• Use your understanding of sigma and pi bonds
to explain why alkenes are more reactive than
alkanes.
• Objective: To observe the results of a bromine
water test and an iodine test with hexanes and
with vegetable oil.
• What do you know about the structures of these
two species and about bromine and iodine’s
behavior in hexane?
1. Put about 1 cm3 of the hexanes to a small test
tube.
2. Add 3-5 drops of bromine water solution.
Record initial color.
3. Stopper and shake. Record final color.
4. Add about 1 cm3 of vegetable oil.
5. Stopper and shake. Record final color.
6. Repeat steps 1-5 with Iodine instead of
bromine.
• Summarize your results.
• Explain the difference in the bromine and
iodine test with hexanes vs. vegetable oil.
• What are unsaturated hydrocarbons?
• Alkenes/alkynes
• Have double or triple bonds.
• All carbons have NOT maxed out their number of
C-H bonds.
• More reactive than alkanes
• Why?
• More energetically favorable to be all single bonds
• Think bond enthalpies
• Low activation energy to saturate alkenes
• Important starting points for synthesis of other
compounds
• Double bond(s)  single bonds
• Two new bonds formed
• Alkenes react readily with chlorine or bromine
to create a di-halo-alkane (what is this?):
C2H4 + Cl2 → CH2Cl CH2Cl
H
H
H
H
+
Cl Cl
Cl Cl
H
H
H H
• Alkenes react readily with hydrogen halides to
create a halo-alkane :
http://www.youtube.com/watc
h?v=5GQelnluHzE
C2H4 + HBr → CH3CH2Br
H
H
H
H
+
H Cl
H Cl
H
H
H H
• Addition of hydrogen with nickel catalyst
• How does it work?
• If alkene or alkyne present:
• Bromine water = rust color
• Will turn colorless
• Why?
• Remember that H2O is the same as HOH, which
can be dissociated into H+ and OHH
H
H
H
H H
acid
+
H
O
H
H
O
H H
H
• Reversible
• High temperatures/pressures (300 ⁰C, 7atm) 
alcohol
• Lower temperatures/pressures  alkene and water
•
•
Naming polymers: put “poly-” in front of the
name of the monomer
There are 3 polymerization mechanisms that
you need to be familiar with:
1. Polyethene
2. Polychloroethene
3. Polypropene
•
•
•
Reaction: nCH2=CH2 [-CH2-CH2-]n
Monomer: ethene (aka ethylene), CH2=CH2
Conditions:
•
•
•
Temp: 200º C
Pressure: 2000 atm
Initiator: O2
• Each chloroethene contains 1 chlorine
• Therefore, when the chloroethene
molecules polymerize, every
other carbon will bond to 1 chlorine
• Aka PVC
+
=
Ethene can be used for a variety of purposes:
• Steam → ethanol
• Polymerize → polyethene
• React with chlorine → chloroethene… which
interacts with ethanol → PVC
• React with benzene → phenylethene (styrene)…
which interacts with ethanol → polystyrene
• Hydrogenated oils (margarine)
With H2SO4 catalyst
1. Finish 10.3 #9
2. Use labeled drawings (of saturated and
unsaturated hydrocarbons), to explain why
saturated hydrocarbons tend to be solids at
room temperature, while unsaturated
hydrocarbons are usually liquids.