Comparison Of Ease Of Chlorination - Benzene, Methylbenzene And Nitrobenzene

An easy to follow explanation of the relative ease of reactivity of benzene, methylbenzene and nitrobenzene which can be used to answer more than one CAPE Unit 2 chemistry question, including one from the 2013 exam paper.

1. COMPARING EASE OF CHLORINATION*
~BENZENE, METHYLBENZENE AND NITROBENZENE ~
Created by Denison at Global in Cunupia. 739‐2656.
(*this halogenation occurs by electrophilic 
(aromatic) substitution and starts 
with the Cl
+
electrophile)
Activating substituents make the benzene 
ring more reactive toward electrophilic 
substitution, e.g. ‐CH
3
in methylbenzene.
Deactivating substituents make the benzene 
ring less reactive toward electrophilic 
substitution, e.g. –NO
2
in nitrobenzene.
Substituents
can be strongly
, moderately 
or weakly activating
or deactivating
.
CH
isweaklyactivating
while
NO
isstronglydeactivating
This
Remember that activating substituents 
donateelectrons into the ring and 
deactivating substituents withdraw
electrons from the ring.
–
CH
3
is
 weakly
 activating
while
 –
NO
2 
is
 strongly
 deactivating
. 
This
  
means  that –NO
2
withdraws electrons from the ring to a greater extent 
than –CH
3
donates them. Therefore nitrobenzene is deactivated to a 
greater degree than methylbenzene is activated, compared to the base 
case, which is benzene.