reactions

1. SUBSTITUTION &
ELIMINATION REACTIONS

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

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

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

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

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

7. Substitution ReactionsSubstitution 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.
SUBSTITUTION REACTIONS

8. 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
BrBr
ortho meta para
SUBSTITUTION REACTIONS

9. SUBSTITUTION REACTIONS

10. SUBSTITUTION REACTIONS

11. Y in
C6
H5
–Y
Reaction
% Ortho-
Product
% Meta-
Product
% Para-
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
–Cl Chlorination 40–45 5–10 50–60
Position depends on the substituent involved
SUBSTITUTION REACTIONS

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

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

14. 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.
SUBSTITUTION REACTIONS

15. Substitution: Alcohols
This reaction with the Lucas Reagent (ZnCl2) is a qualitative
test for the different types of alcohols
The difference in rates of reaction is due to the solubility of
the resulting alkyl halides:
- 3° → turns cloudy immediately
- 2° → turns cloudy after 5 minutes
- 1° → longer than 5 minutes to turn cloudy
Lucas Reagent
ZnCl2
CH3CH2OH + HCl CH3CH2Cl + H2O
alcohol + hydrogen halide alkyl halide + water
ZnCl2
SUBSTITUTION REACTIONS

16. Substitution: Alcohols
With Sodium as a reactant
• When they react as an acid, the alkyl oxide ion (R-CH2O-
) is
formed:
• This reaction also occurs to esters in a process called
saponification
ethanol + sodium ethoxide ion + sodium ion + hydrogen
2 CH3CH2OH + 2 Na 2 CH3CH2O-
+ 2 Na+
+ H2
ester + water alcohol + carboxylate ion
C
O
-O
++ H2O
Basic Solution
C H
H
O
H C
H
H
H
C
O
C
H
H
H
C
H
H
H
O
methanolmethylethanoate
(methylacetate)
H
NaOH
Na+
sodium ethanoate
(sodium acetate)
SUBSTITUTION REACTIONS

17. ELIMINATION REACTIONS

18. Two adjacent atoms or side groups are
removed resulting in a double bond.
CH3CHOHCH3  CH3CH=CH2 + H2O
The reverse reaction is an addition reaction.
Conc.
H2SO4
ELIMINATION REACTIONS