A helpfull topic for people studying chemistry, for PU, cet, bsc, etc,

1. TYPES OF ORGANIC
CHEMICAL REACTIONS

2. Categories of Simple Organic
Reactions
• Substitution
• Addition
• Condensation/elimination
• Hydrolysis
• Mild oxidation & strong oxidation
• Combustion
• Acid/base reactions

3. Substitution Reactions
A substitution reaction occurs whenever one
atom of an organic molecule is replaced
by another.
Substitution reactions often require heat
and/or a catalyst in order to occur.
Example: Substitution of an alkane
H H
H C H + Cl2 H C Cl + HCl
H H
HEAT
 

4. Substitution of Benzene
FeBr catalyst3..
 
Due to the strong bonding arrangement between the carbon atoms
in a benzene ring, the ring cannot be easily broken during
chemical changes. The hydrogen atoms that are bonded to each
carbon can be substituted for other atoms and groups.
Examples:
+ Br2
+ HBr
BrH
+ HNO3
H SO2 4
  NO2 + H2O
TNT synthesis…

5. Addition Reactions
• In addition reactions, new atoms or groups are
bonded to the atoms of an organic molecule.
The organic molecule must be unsaturated to
start with (double or triple bonds!)
• New bonds can be made to the carbon atoms
involved in the double or triple bond if the part
of the bond is first broken.

CH2=CH2
breakpibond
 
I’m now ready
to make more
bonds!
C C
H
H
H
H


6. Some Simple Addition Reactions
C=C
H H
H H
+ H2  H-C-C-H
H H
H H
(a.k.a. “hydrogenation”)
C=C
H H
H H
+ HCl  H-C-C-Cl
H H
H H
C=C
H H
H H
+ H2O  H-C-C-OH
H H
H H
(a.k.a. “hydrolysis”)

7. Testing for unsaturated
hydrocarbons
• Unsaturated hydrocarbons can be
identified by their reaction with aqueous
bromine, Br2(aq).
Demo!
C=C
H H
H H
+ Br2  Br-C-C-Br
H H
H H
(deep orange)  (colourless)
Completely saturated molecules DO NOT react
in this manner- thus the orange colour remains.

8. Markovnikov’s Rule
• If the double or triple bond is part of a molecule
with three or more carbon atoms in the chain,
the most likely addition reaction products can be
predicted using a rule first formulated by the
Russian chemist V.V. Markovnikov.
Markovnikov’s Rule
…the more electronegative atom will
predominantly bond to the carbon atom of
the double bond that has fewer hydrogen
atoms.

9. Markovnikov’s Rule
C=C-CH3
H
H H
+ H2O 
H- C - C- CH3
H
HH
OH
It should be mentioned that the primary
alcohol (1-propanol) is also a possibility, but
it would be produced in a much lower
proportion than the 2-propanol shown
above.
H-C C-CH2-CH3 + 2HCl  H-C C-CH2-CH3-
Cl
Cl
H
H
Most favoured product!
Eg.1
Eg.2

10. Condensation/Elimination
Reactions
• Organic compounds containing hydroxyl or
carboxyl groups can combine by eliminating a
molecule of water between them.
Example 1- condensation of two alcohols
H-C - C-O-H
H
H
H
H
+ H-O-C - C-H
H
H
H
H
Molecule of H2O is formed
H SO2 4
  H-C - C-O-C–C-H
H
H
H
H
H
H
H
H
+ H2O
An ether is created!

11. Condensation/elimination
• When an alcohol reacts with a carboxylic acid to
eliminate a molecule of water between them, the
resulting bond creates an ester linkage as
shown below:
H-C - C-O-H
H
H
H
H
H-O-C – CH2-CH3
O
+
CH2-CH2- O- C-CH2-CH3
O
+
H2O
We’ve created an ester
If excess water is
added to an ester, the
reaction will reverse
itself.

12. Uses of Esters
• Esters often have characteristic flavours and
aromas which allows them to be used in food
products.
• Methanol + butanoic acid  methyl butanoate (apples)
• Octanol + acetic acid  octyl acetate (orange)
• Benzyl alcohol + butanoic acid  phenyl butanoate (flowers)
• Pentanol + acetic acid  pentyl acetate
Demo!

13. Condensation/elimination
• If a molecule of water is eliminated from within a
single molecule, an unsaturated compound is
formed and the molecule is said to be
“dehydrated.”
H
OH
H SO2 4
 
H
H
H
H
+ H2O

14. Oxidation Reactions
• In the terminology of organic chemistry, when a
molecule is oxidized, the number bonds to oxygen
atoms increases within the molecule.
• Oxidizing agents are varied: CrO3/H+, KMnO4,
K2Cr2O7
• Often, the oxidizing agent is represented simply
as “O” over the reaction arrow:
O
 

15. Oxidation Reactions
Mild Oxidation
1o alcohol mild O..
  aldehyde
CH3-C-OH
H
H
mild O..
 
ethanol
CH3-C-H
O
ethanal
Strong Oxidation
1o alcohol strong O..
  Carboxylic acid
CH3-C-OH
H
H
strong O..
  CH3-C-OH
O
Ethanoic acid

16. Oxidation Reactions
Strong Oxidation cont’d…
• Secondary alcohols require a strong oxidizing
agent and can only be oxidized to ketones.
CH3-C-CH2-CH3
O
butanone
•Tertiary alcohols DO NOT undergo oxidation. Why not?
CH3-C-CH2-CH3
H
OH
2-butanol
strong O..
 
OH
CH3-C-CH3
CH3
2-methyl-2-propanol
strong O..
  NO REACTION
DEMOS!

17. Combustion
• All organic compounds can be combusted or
burned. Carbon dioxide gas and water vapour
are the products of hydrocarbon combustion.
• Combustion is really a type of very extreme
oxidation reaction where O2(g) is the oxidizing
agent.
2C2H2(g) + 5O2(g)  4CO2(g) + 2H2O(g)
CH3-CH2-OH(l) + 3O2(g)  2CO2(g) + 3H2O(g)
BOOM!

18. Reactions of Organic Acids
• Like inorganic acids such as HCl(aq), organic
acids react with bases to produce liquid water
and a salt.
Example:
C-O-H
O
Benzoic acid
+ NaOH 
C-O1-Na1+
O
Sodium benzoate
+ H2O