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Unformatted text preview: 2. Name the fo llowing compound: 3. Is the compound shown below cis or trans iso mer? Name this co mpound. H C
3 CH 3 C H C H C 2 CH 3 4. Draw structure for cis5chloro2hexene. 4 C H 3
C H 3 Chemistry 52 Chapter 20 DIENES & TRIENES:
· Many co mpounds have more than one C=C. Compounds with two C=C are called dienes, and are named by numbering each carbon bearing the double bond.
H C CH 2
C H H C 2 1,3butadiene · Compounds with three double bonds are called trienes and are named similar to other alkenes. Examples: 1. Name the diene shown below, one of the components of natural rubber. 5 Chemistry 52 Chapter 20 PREPARATION OF ALKENES
· Alkenes can be prepared by one of two methods: 1. Cracking of alkanes 2. Dehydrat ion of alcoho ls · Cracking, or pyrolysis, is the process in which saturated hydrocarbons are heated to very high temperatures in the presence of a catalyst (usually silicaalumina): Alkane (CnH2n+2) ® Mixture of alkenes + Alkanes + H2 (g) 2 CH3CH2CH3 ® CH3CH=CH2 + CH2=CH2 + CH4 + H2 · Dehydrat ion invo lves the eliminat ion of a mo lecule of water fro m a reactant mo lecule. H H C C H H C C conc. H SO 2 4 H C 3 CH 3 heat H H C 3 CH 3 + H O 2 O H · These react ions will be further discussed in Chapter 22. Examples: Predict and name the alkene formed fro m dehydratio n of each alcoho l shown below: 1) O H H C 3 2) H 2 SO 4 CH 3 OH Heat H SO 2
Hea t 6 Chemistry 52 Chapter 20 REACTIONS OF ALKENES
· Alkenes can undergo addition react ions...
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