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Unformatted text preview: 1 Chapter Twelve ALKENE Alkenes Introduction s Unsaturated Unsaturated hydrocarbons hydrocarbons that that contain contain one or more C-C double bonds, triple bonds, or benzenes. b Alkenes: one or more double bonds. (C n H 2n ) b Alkynes: one or more triple bonds. (C n H 2n-2 ) s Thermal Thermal cracking cracking: major process for the production of ethylene. b A saturated hydrocarbon is converted to an unsaturated hydrocarbon. C H 2 CH 2 CH 3 CH 3 + H 2 thermal cracking Alkenes s Structure: b The VSEPR model predicts bond angles of 120 about each carbon of a double bond. b In ethylene, the actual angles are close to 120. b In substituted alkenes, angles about each carbon of the double bond may be greater than 120 because of repulsion between groups bonded to the double bond. H C C H H H 121.7 H 3 C C C H H H 124.7 Ethylene Propene Structures s Alkenes: under normal conditions, no rotation allowed around the carbon-carbon double bond. s Cis-Trans isomerism trans-2-Butene mp -106C, bp 1C cis-2-Butene mp -139C, bp 4C H C C CH 3 H 3 C H H C C H H 3 C CH 3 2 Nomenclature of Alkenes and Alkynes s IUPAC system s Prefix---indicate carbon number in the chain. s Suffix- ene---indicate alkene. s Suffix yne---indicate alkyne. Step 1 Step 1. Find the longest carbon chain that includes double bond (or triple bond). Step 2 Step 2. Number the chain so that double bond has the lower set of number. Designate the position of the double bond by its first C number. Step 3 Step 3. Branched alkenes are named in a manner similar to alkanes....
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This note was uploaded on 12/18/2010 for the course CHEM 10054 taught by Professor Ding during the Spring '10 term at Kent State.
- Spring '10
- Organic chemistry