Reactions with Alkanes
A. The alkanes undergo complete and incomplete combustions. Approximately 95% of crude oil serves as
combustibles.
CH4(g) + 2 O2(g)

2 C3H8(g) + 7 O2(g)
CO2(g) + 2 H2O(g)
complete combustion
CO2(g) + 8 H2O(g) + 4 CO(g) + C(s)

incomplete combustion
B. The alkanes also undergo substitution reactions  substitute hydrogen one at a time for halogens or <<nitro>>
forming organo-halides and another product
H
l
H-C-H
l
H
H
l
H - C - Cl
l
H
+
Cl – Cl
+
Cl - Cl
H
l
H - C - Cl
l
H


+
H
l
H - C - Cl
l
Cl
HCl
+
This also occurs with other
halogens (F2, Br2, I2) and H-OH
& H-NO2.
HCl
etc.
C. Cracking was first introduced in Sarnia, Ontario. This process uses heat (or catalysts) to break larger hydrocarbon
molecules into smaller gasoline molecules. Cracking is done in the absence of air and can produce different types
of hydrocarbons.
C17H36(l)

C9H20(l)
+
C8H16(l)
D. Reforming is another technique that uses heat, pressure, and catalysts to convert straight chain alkanes to
branched chains and also convert cyclic alkanes into aromatic compounds.
C5H12(l)
+
C5H12(l)

C10H22(l)
+
H2(g)
Reactions with Alkenes
A. The alkenes also undergo complete and incomplete combustions as the alkanes.
B. The alkenes can be formed during cracking.
C2H5OH(l)
acid


C2H4(g) + H2O
C. In an addition reaction, atoms are added to a multiple bond. One bond of the multiple bond breaks so that two new
bonds can form.
H
H
\
/
C=C
/
\
+
Br - Br

H H
l
l
H-C-C-H
l
l
This also occurs with other
halogens (F2, Cl2, I2) and H-OH &
H-NO2 and H2.
H
H
H
H
\
/
C=C
/
\
H
H
+
H
H
\
/
C=C
/
\
H
H
H-H
+

H - OH
Br Br
H H
l
l
H-C-C-H
l
l
H H
H H
l
l
H-C-C-H
l
l
H OH

This is known as hydrogenation.
This is one formation for
alcohols.
D. Alkenes also undergo additional polymerization: a reaction in which monomers with double bonds are joined
together, through multiple addition reactions, to form a polymer (chain). Various products such as polyester,
polystyrene, latex, polyethylene, and polyvinylchloride are produced in this method.
n
H
H
\
/
C=C
/
\
H
H

ethene
(ethylene)
H H
l
l
-C–Cl
l
H H
n
n represents the number of alkenes with ruptured bonds
allowing the formation of the polymer chain.
polyethylene
(plastic)
Reactions with Alkynes
A. The alkynes will also undergo complete and incomplete combustions as the alkanes and alkenes.
B. The alkynes also demonstrate addition reactions as the alkenes.
H–CC–H
Cl Cl
l
l
H–C=C–H
H–CC–H
+
+
+
Cl – Cl
Cl – Cl
2H–H

Cl Cl
l
l
H–C=C-H

Cl
l
H–C–
l
Cl
Cl
l
C–H
l
Cl

H
l
H–C–
l
H
H
l
C–H
l
H
This also occurs with other
halogens (F2, Br2, I2) and H-OH
& H-NO2. One bond at a time.