This document discusses different electronic effects in organic chemistry. It describes inductive effect as a permanent polarization of electron density between two unlike atoms in a bond. Electron-withdrawing and electron-releasing groups are discussed. Mesomeric effect allows for resonance stabilization through delocalization of charge in conjugated systems. Electromeric effect involves the temporary shift of a pi bond electron pair to one atom upon reaction with an electrophile. The order of effects from strongest to weakest is given as mesomeric, electromeric, and inductive. Applications to stability of ions and carbocations are outlined.

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2. ELECTRONIC EFFECTS
INDUCTIVE EFFECT ,
MESOMERIC EFFECT
ELECTROMERIC EFFECTS
BY
-Neha Tripathee
Assistant Professor
K.M.G.G.P.G.COLLEGE BADALPUR
B.Sc.I .PAPER II,UNIT II

3. Inductive Effect
 The inductive effect is a permanent
state of polarization. The electron
density in a bond between two unlike
atoms is not uniform.
 The inductive effect is a distance-
dependent phenomenon
 The inductive effect is permanent, but
relatively weak, and can be easily
overshadowed by the electronic
effects discussed later.

4.  There are two categories of inductive effects:
the electron-withdrawing (-I effect) and
the electron-releasing (+I effect).
 –NH3
+ > –NO2 > –SO2R > –CN > –SO3H > –
CHO > –CO > –COOH > –COCl> –CONH2 >
–F > –Cl > –Br > –I > –OH > -OR > -NR2 > –
NH2 > –C6H5 > –CH=CH2 > –H
 The strength of inductive effect is also
dependent on the distance between the
substituent group and the main group that
react; the greater the distance, the weaker
the effect.

5. Applications-
 The inductive effect is used to tell the stability of the ion.
 STABILITY OF ION α 1/CHARGE DENSITY
 The inductive effect can be used to determine the stability of a
molecule depending on the charge present on the atom and the
groups bonded to the atom. For example
 if an atom has a negative charge and is attached to
a +Igroup its charge becomes 'amplified' and the
molecule becomes more unstable.

6. CONT….
 If an atom has a negative charge and
is attached to a -I group its charge
becomes 'de-amplified' and the
molecule becomes more stable than if
I-effect was not taken into
consideration.
 STABILITY OF CARBOCATION-
 tertiary carbocation > secondary
carbocation >primary carbocation >
methyl carbocation

7. STRENGTH OF CARBOXYLIC ACID
 It depends on the extent of its
ionisation, The more ionized is it, the
stronger it is.
 As an acid becomes stronger, the
numerical value of its pKa drops.
 Thus Acetic acid < formic acid <
chloro aceic acid
 And mono chloro acetic acid<dichloro
acetic acid<tri chloro acetic acid

8. Comparison between inductive
effect and electromeric effect
Inductive Effect Electromeric Effect
 The polarization of a
single σ covalent bond
due to the
electronegativity
difference between the
bonding atoms is called
the inductive effect
 It is a permanent effect
 It doesn't need the
presence of a reagent
 Induced charges appear
as partial charges(∆+
or∆−)
 The complete shift of the π
bond electron pair of a
double or triple bond to one
of the atoms joined by it, in
the presence of a suitable
electrophilic reagent, is
called the electromeric
effect
 It is a temporary effect
 It needs the presence of an
electrophilic reagent
 Induced charges are
integral: +1 or −1

9. ELECTROMERIC EFFECT-
 This effect is shown by those
compounds containing multiple bonds.
When a double bond or triple bond is
exposed to an attack by a reagent, a pair
of bonding electrons involved in the pi
bond is transferred completely from one
atom to another. This effect will remain
as long as the attacking reagent is
present. As soon as the reagent is
removed, the polarized molecule will
come back to the original state.

10. +E and -E groups
 Electromeric effect can be classified into
+E and -E effects based on the direction
of transfer of the electron pair.
 When the electron pair moves towards
the attacking reagent, it is termed as the
+E effect. The addition of acids on
alkene is an example of the +E effect.
 The -E effect can be found in reactions
such as addition of nucleophiles to
carbonyl compounds.

11. MESOMERIC EFFECT-
 The concepts of mesomeric effect,
mesomerism and mesomer were introduced
by Ingold in 1938 as an alternative to
Pauling's synonymous concept of
resonance.[1] "Mesomerism" in this context is
often encountered in German and French
literature, but in English literature the term
"resonance" dominates.
 Mesomeric effect can be transmitted along
any number of carbon atoms in a conjugated
system. This accounts for the resonance
stabilization of the molecule due to
delocalization of charge.

12. EFFECT ORDER :
 +M
 –O− > –NH2 > –NHR > –OR > –
NHCOR > –OCOR > –Ph > –F > –Cl
> –Br > –I
 -M
 –NO2 > –CN > --HSO3 > –CHO > –
C=O > –COOCOR > –COOR > –
COOH > –CONH2 > –COO−


13.  MESOMERIC EFFECT IS A
PERMANENT EFFECT AS THE
INDUCTIVE EFFECT.
 IT OPERATES IN COMPOUNDS
WHERE THER IS CONJUGATION
,I.e. PAI BOND AND SIGMA BOND
BOTH ARE THERE.
 IT IS RESPONSIBLE FOR MORE
THAN ONE RESONANCE HYBRID
STRUCTURES OR MESOMERIC
FORMS OF THE COMPOUND.