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Chapter 12 Alkenes and Alkynes

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Chapter 12 Alkenes and Alkynes

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    1. Chapter 12 Alkenes and Alkynes

    2. Alkenes and Alkynes Alkene: A hydrocarbon that contains one or more carbon-carbon double bonds. Ethylene is the simplest alkene. Alkyne: A hydrocarbon that contains one or more carbon-carbon triple bonds. Acetylene is the simplest alkyne.

    3. Bonding in Unsaturated Hydrocarbons

    4. Bonding in Unsaturated Hydrocarbons

    5. VSEPR

    6. IUPAC Naming - Alkenes To name an alkene; The parent name is that of the longest chain that contains the C=C (sound familiar?). Number the chain from the end that gives the lower numbers to the carbons of the C=C. Locate the C=C by the number of its first carbon. Use the ending -ene to show the presence of the C=C Branched-chain alkenes are named in a manner similar to alkanes in which substituted groups are located and named.

    7. Common Names

    8. Examples

    9. More than 1 double bond?

    10. Examples

    11. Cis/Trans Cis-trans isomerism Because of restricted rotation about a carbon-carbon double bond, an alkene with two different groups on each carbon of the double bond shows cis-trans isomerism.

    12. EZ system (NIB) Because everything attached to the carbon-carbon double bond is different, there aren't any obvious things which you can think of as being "cis" or "trans" to each other. We need to assign a priority to each group attached to the double bond. Cahn-Ingold-Prelog - You look first at the atoms attached directly to the carbon atoms at each end of the double bond - thinking about the two ends separately. The atom which has the greater atomic number is given the higher priority.

    13. How its done

    14. Examples

    15. Cycloalkenes To name a cycloalkene: Number the carbon atoms of the ring double bond 1 and 2 in the direction that gives the lower number to the substituent encountered first. Note that it is not necessary to explicitly number the position of the double bond in a cycloalkene as in linear alkenes. Number and list substituents in alphabetical order.

    16. IUPAC Naming - Alkynes To name an alkyne; Same as naming alkenes but use yne to denote the presence of a triple CC bond. Book does not go over many reactions or names we will.

    17. Examples

    18. Physical Properties Alkenes and alkynes are nonpolar compounds. The only attractive forces between their molecules are London dispersion forces. Their physical properties are similar to those of alkanes with the same carbon skeletons. Geometry around the double or triple bond is different however. Alkenes and alkynes are insoluble in water but soluble in one another and in nonpolar organic liquids. Alkenes and alkynes that are liquid or solid at room temperature have densities less than 1.0 g/mL; they float on water.

    19. Addition Mechanisms

    21. Hyperconjugation

    23. Can you recognize the following carbocations? 1o, 2o, 3o

    24. Addition of Hydrogen Halides: Markovnikovs rule

    25. Markovnikovs Rule

    28. Mechanisms We will now spend a week or so going over reaction mechanisms and predicting products for a few addition reactions. You will need to take notes as there are no slides for these reactions. Well also discuss carbocation rearrangements and hydrogen shifts.

    29. Why are alkenes and alkynes important? Polymers technology Found in nature Pharmaceuticals

    30. Polymers Movie

    31. Poly(mer)

    32. Biopolymers

    33. Terpenes Terpene: A compound whose carbon skeleton can be divided into five-carbon units identical with the carbon skeleton of isoprene. Terpenes illustrate an important principle of the molecular logic of living systems. In building large molecules, small subunits are bonded together by a series of enzyme-catalyzed reactions and then chemically modified by additional enzyme-catalyzed reactions.

    34. Examples

    35. Sight driven by Cis/Trans Isomerism

    36. End of Chapter 12 Please review the notes on mechanisms. Exam 3 will cover all of chapter 12 naming, mechanisms as well. A large part will be reactions and mechanisms. Understand the basics of polymers we will revisit this later in the year.

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