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Types of Organic Reactions
Most organic compounds that are commercially available are derived from plants.
Plants are the ultimate chemists. In order for scientists to recreate compounds we
must be able to take a starting compound and manipulate it until we have created
the compound we are interested in.
There are certain types of reactions in organic chemistry. These will provide us
with the different pathways that we can later use to move from one organic family
to another.
1. Combustion
The reaction of a substance with oxygen, producing oxides and energy.
Example:
Alkane + oxygen  carbon dioxide + water
CH4[g] + 2 O2[g] -> CO2[g] + 2 H2O[g] + energy
2. Substitution Reactions
This is a chemical reaction that breaks apart a carbon-hydrogen bond and replaces
the hydrogen atom with another atom or atom group.
Example:
Alkane + halogen  alkyl halide
H H H
| | |
H-C-C-C-H + Br-Br
| | |
H H H
H H H
| | |
=> H-C-C-C-H
| | |
Br H H
+
H-Br
propane + bromine => 1-bromopropane + hydrogen bromide
Addition Reactions
Hydrogen or a halogen is added to an alkene or alkyne at the double or triple
bond.
a) Hydrogenation
Hydrogenation is an addition reaction involving the combination of hydrogen with
unsaturated hydrocarbons.
Example:
H H H H
H H H H
| | | |
| | | |
H-C=C-C-C-H + H-H => H-C-C-C-C-H
| |
| | | |
H H
H H H H
butene + 2H
=>
butane
C3H4
+ 2H-H =>
C3H8
propyne + 2H-H => propane
b) Halogenation (with Br2 or Cl2)
Halides also have the ability to add halogens to the carbons of double or triple
bonds creating organic halides.
Example:
H H
H H
| |
| |
H-C=C-H + Cl-Cl => H-C-C-H
| |
Cl Cl
ethene + chlorine => 1,2-dichlororethane
C2H2 + Cl-Cl
=> C2H2B2
ethyne + bromine => 1,2-dibromoethene
c) Hydrohalogenation (with hydrogen halides)
d) Hydration (with water)
Elimination
Elimination is a chemical reaction in which an atom or group of atoms is removed
from the larger molecule.
Example:
H H H
| | |
H-C-C-C-H + OH
| | |
H Br H
=>
H H H
| | |
H-C=C-C-H
|
H
2-bromopropane + hydroxide ion
=>
+
propene
H-O
|
H
+
+
Br
water + bromide ion
Alcohols could also undergo elimination reactions by reacting with an acid to
remove a hydrogen atom and a hydroxyl group thus producing alkenes.
Example:
H H
| |
H-C-C-H
| |
H OH
+
acid =>
H H
| |
H-C=C-H
|
H
ethanol
+
acid =>
ethene
+
+
H-O
|
H
water
Condensation
Condensation is an organic reaction when two molecules combine, usually in the
presence of a catalyst, with the elimination of water or some other simple
molecule. Catalysts commonly used in condensation reactions include acids and
bases. The combination of two identical molecules is known as self-condensation.
This process forms larger molecules, many of which are useful in organic
synthesis. Aldehydes, ketones, esters, alkynes, and alcohols are among several
organic compounds that combine with each other to form larger molecules.
Example:
CH3OH
methanol
+
+
CH3OH
methanol
=>
=>
CH3OCH3
+
HOH
methoxymethane + water
For a carboxylic acid undergoing condensation reaction, it combines with another
reactant, forming two products - an organic compound and the byproduct of water.
In an event when a carboxylic acid reacts with an alochol to produce an ester and
water, this process is called esterification.
Example:
CH3COOH
ethanoic acid
water
+
HOCH3
+
methanol
=>
=>
CH3COOCH3
+
methyl ethanoate
HOH
+