CONTEXT:
Electron displacement mechanism,inductive effect(+I,-I),electromeric effect(+E,-E),resonance(Resonance hybrid),hyper conjugation(stability of carbocation,freeradical and alkene)
There are FOUR type of elctron displacement mechanism observer in organic chemistry.
1)Inductive effect(permanent effect)
2)Electromeric effect(Temporary effect)
3)Resonance effect(mesomeric effect)(Permanent effect)
4)Hyperconjugation(Permanent effect)
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1) INDUCTIVE EFFECT:
It is a permanent effect,in which electron pair in carbon chain are flow towards more electronegative(EN) group.It is denoted by Ieffect.Inductive effect is of 2 types on the basic of electronegativity(EN).
First one is +Ieffect and another is -I effect.
a) -I effect:
When a group with greater electronegativity as compared to hydrogen bonded with carbon chain,withdraw electron from carbon chain towards itself.Using this mechanism we can also know about the stability of atom,more acidic element etc.so the electronegativity is given below in the decreasing order.
The above groups are in their decresing order of electronegativity(EN).Acoording to those functional froup the acidic nature and stability can be determine.for example firts we consider the
acidic nature:
Let's take H-COOH and CH3-COOH.which is more acidic?let's know.
H-COOH=(H-Coo-)+(H+)Electronegativity of H is consider as 0(zero).
CH3-COOH=(CH3-COO-)+(H+)Electronegativity of CH3>H,so the negative charge on CH3-COO- increses and the acidic nature decreases as the -ve ion is unstable.
ACIDIC NATURE:
HA=(H+)+(A-),acidic nature depends on the stability of A- ion.so H-COOH is more acidic then CH3-COOH.
Then ,comes to +I effect.
b) +I effect:
When a lesser electronegative group as compared to H atom bonded with carbon chain,it donates electron to the carbon chain.let's know the functional group in their decreasing order.
2) ELECTROMERIC EFFECT:
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3) RESONANCE:
In the above two(I,II) diagram,electronic structure of Benzene is shown.But none of the structure is actually constant with known property of Benzene.
The phenomenon in which,there is more then one structure for the compound but none of them actually able to explain it's property ,is known as Resonance and the the different structure are known as Resonating structure.The actual structure of a compound is known as Resonance Hybrid.It is also known as Mesomeric effect.
The flow of electron from one part to another in a π-system,caused by resonance is called Mesomeric (Resonance)effect.
It is also of 2 types.
1)+M effect
2)-M effect
a)+M effect:
Same as inductive effect,in this category ,if a group donates electron to π-system ,then it has +M effect.Group showing +M effect are:
Functional group:EXAMPLE-1: In this example,the dot around chlorine atom(.)Represents the valence electron.
Valence electron of
Cl atom is
7.But cl atom is bonded eith
CH2=CH and another six bond are represented as
Dot(.)EXAMPLE-2:Here,
Triple bond converts to
Double bond,while a
-ve charge is free and
NH2 turns into
NH2+.The
Valence electron of
N is
5.At firts it bonded with
two H atom and another with the
Benzene ring.so there is
Two electron remains as
Valence electron,and the
Valence electron is represented by the
Dot(.) In the left side of
N atom.
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VALENCE ELECTRON:
The electron in the outermost shell of an atom,is known as valence electron.
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b)-M effect:
Functional group withdrawing elctron towards themself using resonance ,are showing -M effect.
Functional group:
It is also known as No-Bond Resonance.it only takes place in sigma bond.It has mainly 3 properties,given below.
1)Stability of carbocation
2)Stability of freeradical
3)stability of alkene
1)Stability of carbocation:
Stability of carbocation is also known as Sigma-P orbital resonance.Because electron(e-)in Sigma bond moves towards P orbital of H atom.
EXPANDED FORM:
As you see in the above pic that
electron are moves towards
P-orbital of
H atom from
Sigma bond,it is known as
Sigma-P orbital Resonance.
2)Stability of free radical :
When Overlap between a Sigma bond of alkyl group and a P-orbital containing odd number of electron occur,the overlap result in binding Two carbons and One H atom to some extent.Stability of freeradical is in the order:
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[ Tertiary>secondary>primary>CH3 ]
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3)Stability of Alkene:
NOTE:
More the number of alpha H(H atom bonded to carbon chain) atom next to carbon chain more is the stability of alkene.
CH3-CH2,here the hydrogen atom present before -CH2 group is known as alpha H atom.
The carbon atom next to the CH2 group is known as alpha carbon.
CH2-C,here the carbon atom next to CH2- group is known as alpha carbon atom
Stability of some alkene are given below in the number of their alpha H atom.more the number of alpha H atom more the stability.
In the diagram
(a) number of
alpha H atom is
12.In the second diagram
(b) number of
alpha H atom is
9,and in the last diagram
(c) number of
alpha H atom is
6.we know the
alkene with higher
alpha H atom is more stable.so the stability is in the
order: a>b>c
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SUMMARY:
By using Electron displacement mechanish we can establish the stabily of atom,we can study the electron movement from one to another bond ,to establish which is the pure acid and to establish the mechanism of electron movement.
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