c) Explain the influence of ortho-para and meta directing substituents towards electrophilic aromatic substitution
reaction.
d) Predict the product of electrophilic aromatic substitution of monosubstituted benzene.
*limit to reaction in 6.3(a) only
a) Explain the electrophilic aromatic substitution reaction of benzene:
i. nitration;
ii. halogenation;
iii. Friedel-Crafts alkylation; and
iv. Friedel-Crafts acylation.
-NO2
-X ( X = Cl, Br )
-R ( R = alkyl)
-C=O
C3
(i) predict the products in an electrophilic substitution reaction
when the substituted group in benzene is electron accepting or
electron donating;
STPM

A substituent on the benzene ring affects 2 aspects of electrophilic
aromatic substitution :
1. Reaction rate
2. Orientation
c) Explain the influence of ortho-para and meta directing substituents towards
electrophilic aromatic substitution reaction.
1. Effect of Substituents on Electrophilic Aromatic Substitution

Effect of substituent
1. Reaction rate 2. Orientation
i. Activating ii. Meta
ii. Deactivating i. Ortho-para

1. Reaction Rate
• A substituted benzene reacts faster or slower towards further
substitution.
• Example: more reactive or less reactive

i. Activating Groups (activators)
• Activate the benzene ring towards electrophilic attack, making it
more reactive than benzene via Inductive Effect or Resonance Effect.
• Electron-donating groups / electron-releasing groups are activating
groups

Benzene rings that contain an electron-donating group (activating group):
CH3
OH NH2
Alkyl group activates the benzene ring
via Inductive Effect
Hydroxy and amino groups activate
the benzene ring via Resonance Effect
Example

ii. Deactivating Groups (deactivators)
• Deactivate a benzene ring towards electrophilic attack, making it
less reactive than benzene.
• Electron-withdrawing groups are deactivating groups.

Benzene rings that contain an electron-withdrawing group (deactiving group):
Cl CN COOH
Example

Relative rate
of nitration
reactivity
Activating group
Deactivating group
1000
OH
H NO2
HNO3
, H2
SO4
50-55 °C
Nitro compound
0.033
Cl
1
H
Example

2. Orientation
The existing substituent on the benzene ring determines the position
of the second substituent.
A = substituent
A
ortho
meta
para
ortho
meta

A
+ E+
A = ortho-para
director
A = meta
director
A
E
+
A
E
A
E
1, 2- (ortho) 1, 4- (para)
1, 3- (meta)

Example
ethylbenzene
Ortho and para isomers
i. Ortho-para director
Br
CH2
CH3
CH2
CH3
CH2
CH3
Br
+
Br2
, FeBr3

ii. Meta director
nitrobenzene
NO2
NO2
NO2
conc. HNO3
, conc. H2
SO4
100 °C

1. All ortho-para directors (except halogens)  activating groups.
2. All meta directors  deactivating groups.
3. The halogens are ortho-para directors but deactivating groups.
Thus,

Ortho-para directors which are activating groups
—NH2
●●
—R
—NHCOR
●●
—OR
●●
●●
—OH
●●
●●
—NHR
●●
—NR2
●●
Increasing ring activation
General structure
—R or —Z
Alkyl
(Inductive effect)
have lone
pair electron
(Resonance effect)
●
●

Ortho-para directors which are deactivating groups
—F
●●
●
●
●●
—Cl
●●
●
●
●●
—Br
●●
●
●
●●
— I
●●
●
●
●●
Geneal structure :
—X (halogens)
●
●
●
●
●
●

Meta director which are deactivating groups
—CHO
Increasing ring deactivation
General structure:
—Y (d+ or + )
—COR
—COOR
—COOH
—CN
—SO3H
—NO2
—NR3
+
partial
charge
full
charge