• 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.
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