ??
5 gt??
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What is Electromeric effect (E - effect)?
The complete displacement of p-electrons towards
the one of the bonded atoms in presence of an
attacking reagent is called electromeric effect.
It is a temporary effect.
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Types of Electromeric effect (E)
There are two types of electromeric effect
1. Positive electromeric effect ( E effect)
2. Negative electromeric effect ( E effect)
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What is negative electromeric effect ?
When the transfer of electrons takes place away
from the attacking reagent. It is called E
effect.
It is found during nucleophillic attack on
organic molecules.
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What is positive electromeric effect?
When the transfer of electrons takes place
towards the attacking reagents is called E
effect
It is found during electrophilic attack on
organic molecules.
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What is Resonance or Mesomerism?
The phenomenon in which a molecule is represented
by more than one Lewis structure differing only
with respect to position of electrons is known as
resonance.
The various structures are known as Resonating or
contributing or cannonical structures.
The actual molecule is the hybrid of all these
structures known as resonance hybrid.
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What is the criteria for resonance?
The molecule should possess a conjugated system
to exhibit resonance.
Example Benzene molecule shows resonance due to
the presence of cyclic conjugation.
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Types of conjugated systems

• p p conjugation
• ex

(2) Positive charge p conjugation ex
(3) Negative charge p conjugation ex
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Types of conjugated systems
(4) Odd electron p conjugation ex
(5) Lone pair p conjugation ex
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Rules to write resonance structures
All resonating structure must have the same
arrangement of atomic nuclei
All resonating structure should have same number
of unpaired electrons.
The contributing structures should have nearly
same energy
All atoms which are the part of Delocalization
must be in a same plane.
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Rules to find the most contributing structures
A structure with most number of covalent bonds is
more stable and more contributing.
Structure (I) is more stable than structure (II)
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Rules to find the most contributing structures
A non polar structure is more stable than a polar
structure
Structure (I) is more stable than structure (II)
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Rules to find the most contributing structures
Structures having complete octet is more stable
than the structures having incomplete octet.
Structure (II) is more stable than structure (I)
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Rules to find the most contributing structures
Among polar structures, the structure with
negative charge on more electronegative atom and
positive charge on less electronegative atom is
more stable
Structure (II) is more stable than structure (I)
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Rules to find the most contributing structures
The energies if the different resonating
structures must be the same (or) nearly the same.
All atoms that are part of the resonance must be
in a same plane. Ex Out of three lone pair on
chlorine only one which is same plane to ? bond
are involved in the resonance.
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Rules to find the most contributing structures
Increase in charge separation decreases the
stability of a resonance structure. Ex Stabili
ty ??gt????gt????
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Resonance
In Pyridine out of lone pair and ?
electrons on Nitrogen which are involved in
Delocalization process? and why?
Ans ? - Electrons are involved in resonance
because lone pair are present in sp2 hybrid
orbital which are in different plain