1. SUBSTITUTION &
ELIMINATION REACTIONS

2. SUBSTITUTION REACTIONS
Substitution Reactions
Reactions where an atom or side-chain is
replaced by a different atom or side-chain.
H3C-X + H2O  CH3OH + HX
X
+ X2  + HX

3. SUBSTITUTION REACTIONS
Substitution Reactions
Identify the substitution reaction(s):
a) Heat
+ Br2  Br + HBr
UV
Substitution
b) FeBr3
+ Br2  Br + HBr
Br Substitution
Room
c) temperature
+ Br2  Br
Halogenation

4. SUBSTITUTION REACTIONS
Substitution Reactions
Nitric acid may react with benzene to
substitute an H with a –NO2 (nitro) group.
H2SO4
+ HNO3  NO2 + H2O

5. SUBSTITUTION REACTIONS
Substitution Reactions
Alkyl groups may also be added to benzene
groups.
AlCl3
+ CH3CH2Cl  CH2CH3 + HCl

6. SUBSTITUTION REACTIONS
Example #1
Predict the product formed when benzene
reacts with chloromethane in the presence
of AlCl3 catalyst.
AlCl3
+ CH3Cl  CH3 + HCl

7. SUBSTITUTION REACTIONS
Substitution Reactions
At first, only a single H group will be
substituted in any reaction involving a
cyclic or aromatic hydrocarbon.
Additional substitutions on an aromatic ring
will have preferences for location.

8. SUBSTITUTION REACTIONS
Second Aromatic Substitution
When another group is added to an
aromatic ring, rules determine the
preferred location of the second
group.
Br + Br2 
Br Br
Br Br Br Br
ortho meta para

9. SUBSTITUTION REACTIONS

10. SUBSTITUTION REACTIONS

11. SUBSTITUTION REACTIONS
Position depends on the substituent involved
Y in % Ortho- % Meta- % Para-
Reaction
C6H5–Y Product Product Product
–O–CH3 Nitration 30–40 0–2 60–70
–O–CH3 F-C Acylation 5–10 0–5 90–95
–NO2 Nitration 5–8 90–95 0–5
–CH3 Nitration 55–65 1–5 35–45
–CH3 Sulfonation 30–35 5–10 60–65
–CH3 F-C Acylation 10–15 2–8 85–90
–Br Nitration 35–45 0–4 55–65
–Br Chlorination 40–45 5–10 50–60

12. SUBSTITUTION REACTIONS
In the case of NH2 as a substituent, ortho and para are favoured
because of the stability of the reaction intermediate:
4 resonance
structures
3 resonance
structures
4 resonance
structures

13. SUBSTITUTION REACTIONS
Position depends on the substituent involved
The rate of substitution determines which
product is favoured

14. SUBSTITUTION REACTIONS
Amines are prepared by reacting alkyl
halides with NH3.
CH3CH2-I + NH3  CH3CH2-NH2 + HI
2° and 3° amines are produced with the
addition of more alkyl halide reactants.
Homework:
p30 #4, 6
p31 #1- 3a-c

15. ELIMINATION REACTIONS

16. ELIMINATION REACTIONS
Two adjacent atoms or side groups are
removed resulting in a double bond.
Conc.
H2SO4
CH3CHOHCH3  CH3CH=CH2 + H2O
The reverse reaction is an addition reaction.
Homework:
p44 #7,8