Chemistry B.Sc.-I Sem-Ist Sant Gadge Baba Amravati University, Amravati, Late Ku. Durga K. Banmeru Science College, Lonar

1. 1
Late Ku. Durga K. Banmeru Science College,
LONAR DIST. BULDANA (Maharashtra), India.
Section –II
Unit-3
Electronic displacements
Dr. Suryakant B. Borul
Head Of Department
Department of Chemistry
Late Ku. Durga K. Banmeru Science College, Lonar
B. Sc. Ist year Sem-Ist Subject:- Chemistry

2. 2
Dr. Suryakant B. Borul
(M.Sc., M.Phil., Ph.D.)
Head Of Department
Department of Chemistry
Late Ku. Durga K. Banmeru Science College,
Lonar
Teacher Profile

3. Introduction-
Organic compounds containing covalent bond and electron displacements
take place in covalent bonds, due to this organic compounds shows different
behavior.
These electronic displacements in a molecule may be due to certain
effects, some of which are permanent and other are temporary .
Unit -3- Electronic Displacements
Electronic Displacements
Permanent effects Temporary effects
1. Inductive 1. Electromeric effect
2. Resonance

4. 1. Inductive Effect-
Q. Explain the term Inductive effect.
Ans- “The permanent polarization develop in single covalent bond due displacement
of sigma electrons towards more electronegative atom is called as inductive effect.”
Example-
Consider in carbon chlorine bond, chlorine atom is more electronegative, hence sigma
electron pair move towards chlorine and it acquire negative charge while carbon acquire
positive charge.

5. Important point-
 It is permanent polarization/ effect.
 It is developed in sigma covalent bond
 In this effect sigma electron move towards more electronegative atom.
Bonded atoms acquires partial positive and negative charge.
In this effect there is no need of reagent.
 It is denoted by placed arrow head in the middle of the bond pointed towards more
electronegative atom

6. Types of Inductive Effect
There are two types of inductive effect.
1. Positive Inductive effect (+I effect)-
2. Negative Inductive effect (-I effect)-
1. Positive Inductive effect (+I effect)-
The inductive effect due to electron releasing group such inductive effect is called as
Positive Inductive effect (+I effect).
Ex-
Positive Inductive effect

7. 2. Negative effect (+I effect)-
The inductive effect due to electron withdrawing group such inductive effect is called
as Negative Inductive effect (-I effect).
Ex-
Negative Inductive effect
Inductive effect is transmitted along a chain of carbon atoms

8. Application of Inductive Effect
1. Relative strength of Chloroacetic acid and acetic acid-
2. Relative strength of Formic acid and acetic acid-
3. Relative strength of Methyl amine and ammonia-

9. 1. Relative strength of Chloroacetic acid and acetic acid-
Q.- Explain relative strength of Chloroacetic acid and acetic acid
The inductive effect due to electron withdrawing group such inductive effect is called as
Negative Inductive effect (-I effect).
Ex-

12. 1. Relative strength of Chloroacetic acid and acetic acid-
Q.- Explain relative strength of Chloroacetic acid & acetic acid
 The of acid depends on the tendency to reduce H+ ion.
 Greater the tendency to release H+ ion greater strength of an acid.
 The strength of acid is expressed in terms of pKa value.
 Lesser the pKa value greater the strength of an acid.

13. In chloroacetic acid due to presence of chlorine electron withdrawing group –I
effect develop in O-H bond of carboxylic group hence release H+ ion easily and
increase the strength of acid thus pKa value is 2.86.
While in case of acetic acid alkyl group acts as electron releasing group hence pKa
value is 4.76 i.e. H+ ion not remove easily (+I effect).
Thus chloroacetic acid is strong acid than acetic acid.

15. 2. Relative strength of Formic acid and acetic acid-
Q.- Explain relative strength of Formic acid & acetic acid
 The strength of acid depends on tendency to release H+ ion. In case of
carboxylic acid H+ releasing strength increases due to electron withdrawing
group or atom attached carboxylic carbon or adjacent carbon.
 In acetic acid, the electron releasing methyl group opposes the release of proton as
compare to formic acid .
i.e. +I effect develop in acetic acid while in formic acid such effect not develop.
Hence formic acid stronger than acetic acid.

16. 3. Relative strength of methyl amine and ammonia-
Q.- Explain relative strength of methyl amine & ammonia.
 The strength of base containing Nitrogen, depends on the availability of nitrogen
lone pair electron for protonation.
More basic Less basic

17. In case of methyl amine, methyl group acts as electron releasing group hence lone
pair on nitrogen easily available for protonation.
 While in ammonia no such electron releasing group or atom attached to nitrogen.
Thus due to +I effect in CH3-NH2 molecule methyl amine is more basic than that
of NH3.

18. Q- What is electromeric effect?
Unit -3- Electronic Displacements
Electromeric Effect
Ans- Definition- The complete temporary transfer of pi electron pair towards one of
the bonded atom under the influence of reagent is called as electromeric
effect or E -effect.
General Example-

19.  IMP points /Characteristics of Electromeric effect-
 It is temporary effect.
 It is occur in multiple bond compounds
 This effect under influence of reagent
 Pi electrons pair involved in this effect.
 Bonded atoms acquires complete positive and negative charges.
 It is denoted by curve arrow ( ) pointed towards electron transfer atom.

20. 1. Positive Electromeric effect (+E effect)-
2. Negative Electromeric effect (-E effect)-
Types of Electromeric effect
1. Positive Electromeric effect-
Ans- The electromeric effect in which pi electron pair transfer towards attacking
reagent (electrophile) is called as Positive Electromeric effect or + E effect.

21. 2. Negative Electromeric effect-
Ans- The electromeric effect in which pi electron pair transfer away from attacking
reagent (nucleophile) is called as Negative Electromeric effect or -E effect.

22.  Application of Electromeric effect
There are number of reactions which involve E-effect.
 1. Electrophilic addition reaction of alkenes & alkynes.
2. Nucleophilic addition reaction of Carbonyl compounds.
3. Electrophilic Substitution reactions of aromatic compounds.

23. Resonance or Mesomeric Effect
Q.-Explain or write a note on Resonance or mesomeric effect
Ans- Definition- The process in which two or more valence bond structures can be
written for a molecule in order to explain all it’s properties is called as
Resonance effect (R-effect) or mesomeric effect (M-effect). OR
The process in which interaction between two conjugated - bonds
or - bond and lone pair of electrons is called as resonance effect or
mesomeric effect.
Resonance Structure of Benzene

24.  IMP points /Characteristics of Electromeric effect-
 This effect involved interaction between two conjugated - bonds or - bond
and lone pair of electrons.
 This molecules must contain - bonds.
 This effect explain the stability of molecule.
 Greater the resonance structures greater the stability of molecules.
 A double headed arrow ( ) is used for resonance structure. It is permanent
effects.
 It is also called as mesomeric effect.

25. Example-
1. Positive Resonance effect (+R effect) or Mesomeric effect (+M
effect)-
2. Negative Resonance effect (-R effect) or Mesomeric effect (-M
effect)-
Types of Resonance effect

26. 1. Positive Resonance effect (+R effect) or Mesomeric effect (+M
effect)-
The resonance effect in which atoms or group which release electron
towards carbon atom are called as positive resonance effect (+ R-effect) or
positive mesomeric effect (+M-effect).
Electron releasing atom or group as:-Cl, -Br, -I, -OH, -OR, -NH2
Here interaction in between pi electron and lone pair of electrons

27. 2. Negative Resonance effect (-R effect) or Mesomeric effect (-M
effect)-
The resonance effect in which atoms or group which withdraw electron
away from carbon atom are called as negative resonance effect (- R-effect) or
negative mesomeric effect (-M-effect).
Electron releasing atom or group as:-COOH, -NO2, -CN, -C=O, -CHO, -
COOR etc.
Here interaction in between pi electrons

28. Application of Resonance effect
Resonance effect is useful to explain
Stabilities of molecules and ions
Unexpected bond length in molecule and ions
Acidity of Phenols and basicity of amines
Explains the mechanism of reactions

29. Hyperconjugation or Hyperconjegative Effect
Ans- Definition- The delocalization or conjugation of sigma bond electrons with pi
bond electrons is called as hyperconjugation or hyperconjugative effect.
Ex-
Q.-Explain or write a note on Hyperconjugation effect

30. Characteristics of Hyperconjugative effect
In this effect interaction between sigma and pi bond electrons
For this effect carbon hydrogen sigma bond at alpha position to the double bond
is must.
In 1935 Nathan and Baker proposed this effect.
It is a permanent effect.
It explain the stability of molecules hyperconjuagtion structure increase stability
increases.

31. Application of Hyperconjugation effect
It is used to explain relative stabilities of alkenes.
 It is used to explain relative stabilities of carbocations.
It is used to explain relative stabilities of free radicals.
Greater the hyperconjugation in structures greater the stability of molecules or
ion.

32. 1. Relative Stabilities of Alkenes
Ans-
1. The molecules or alkenes which gives maximum structure of hyperconjugation
which are more stable.
2. Ethene or ethylene does not gives any hyperconjugative structure.
3. While propene gives three hyperconjugative structures.
Thus propene is more stable than ethene
Q.-Explain propene is more stable than ethene on the basis of
hyperconjugation.

34. 2. Relative Stabilities of Carbocations
Ans-
1. The tertiary carbocation is more stable than secondary carbocation and
secondary carbocation more stable than primary carbocation.
2. The stability order as –
Tertiary > Secondary > Primary > Methyl
Ex-. t-Butyl > sec-Propyl > Ethyl > Methyl
3. The carbocations which gives maximum structure of hyperconjugation which
are more stable.
Q.-Explain tertiary carbocation is more stable than primary carbocation.

35. t-butyl carbocation gives nine hyperconjugative structures
sec-propyl carbocation gives six hyperconjugative structures
4.
5.

36. 6.
ethyl carbocation gives three hyperconjugative structures
Thus t-carbocation is more stable than primary carbocation.

37. 3. Relative Stabilities of Free radicals
Ans-
According to hyperconjugative effect those species gives maximum
hyperconjugative structures which is more stable.
 The tertiary free radicals gives more hyperconjugative structures than secondary
free radicals and secondary free radicals gives more hyperconjugative structures
than primary free radicals.
 The primary free radicals is more stable than methyl free radical.
 The stability order as –
Tertiary > Secondary > Primary > Methyl
Ex-. t-Butyl > sec-Propyl > Ethyl > Methyl
Q.-Explain the relative stability of free radicals.

38. Hyperconjugative
structures No. 09 06 03 zero