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several ways which lead to different functional groups. The reactions in
Figure 7.1
are arranged to allow us to easily see these relationships.
7.2 ALKANES
With any compound class, if you understand the functional group bonding, you
will have an idea of its reactivity. Alkanes have no clear reactive feature. They
show no great bond polarity and have only strong C-C (347 kJ/mol) and C-H
(414 kJ/mol) σ-bonds. This explains their very low reactivity. In fact, they are
widely used as solvents. However, under special conditions they can be reacted
with oxygen and chlorine.
FIGURE 7.1
Selected functional group interconversions.
7.2.1 Oxidative Combustion
A
combustion
reaction occurs when saturated hydrocarbons are burned in the
presence of oxygen. Examples include combustion engines or furnaces. The effi-
ciency of combustion is controlled by the oxygen supply. If enough oxygen is
supplied, the products are carbon dioxide, water, and lots of heat energy.
CH
4
+2O
2
→CO
2
+2H
2
O[+800kJ/mol]
2C
4
H
10
+13O
2
→8CO
2
+10H
2
O[+2877kJ/mol]
If the oxygen supply is limited, the combustion is not complete. As seen in
the following equations, this gives carbon monoxide and carbon deposits.
2CH
4
+3O
2
→2CO+4H
2
O[toxicexhaustfumes]
CH
4
+O
2
→C+2H
2
O[carbondeposits]
7.2.2 Radical Chlorination
In ultraviolet light, alkanes react with chlorine in a radical substitution reaction.
This is one of the only radical reactions shown in this topic. It is a good example
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