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
Electronicdisplacements
“Reactive Intermediates”
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. B) Reactive Intermediates
Q.-What are reactive intermediates?
Ans- Definition- “The short lived fragments or species obtained in homolytic or
heterolytic bond fission are called as reactive intermediates.”
 Ex. Carbocations, Carbanions and Free radicals.
 The organic compounds undergoes heterolytic bond fission gives carbocations
and carbanions.

4. Carbocations (Carbonium ions)
Ans-
“The positively charge carries carbon atoms containing six electrons in its
valence shell is called as carbocation or carbonium ion.”
Examples-
Q.-Explain the terms Carbocations. OR
What is carbocation? How it is formed?

5. Characteristics of Carbocations
 It is positive charge carries carbon atom.
 Six electrons in its valence shell.
 Carbocation carbon is in sp2 hybridization state.
 It is planner ion.
 It acts as electrophiles.
 It attack on electron rich species i.e. on nucleophiles.
 It is classified into primary, secondary, tertiary carbocation
 Stability order as –
tertiary > secondary > primary > Methyl carbocation
 It is product of heterolytic bond fission of organic compounds.

6. Formation of Carbocations
1. Heterolysis of Alkyl Halides-
C
H3 C
CH3
CH3
Br C
H3 C
+
CH3
CH3
Br
-
+
t - Butyl bromide t - Butyl Carbocation
2. Dehydration of Alcohols-
C
H3 CH2 OH + H
+
C
H3 CH2 OH2
+
C
H3 CH2
+
+ O
H2
ethyl alcohol ethyl carbocation

7. 3. Protonation of Alkenes-
C
H2 CH2 + H
+
C
H3 CH2
+
ethy l carbocation
Ethylene
4. Decomposition of Diazo salt-
+
C
H3 N
+
NCl
-
C
H3 N
+
N CH3
+
N2
methyl diazonium chloride Methy l carbocation

8. Stability of Carbocations
Stability of carbocation is influenced by-
A. Inductive effect-
• The electron releasing group i. e. + effect such as alkyl groups stabilize
the carbocation by dispersing the positive charge.
• Maximum number such group alkyl groups attached to positive charge
carbon greater the dispersal of positive charge and increases the stability
of carbocation.
• Thus tertiary carbocation is more stable than secondary carbocation,
which in turn is more stable than primary carbocation.

9. • -I effect due to electron withdrawing groups destabilize the carbocation.
C
H3 C
+
CH3
CH3
C
H3 CH
+
CH3 C
H3 CH2
+
CH3
+
> > >
t - butyl isopropyl ethyl methyl
Tertiary Secondary Primary Methyl
carbocation carbocation carbocation carbocation.

10. B. Resonance-
Q- Explain the stability of Allyl carbocation and n-propyl carbocation.
Ans-
• The carbocation which involved resonance are more stable than those not
involve in resonance.
• In resonance delocalization of positive charge increases the stability of
carbocation.
• Ex.- Allyl carbocation is more stable than n-propyl carbocation, because
allyl carbocation involved in resonance while n-propyl carbocation do not
involve in resonance.

11. C
H3 CH2 CH2
+
No Resonance Occur
n-Propyl carbocation-
Allyl carbocation-
Ex- Benzyl carbocation -
CH2
+
CH
+
CH2
CH
+
CH2
C
H
+
CH2
Benzyl carbocation is stabilized by resonance.
Thus, Allyl carbocation is more stable than n-propyl carbocation.

12. C. Hyperconjugation-
• Allyl group release electrons via hyperconjugation effect increases the
stability of carbocation.
• Greater the number of hyperconjugative structures the greater its stability
of carbocations.
• The decreasing order of stability of allyl carbocation as-
C
H3 C
+
CH3
CH3
C
H3 CH
+
CH3 C
H3 CH2
+
CH3
+
> > >
t - butyl isopropyl ethyl methyl

13. Recations of Carbocations
1. Combination with carbocations-
2. Elimination of Proton-
C
H3 C
CH3
CH3
OH
C
H3 C
+
CH3
CH3
O
H
-
+
t - Buty l alcohol
t - Buty l Carbocation
Nucleophile
+
C
H3 CH2
+
C
H2 CH2 H
+
Ethyl carbocation Ethylene Proton

14. 3. Addition to double bond to produce higher carbocation-
C
H3 C
CH3
CH3
CH2 C
+
CH3
C
H3
C
H3 C
+
CH3
CH3
+
t - Buty l Carbocation
C
H2
CH3
CH3
4. Rearrangement to produce more stable carbocation-
CH2 CH2
+
C
H3 CH
+
C
H3 CH3
( less stable ) ( more stable )
1 2
0 0

15. Carbanion
Ans-
“The negatively charge carries carbon atoms containing eight electrons in
its valence shell is called as carbanion.”
Examples-
Q.-Explain the terms Carbanions. OR
What is carbanion? How it is formed?
C
H3 C
-
CH3
CH3
t - Butyl Carbanion
CH3
-
Methyl carbanion
C
H3 CH2
+
ethyl carbanion
CH2
-
Benzyl carbanion

16. Characteristics of Carbanions
 It is negative charge carries carbon atom.
 Eight electrons in its valence shell.
 Carbanion carbon is in sp3 hybridization state.
 It is electron rich center.
 It acts as nucleophiles.
 It attack on electron deficient species i.e. on electrophiles.
 It is classified into primary, secondary, tertiary carbanion
 Stability order as –
Methyl > primary > secondary > tertiary carbocation
 It is product of heterolytic bond fission of organic compounds.

17. Formation of Carbanion
1. Heterolysis -
C
H3 C
CH3
CH3
Br C
H3 C
+
CH3
CH3
Br
-
+
t - Butyl bromide t - Butyl Carbocation
2. Dehydration of Alcohols-
C
H3 CH2 OH + H
+
C
H3 CH2 OH2
+
C
H3 CH2
+
+ O
H2
ethyl alcohol ethyl carbocation

18. Stability of Carbocations
Stability of carbocation is influenced by-
A. Inductive effect-
• The electron releasing group i. e. + effect such as alkyl groups stabilize
the carbocation by dispersing the positive charge.
• Maximum number such group alkyl groups attached to positive charge
carbon greater the dispersal of positive charge and increases the stability
of carbocation.
• Thus tertiary carbocation is more stable than secondary carbocation,
which in turn is more stable than primary carbocation.

19. • -I effect due to electron withdrawing groups destabilize the carbocation.
C
H3 C
+
CH3
CH3
C
H3 CH
+
CH3 C
H3 CH2
+
CH3
+
> > >
t - butyl isopropyl ethyl methyl
Tertiary Secondary Primary Methyl
carbocation carbocation carbocation carbocation.

20. B. Resonance-
Q- Explain the stability of Allyl carbocation and n-propyl carbocation.
Ans-
• The carbocation which involved resonance are more stable than those not
involve in resonance.
• In resonance delocalization of positive charge increases the stability of
carbocation.
• Ex.- Allyl carbocation is more stable than n-propyl carbocation, because
allyl carbocation involved in resonance while n-propyl carbocation do not
involve in resonance.

21. C
H3 CH2 CH2
+
No Resonance Occur
n-Propyl carbocation-
Allyl carbocation-
Ex- Benzyl carbocation -
CH2
+
CH
+
CH2
CH
+
CH2
C
H
+
CH2
Benzyl carbocation is stabilized by resonance.
Thus, Allyl carbocation is more stable than n-propyl carbocation.

22. C. Hyperconjugation-
• Alkyl group release electrons via hyperconjugation effect increases the
stability of carbocation.
• Greater the number of hyperconjugative structures the greater its stability
of carbocations.
• The decreasing order of stability of alkyl carbocation as-
C
H3 C
+
CH3
CH3
C
H3 CH
+
CH3 C
H3 CH2
+
CH3
+
> > >
t - butyl isopropyl ethyl methyl

23. 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.

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

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

26. Recations of Carbocations
1. Combination with carbocations-
2. Elimination of Proton-
C
H3 C
CH3
CH3
OH
C
H3 C
+
CH3
CH3
O
H
-
+
t - Buty l alcohol
t - Buty l Carbocation
Nucleophile
+
C
H3 CH2
+
C
H2 CH2 H
+
Ethyl carbocation Ethylene Proton

27. 3. Addition to double bond to produce higher carbocation-
C
H3 C
CH3
CH3
CH2 C
+
CH3
C
H3
C
H3 C
+
CH3
CH3
+
t - Buty l Carbocation
C
H2
CH3
CH3
4. Rearrangement to produce more stable carbocation-
CH2 CH2
+
C
H3 CH
+
C
H3 CH3
( less stable ) ( more stable )
1 2
0 0

28. Carbanion
Ans-
“The negatively charge carries carbon atoms containing eight electrons in
its valence shell is called as carbanion.”
Examples-
Q.-Explain the terms Carbanions. OR
What is carbanion? How it is formed?
C
H3 C
-
CH3
CH3
t - Butyl Carbanion
CH3
-
Methyl carbanion
C
H3 CH2
+
ethyl carbanion
CH2
-
Benzyl carbanion
B) Reactive Intermediates

29. Characteristics of Carbanions
 It is negative charge carries carbon atom.
 Eight electrons in its valence shell.
 Carbanion carbon is in sp3 hybridization state.
 It is electron rich center.
 It acts as nucleophiles.
 It attack on electron deficient species i.e. on electrophiles.
 It is classified into primary, secondary, tertiary carbanion
 Stability order as –
Methyl > primary > secondary > tertiary carbocation
 It is product of heterolytic bond fission of organic compounds.

30. Formation of Carbanion
1. Heterolysis -
2. Abstraction of Proton-
+
Na
C
H Na
+
Sodium Acetylene Acetylide Carbanion
C
-
C
H
CH2 CHO
H
+
O
H
-
+ O
H2
C
H2
-
CHO
2. Decomposition of anion-
O
-
O
C
H3 CH3
-
CO2
+

31. Stability of Carbanion
Stability of carbanion is influenced by-
A. Inductive effect-
• The electron releasing group such as alkyl groups decrease stabilize the
carbanion by intensifying the negative charge.
• The electron withdrawing group i. e. -I effect increase stabilize the
carbanion by dispersal of the negative charge.
• The stability order as –
Methyl > Primary > Secondary > Tertiary
Ex-. Methyl > Ethyl > sec-Propyl > t-Butyl

32. B. Resonance-
• Carbanions stabilized by resonance due to delocalization of the negative
charge.
• Ex.– benzyl carbocation is more stable than ethyl carbanion.
CH2
-
CH
-
CH2
CH
-
CH2
C
H
-
CH2
C
H3 CH2
-
No Resonance
Resonance structures of Benzyl carbanion

33. Reactions of Carbanion
1. Combination with proton or cation -
C
H3 CH2
-
+ H
+
C
H3 CH3
Ethyl carbanion Proton Ethane
2. Additions to multiple bonds to form an anion or new carbanion-
C
H3 C
O
H + C
H2
-
C
O
H C
H3 C
O
-
H
CH2 CH
O
Carbanion New carbanion

34. Free Radicals
Ans-
“The highly reactive odd or unpaired electron containing charge less
species is called as free radical.”
Examples-
Q.-Explain the terms Free Radicals. OR
What is Free Radical? How it is formed?
B) Reactive Intermediates

35. Characteristics of Free radical
 It is charge less species.
 It carries odd or unpaired electron in its valence shell.
 The central carbon atom of free radicals is in sp2 hybridized state.
 It is attack on free radicals and combine with free radicals.
 It has planer structure.
 It is classified into Primary, Secondary, & tertiary free radicals.
 Stability order as Tertiary > Secondary > Primary free radicals.

36. Formation of Free Radicals
1. Thermal Decomposition -
C
H3 CH2
C
H3 CH2
Pb
CH2 CH3
CH2 CH3
C
H3 CH2
4 + Pb
i
ii
Tetraethyl lead
Ethyl free radical
H5C6
O
O
O
C6H5
O H5C6 C
O
O C6H5 + CO2
Benzoyl peroxide Phenyl freeradical
Due to heating above molecule undergoes homolysis to form free radicals

37. 2. Photochemical Decomposition -
i
ii
In presence of light compound undergoes homolysis to from free radicals
Cl Cl Cl
2
homolysis
Chlorine free radical
C
H3
C
H3
O C CH2
CH3
+ CH3
Acetyl free radical
methyl free radical
Acetadehyde

38. Stability of Free Radicals
1. Resonance-
• According to resonance theory those molecule gives maximum resonating
structures which are more stable.
• Free radicals get stability by resonance due to delocalization of the
unpaired electron.
• Ex. Allyl free radicals–
Benzyl free radical-
C
H2 CH CH2 C
H2 CH CH2
I II
CH2
CH
CH2
CH
CH2
C
H
CH2
I II III IV
Resonance structures of benzyl free radicals
In above two examples benzyl free radicals more stable than allyl free radicals.

39. 2. Hyperconjugation Effect-
• The alkyl groups are electron releasing groups.
• The presence of alkyl group attached to free radical carbon increases the
stability of free radical.
• Hence the decreasing order of stability of free radical is
• Presence of alkyl group increases the hyperconjugation
structures.

40. Reactions of Free Radicals
1. Combination with other free radicals-
2. Addition to multiple bond to form a new free radicals-
3. Disproportionation-

41. 4. Substitution-