Alkene Chemistry - Lecture notes 4 PDF

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Alkene Chemistry - Albizati...

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Chapter 11 Alkenes • Alkenes consist of a strong sp3-hybridized sigma bond and a weaker pi bond.

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No rotation on double bonds at normal temps.

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Exist as stable stereoisomers.

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Almost no coupling in geminal

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Trans isomers are usually more stable than the cis isomers

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Physical properties of alkenes • Increasing S character makes carbons increasingly electronegative. • Lower pKa = higher acidity • Alkenes tend to have more S character, which results in higher acidity and lower pKa.

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Suffix -ene • Nomenclature

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E,Z nomenclature • Assign priority: ▪ Z = same side (Zussamen: german for same) ▪ E = opposite side

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Generally, in cycloalkenes 7 or less, only cis double bonds. ▪ 8 or up can be trans Alkene synthesis •

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Treat cyclohexene with strong base can trigger E2 elimination Dehydrohalogenation-E2 elimination where hydrogen and halogen is removed to form alkene

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1/23/17 o Dehydrohalogenation: usually E1 o Alcohol dehydration: usually E2 • Hard to predict carbocations Chapter 12: Reactions of Alkenes • Oxidation: o Increase in # of bonds from C--X (X=O,N,S, Halogen) o And/or decrease in # of C--H bonds

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Reduction o Decrease in # of bonds in covalent bond to an electronegative element. o And/or increase in # of C--H bonds

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Hydrogenation of Alkenes o 3 phases: • Gas, liquid, catalyst o H are added syn, so on same side (cis). o Anti-addition is not observed....