Reaction Intermediates: Complete Overview | Chemistry Optional Notes for UPSC PDF Download

 Page 1


Reaction Intermediates.  
Short lived fragments called reaction intermediates result from homolytic and Heterolytic bond 
fission. The important reaction intermediates are free radicals, carbocations, carbonions, 
carbenes, benzyne and nitrenes. 
 
Free radicals 
A free radical may be defined as an atom or group of atoms having an odd or unpaired electron. 
These result on account of homolytic fission of a covalent bond and are denoted by putting a dot 
(.) against the symbol of atom or group of atoms. 
 ;
.
;
.
;
.
radical free
Methyl    
3
radical free
Hydrogen
radical free
Chlorine
C H H C l
r adi c al f r e e
E t hy l
H
H
C C H
. |
|
3
? ;        
radical
methyl Triphenyl
5 6
5 6
5 6
. |
|
H C
H C
C H C ? 
The first stable organic free radical was triphenyl methyl radical and it was prepared by 
Gomberg. 
 
(1) Characteristics of free radical. 
(i) The formation of free radical is initiated by heat, light or catalysts. 
(a) 
. .
:
sunlight
Energy
l C l C C l C l ? ? ? ? ? ?   
   
(b) 
. .
:
3
102
3
H C H H C H
k c al
? ? ? ? ? ? 
 
(c) 
(primary)
2 3
97
2 3
. .
H H C C H H C H C H
k c al
? ? ? ? ? ? ? ? ?   
 
(d)
) (secondary
3
3
94
3
3
. .
H H C
C H
C H
H C H
C H
C H
k c al
? ? ? ? ? ? ? 
 
 
Page 2


Reaction Intermediates.  
Short lived fragments called reaction intermediates result from homolytic and Heterolytic bond 
fission. The important reaction intermediates are free radicals, carbocations, carbonions, 
carbenes, benzyne and nitrenes. 
 
Free radicals 
A free radical may be defined as an atom or group of atoms having an odd or unpaired electron. 
These result on account of homolytic fission of a covalent bond and are denoted by putting a dot 
(.) against the symbol of atom or group of atoms. 
 ;
.
;
.
;
.
radical free
Methyl    
3
radical free
Hydrogen
radical free
Chlorine
C H H C l
r adi c al f r e e
E t hy l
H
H
C C H
. |
|
3
? ;        
radical
methyl Triphenyl
5 6
5 6
5 6
. |
|
H C
H C
C H C ? 
The first stable organic free radical was triphenyl methyl radical and it was prepared by 
Gomberg. 
 
(1) Characteristics of free radical. 
(i) The formation of free radical is initiated by heat, light or catalysts. 
(a) 
. .
:
sunlight
Energy
l C l C C l C l ? ? ? ? ? ?   
   
(b) 
. .
:
3
102
3
H C H H C H
k c al
? ? ? ? ? ? 
 
(c) 
(primary)
2 3
97
2 3
. .
H H C C H H C H C H
k c al
? ? ? ? ? ? ? ? ?   
 
(d)
) (secondary
3
3
94
3
3
. .
H H C
C H
C H
H C H
C H
C H
k c al
? ? ? ? ? ? ? 
 
 
(e) 
(tertiary)
3
3
3
91
3
3
3
. .
H C
C H
C H
C H
H C
C H
C H
C H
k c al
? ? ? ? ? ? ? 
 
(f) 
(allyl)
2 2
86
2 2
. .
H H C C H C H H C H C H C H
k c al
? ? ? ? ? ? ? ? ? ? ? 
 
(g)   ? ? ? ? ? ? ?
k c al
H C H
88
2
(benzyl)
2
. .
H H C ? ?  (h) 
2 3
/
2 3
. .
H N H C N H C H
l i ght h e at
? ? ? ? ? ? ? ? 
 
(ii) Free radicals are generally electrically neutral. 
 
(iii) There are seven electrons in the out most orbit of carbon of carbon free radicals. 
 
(iv) Owing to the presence of an odd electron; a carbon radical is paramagnetic in nature. Due to 
this reason free radicals are highly reactive. 
 
(v) Free radicals are neutral electrophiles. 
 
(vi) Chemical reactions which takes place with the formation of free radical as an intermediate 
are known as free radical reactions. These reactions takes place in three steps, 
 (a) Initiation  
 (b) Propagation and   
 (c) Termination 
 
Each of these steps, in turn, may involve two or more steps. 
(a) Initiation step: In this step, homolytic bond fission takes place in the presence of 
initiator, i.e., peroxide, h v , heat etc. The process is always endothermic. 
   l C l C C l C l
o r h v
. .
? ? ? ? ? ?
?
v e H ? ? ? 
(b) Propagation step: Propagation step is always two or more than two step process and 
all propagation steps should be exothermic, otherwise free radical reactions would 
not take place. 
Propagation step I: In this step, formation of free radical as reaction intermediate takes 
place. For example, 
Page 3


Reaction Intermediates.  
Short lived fragments called reaction intermediates result from homolytic and Heterolytic bond 
fission. The important reaction intermediates are free radicals, carbocations, carbonions, 
carbenes, benzyne and nitrenes. 
 
Free radicals 
A free radical may be defined as an atom or group of atoms having an odd or unpaired electron. 
These result on account of homolytic fission of a covalent bond and are denoted by putting a dot 
(.) against the symbol of atom or group of atoms. 
 ;
.
;
.
;
.
radical free
Methyl    
3
radical free
Hydrogen
radical free
Chlorine
C H H C l
r adi c al f r e e
E t hy l
H
H
C C H
. |
|
3
? ;        
radical
methyl Triphenyl
5 6
5 6
5 6
. |
|
H C
H C
C H C ? 
The first stable organic free radical was triphenyl methyl radical and it was prepared by 
Gomberg. 
 
(1) Characteristics of free radical. 
(i) The formation of free radical is initiated by heat, light or catalysts. 
(a) 
. .
:
sunlight
Energy
l C l C C l C l ? ? ? ? ? ?   
   
(b) 
. .
:
3
102
3
H C H H C H
k c al
? ? ? ? ? ? 
 
(c) 
(primary)
2 3
97
2 3
. .
H H C C H H C H C H
k c al
? ? ? ? ? ? ? ? ?   
 
(d)
) (secondary
3
3
94
3
3
. .
H H C
C H
C H
H C H
C H
C H
k c al
? ? ? ? ? ? ? 
 
 
(e) 
(tertiary)
3
3
3
91
3
3
3
. .
H C
C H
C H
C H
H C
C H
C H
C H
k c al
? ? ? ? ? ? ? 
 
(f) 
(allyl)
2 2
86
2 2
. .
H H C C H C H H C H C H C H
k c al
? ? ? ? ? ? ? ? ? ? ? 
 
(g)   ? ? ? ? ? ? ?
k c al
H C H
88
2
(benzyl)
2
. .
H H C ? ?  (h) 
2 3
/
2 3
. .
H N H C N H C H
l i ght h e at
? ? ? ? ? ? ? ? 
 
(ii) Free radicals are generally electrically neutral. 
 
(iii) There are seven electrons in the out most orbit of carbon of carbon free radicals. 
 
(iv) Owing to the presence of an odd electron; a carbon radical is paramagnetic in nature. Due to 
this reason free radicals are highly reactive. 
 
(v) Free radicals are neutral electrophiles. 
 
(vi) Chemical reactions which takes place with the formation of free radical as an intermediate 
are known as free radical reactions. These reactions takes place in three steps, 
 (a) Initiation  
 (b) Propagation and   
 (c) Termination 
 
Each of these steps, in turn, may involve two or more steps. 
(a) Initiation step: In this step, homolytic bond fission takes place in the presence of 
initiator, i.e., peroxide, h v , heat etc. The process is always endothermic. 
   l C l C C l C l
o r h v
. .
? ? ? ? ? ?
?
v e H ? ? ? 
(b) Propagation step: Propagation step is always two or more than two step process and 
all propagation steps should be exothermic, otherwise free radical reactions would 
not take place. 
Propagation step I: In this step, formation of free radical as reaction intermediate takes 
place. For example, 
 H C l H C l C H C H ? ? ? ? ? ?
3 3
. .
 ? ? H Negative 
 Propagation step II: Reaction intermediate reacts with reagent to give the product. 
 
 l C C l C H C l C l H C
. .
3 3
? ? ? ? ? ? ? ? ? H Negative 
 
(c) Termination step : In this step, free radical formed in the last propagation step 
(generally propagation step II) is destroyed by the addition of free radical or by the 
addition of some impurities like 
3
C H C l or 
4
C C l . 
   
2
. .
C l l C l C ? ? ? ? 
 Reaction velocity of free radical reaction is very-very high.  
 
Note: Certain compounds, known as inhibitor, retar velocity of free radical reactions. Common inhibitors 
are
2
O ,
2
I p-benzoquinone and diphenylamine. 
 
(2) Relative stabilities of free radicals: The tertiary alkyl free radicals are most stable and 
methyl free radial is least stable, i.e., the free radical formed easily has greater stability. 
 
radical Methyl 
radical free
Primary  
radical free
Secondary
radical free
Tertiary
|
. |
|
. |
|
. |
|
. |
H
H
C H
H
H
C R
H
R
C R
R
R
C R ? ? ? ? ? ? ? 
Benzyl and allyl free radicals are resonance stabilized hence are more stable than alkyl free 
radicals. 
   ? ? ? ?
2
.
H C ? ? ? ?
2
C H . ? ? ? ?
2
C H  
2
C H ? 
      
 
Benzyl free radical 
2 2 2 2
. .
C H C H H C H C C H C H ? ? ? ? ? ? ? (Allyl) 
Relative stability of free radicals are:  Benzyl > allyl >
o
3 >
o
2 >
o
1 > methyl, vinyl 
The stability of various free radicals can be compared from their bond dissociation energies (the 
energy required for the homolytic cleavage of the covalent bond in the molecule to form two 
. 
. 
Page 4


Reaction Intermediates.  
Short lived fragments called reaction intermediates result from homolytic and Heterolytic bond 
fission. The important reaction intermediates are free radicals, carbocations, carbonions, 
carbenes, benzyne and nitrenes. 
 
Free radicals 
A free radical may be defined as an atom or group of atoms having an odd or unpaired electron. 
These result on account of homolytic fission of a covalent bond and are denoted by putting a dot 
(.) against the symbol of atom or group of atoms. 
 ;
.
;
.
;
.
radical free
Methyl    
3
radical free
Hydrogen
radical free
Chlorine
C H H C l
r adi c al f r e e
E t hy l
H
H
C C H
. |
|
3
? ;        
radical
methyl Triphenyl
5 6
5 6
5 6
. |
|
H C
H C
C H C ? 
The first stable organic free radical was triphenyl methyl radical and it was prepared by 
Gomberg. 
 
(1) Characteristics of free radical. 
(i) The formation of free radical is initiated by heat, light or catalysts. 
(a) 
. .
:
sunlight
Energy
l C l C C l C l ? ? ? ? ? ?   
   
(b) 
. .
:
3
102
3
H C H H C H
k c al
? ? ? ? ? ? 
 
(c) 
(primary)
2 3
97
2 3
. .
H H C C H H C H C H
k c al
? ? ? ? ? ? ? ? ?   
 
(d)
) (secondary
3
3
94
3
3
. .
H H C
C H
C H
H C H
C H
C H
k c al
? ? ? ? ? ? ? 
 
 
(e) 
(tertiary)
3
3
3
91
3
3
3
. .
H C
C H
C H
C H
H C
C H
C H
C H
k c al
? ? ? ? ? ? ? 
 
(f) 
(allyl)
2 2
86
2 2
. .
H H C C H C H H C H C H C H
k c al
? ? ? ? ? ? ? ? ? ? ? 
 
(g)   ? ? ? ? ? ? ?
k c al
H C H
88
2
(benzyl)
2
. .
H H C ? ?  (h) 
2 3
/
2 3
. .
H N H C N H C H
l i ght h e at
? ? ? ? ? ? ? ? 
 
(ii) Free radicals are generally electrically neutral. 
 
(iii) There are seven electrons in the out most orbit of carbon of carbon free radicals. 
 
(iv) Owing to the presence of an odd electron; a carbon radical is paramagnetic in nature. Due to 
this reason free radicals are highly reactive. 
 
(v) Free radicals are neutral electrophiles. 
 
(vi) Chemical reactions which takes place with the formation of free radical as an intermediate 
are known as free radical reactions. These reactions takes place in three steps, 
 (a) Initiation  
 (b) Propagation and   
 (c) Termination 
 
Each of these steps, in turn, may involve two or more steps. 
(a) Initiation step: In this step, homolytic bond fission takes place in the presence of 
initiator, i.e., peroxide, h v , heat etc. The process is always endothermic. 
   l C l C C l C l
o r h v
. .
? ? ? ? ? ?
?
v e H ? ? ? 
(b) Propagation step: Propagation step is always two or more than two step process and 
all propagation steps should be exothermic, otherwise free radical reactions would 
not take place. 
Propagation step I: In this step, formation of free radical as reaction intermediate takes 
place. For example, 
 H C l H C l C H C H ? ? ? ? ? ?
3 3
. .
 ? ? H Negative 
 Propagation step II: Reaction intermediate reacts with reagent to give the product. 
 
 l C C l C H C l C l H C
. .
3 3
? ? ? ? ? ? ? ? ? H Negative 
 
(c) Termination step : In this step, free radical formed in the last propagation step 
(generally propagation step II) is destroyed by the addition of free radical or by the 
addition of some impurities like 
3
C H C l or 
4
C C l . 
   
2
. .
C l l C l C ? ? ? ? 
 Reaction velocity of free radical reaction is very-very high.  
 
Note: Certain compounds, known as inhibitor, retar velocity of free radical reactions. Common inhibitors 
are
2
O ,
2
I p-benzoquinone and diphenylamine. 
 
(2) Relative stabilities of free radicals: The tertiary alkyl free radicals are most stable and 
methyl free radial is least stable, i.e., the free radical formed easily has greater stability. 
 
radical Methyl 
radical free
Primary  
radical free
Secondary
radical free
Tertiary
|
. |
|
. |
|
. |
|
. |
H
H
C H
H
H
C R
H
R
C R
R
R
C R ? ? ? ? ? ? ? 
Benzyl and allyl free radicals are resonance stabilized hence are more stable than alkyl free 
radicals. 
   ? ? ? ?
2
.
H C ? ? ? ?
2
C H . ? ? ? ?
2
C H  
2
C H ? 
      
 
Benzyl free radical 
2 2 2 2
. .
C H C H H C H C C H C H ? ? ? ? ? ? ? (Allyl) 
Relative stability of free radicals are:  Benzyl > allyl >
o
3 >
o
2 >
o
1 > methyl, vinyl 
The stability of various free radicals can be compared from their bond dissociation energies (the 
energy required for the homolytic cleavage of the covalent bond in the molecule to form two 
. 
. 
radicals). In general, the smaller the amount of energy required for bond breaking, the more 
stable is the radical. 
 
(3) Structure of alkyl free radicals: The carbon atom of alkyl free 
radicals which is bonded to only three atoms or groups of atoms is 
2
s p hybridized. Thus, free radicals have a planar structure with odd 
electron situated in the unused p -orbital at right angles to the 
plane of hybrid orbitals. 
 
However, in the substituted alkyl radicals the ' ' s character of these 
orbitals has been found to increase, thus, tending to the pyramidal shape. 
 
3 2 2 3
. .
. .
F C H F C F H C H C ? ? ? .   
 So, 
3
C F is essentially pyramidal in shape. 
 
(4) Stereochemistry of free radicals:To learn about the stereochemistry of free radical reaction. 
We choose the reaction, chlorination of 1-chloro-2-methyl butane.  The reaction products are, 
 
 
 
 
 
If we review the insight of the reaction, it is clear that the reaction involves racemization at the 
reaction center. The free radical should have the 
2
s p hybridization.  Obviously a 
2
C l molecule 
could attack either the upper or lower lobe of the p -orbital with equal chances, leading to 
racemic mixture. 
Intermediate 
%) 50 ( %) 50 (
form form
2
? ? ? ? ? ? ? l d
C l
 
 
 
(5) Reactions involving free radicals, 
 (i) Chlorination of alkanes   
 (ii) Pyrolysis of alkanes   
 (iii) Wurtz reaction 
C
 
Et
 
H
 
Me
 
CH
2
Cl 
C
 
Et
 
Cl
 
Me
 
CH
2
Cl 
h v
C l
? ? ? ?
2
+
 
C
 
Et
 
Cl
 
Me
 
CH
2
Cl 
C 
Free or unpaired  
electron 
120 ? 
? 
p-orbital 
Sp
2
 hybridised c-atom 
Page 5


Reaction Intermediates.  
Short lived fragments called reaction intermediates result from homolytic and Heterolytic bond 
fission. The important reaction intermediates are free radicals, carbocations, carbonions, 
carbenes, benzyne and nitrenes. 
 
Free radicals 
A free radical may be defined as an atom or group of atoms having an odd or unpaired electron. 
These result on account of homolytic fission of a covalent bond and are denoted by putting a dot 
(.) against the symbol of atom or group of atoms. 
 ;
.
;
.
;
.
radical free
Methyl    
3
radical free
Hydrogen
radical free
Chlorine
C H H C l
r adi c al f r e e
E t hy l
H
H
C C H
. |
|
3
? ;        
radical
methyl Triphenyl
5 6
5 6
5 6
. |
|
H C
H C
C H C ? 
The first stable organic free radical was triphenyl methyl radical and it was prepared by 
Gomberg. 
 
(1) Characteristics of free radical. 
(i) The formation of free radical is initiated by heat, light or catalysts. 
(a) 
. .
:
sunlight
Energy
l C l C C l C l ? ? ? ? ? ?   
   
(b) 
. .
:
3
102
3
H C H H C H
k c al
? ? ? ? ? ? 
 
(c) 
(primary)
2 3
97
2 3
. .
H H C C H H C H C H
k c al
? ? ? ? ? ? ? ? ?   
 
(d)
) (secondary
3
3
94
3
3
. .
H H C
C H
C H
H C H
C H
C H
k c al
? ? ? ? ? ? ? 
 
 
(e) 
(tertiary)
3
3
3
91
3
3
3
. .
H C
C H
C H
C H
H C
C H
C H
C H
k c al
? ? ? ? ? ? ? 
 
(f) 
(allyl)
2 2
86
2 2
. .
H H C C H C H H C H C H C H
k c al
? ? ? ? ? ? ? ? ? ? ? 
 
(g)   ? ? ? ? ? ? ?
k c al
H C H
88
2
(benzyl)
2
. .
H H C ? ?  (h) 
2 3
/
2 3
. .
H N H C N H C H
l i ght h e at
? ? ? ? ? ? ? ? 
 
(ii) Free radicals are generally electrically neutral. 
 
(iii) There are seven electrons in the out most orbit of carbon of carbon free radicals. 
 
(iv) Owing to the presence of an odd electron; a carbon radical is paramagnetic in nature. Due to 
this reason free radicals are highly reactive. 
 
(v) Free radicals are neutral electrophiles. 
 
(vi) Chemical reactions which takes place with the formation of free radical as an intermediate 
are known as free radical reactions. These reactions takes place in three steps, 
 (a) Initiation  
 (b) Propagation and   
 (c) Termination 
 
Each of these steps, in turn, may involve two or more steps. 
(a) Initiation step: In this step, homolytic bond fission takes place in the presence of 
initiator, i.e., peroxide, h v , heat etc. The process is always endothermic. 
   l C l C C l C l
o r h v
. .
? ? ? ? ? ?
?
v e H ? ? ? 
(b) Propagation step: Propagation step is always two or more than two step process and 
all propagation steps should be exothermic, otherwise free radical reactions would 
not take place. 
Propagation step I: In this step, formation of free radical as reaction intermediate takes 
place. For example, 
 H C l H C l C H C H ? ? ? ? ? ?
3 3
. .
 ? ? H Negative 
 Propagation step II: Reaction intermediate reacts with reagent to give the product. 
 
 l C C l C H C l C l H C
. .
3 3
? ? ? ? ? ? ? ? ? H Negative 
 
(c) Termination step : In this step, free radical formed in the last propagation step 
(generally propagation step II) is destroyed by the addition of free radical or by the 
addition of some impurities like 
3
C H C l or 
4
C C l . 
   
2
. .
C l l C l C ? ? ? ? 
 Reaction velocity of free radical reaction is very-very high.  
 
Note: Certain compounds, known as inhibitor, retar velocity of free radical reactions. Common inhibitors 
are
2
O ,
2
I p-benzoquinone and diphenylamine. 
 
(2) Relative stabilities of free radicals: The tertiary alkyl free radicals are most stable and 
methyl free radial is least stable, i.e., the free radical formed easily has greater stability. 
 
radical Methyl 
radical free
Primary  
radical free
Secondary
radical free
Tertiary
|
. |
|
. |
|
. |
|
. |
H
H
C H
H
H
C R
H
R
C R
R
R
C R ? ? ? ? ? ? ? 
Benzyl and allyl free radicals are resonance stabilized hence are more stable than alkyl free 
radicals. 
   ? ? ? ?
2
.
H C ? ? ? ?
2
C H . ? ? ? ?
2
C H  
2
C H ? 
      
 
Benzyl free radical 
2 2 2 2
. .
C H C H H C H C C H C H ? ? ? ? ? ? ? (Allyl) 
Relative stability of free radicals are:  Benzyl > allyl >
o
3 >
o
2 >
o
1 > methyl, vinyl 
The stability of various free radicals can be compared from their bond dissociation energies (the 
energy required for the homolytic cleavage of the covalent bond in the molecule to form two 
. 
. 
radicals). In general, the smaller the amount of energy required for bond breaking, the more 
stable is the radical. 
 
(3) Structure of alkyl free radicals: The carbon atom of alkyl free 
radicals which is bonded to only three atoms or groups of atoms is 
2
s p hybridized. Thus, free radicals have a planar structure with odd 
electron situated in the unused p -orbital at right angles to the 
plane of hybrid orbitals. 
 
However, in the substituted alkyl radicals the ' ' s character of these 
orbitals has been found to increase, thus, tending to the pyramidal shape. 
 
3 2 2 3
. .
. .
F C H F C F H C H C ? ? ? .   
 So, 
3
C F is essentially pyramidal in shape. 
 
(4) Stereochemistry of free radicals:To learn about the stereochemistry of free radical reaction. 
We choose the reaction, chlorination of 1-chloro-2-methyl butane.  The reaction products are, 
 
 
 
 
 
If we review the insight of the reaction, it is clear that the reaction involves racemization at the 
reaction center. The free radical should have the 
2
s p hybridization.  Obviously a 
2
C l molecule 
could attack either the upper or lower lobe of the p -orbital with equal chances, leading to 
racemic mixture. 
Intermediate 
%) 50 ( %) 50 (
form form
2
? ? ? ? ? ? ? l d
C l
 
 
 
(5) Reactions involving free radicals, 
 (i) Chlorination of alkanes   
 (ii) Pyrolysis of alkanes   
 (iii) Wurtz reaction 
C
 
Et
 
H
 
Me
 
CH
2
Cl 
C
 
Et
 
Cl
 
Me
 
CH
2
Cl 
h v
C l
? ? ? ?
2
+
 
C
 
Et
 
Cl
 
Me
 
CH
2
Cl 
C 
Free or unpaired  
electron 
120 ? 
? 
p-orbital 
Sp
2
 hybridised c-atom 
 (iv) Anti-markownikoff rule  
 (v) Kolbe electrolytic synthesis  
 (vi) Polymerization initiated by free radical. 
 
 
Carbonium ions (carbocations) 
Carbocation is defined as a group of atoms which contain positively charged carbon having only 
six electrons. It is obtained by Heterolytic fission of a covalent bond involving carbon atom. It is 
denoted by putting a positive charge (+) against the symbol of group of atoms.  
?
3
C H 
?
5 2
H C 
?
C H C H
2 3
) ( 
?
C C H
3 3
) ( 
Methyl carbonium ion Ethyl carbonium ion Isopropyl carbonium 
ion 
Tert. Butyl carbonium ion 
Primary Secondary Tertiary 
 
 
(1) Characteristics of carbocations 
 (i) The formation of carbocations can be done, 
 (a) By heterolysis of halogen compounds: l C C C H C l C C H
?
? ? ? ? ? ?
?
3 3 3 3
) ( ) ( 
 (b) By protonation of alkenes or alcohols:
2 2
C H C H ? ?
3 2
C H H C ?
?
 
       H O R ? ? ?
2
H O R
?
? ? O H R
2
?
?
 
 (c) By decomposition of Diazo compounds:
2 5 6
2
5 6 2 5 6
2
N H C N H C C l N H C
N C l
? ? ? ? ? ? ? ? ? ? ?
?
?
?
?
 
 (ii) Carbocations are not electrically neutral. 
(iii) There are six electrons in the out most orbit of carbon of carbocation i.e., 2 electrons 
less than octet. 
 (iv) A carbocation is diamagnetic in nature due to all paired electrons. 
(v) Carbocations are charged electrophiles i.e., they react with nucleophilic reagents. The 
order of reactivity of carbocations is, Primary (1
o
) > Secondary (2
o
) > Tertiary (3
o
) 
 
(2) Types of carbocations: Carbocations can be classified into the following types, 
 (i) Alkyl carbocations 
H
?
 
H
?
 
–H 2 O