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Chapter 3 Alkenes and Alkynes. Unsaturated Hydrocarbons Contain carbon-carbon multiple bonds. Alkenes C=C double bonds Alkynes C≡C triple bonds Aromatics.

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Presentation on theme: "Chapter 3 Alkenes and Alkynes. Unsaturated Hydrocarbons Contain carbon-carbon multiple bonds. Alkenes C=C double bonds Alkynes C≡C triple bonds Aromatics."— Presentation transcript:

1 Chapter 3 Alkenes and Alkynes

2 Unsaturated Hydrocarbons Contain carbon-carbon multiple bonds. Alkenes C=C double bonds Alkynes C≡C triple bonds Aromatics benzene rings

3 © 2006 Thomson Learning, Inc. All rights reserved Alkenes Structure: The VSEPR model predicts bond angles of 120° about each carbon of a double bond.

4 © 2006 Thomson Learning, Inc. All rights reserved Alkenes 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. CIS TRANS

5 © 2006 Thomson Learning, Inc. All rights reserved Problem 43, p. 355 (c) (d)

6 © 2006 Thomson Learning, Inc. All rights reserved Naming Alkenes Step 1: Name the longest chain that contains the C=C bond. Use the IUPAC root and the –ene ending. Step 2: Number the longest chain so the C=C bond gets the lowest number possible. Step 3: Designate the C=C bond in the name with the lowest-numbered carbon.

7 © 2006 Thomson Learning, Inc. All rights reserved Examples: CH 3 -CH=CH-CH 3 2-butene CH 3 -CH 2 -CH 2 -CH=CH-CH 3 2-hexene

8 © 2006 Thomson Learning, Inc. All rights reserved Naming Alkenes, cont. Step 4: Locate and name attached groups. Step 5: Combine all the names as you did with alkanes.

9 © 2006 Thomson Learning, Inc. All rights reserved Alkynes - IUPAC Names ynefollow the same rules as for alkenes, but use the ending -yne to show the presence of the triple bond.

10 Example 12-1, p. 333 (d)

11 © 2006 Thomson Learning, Inc. All rights reserved 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. number and list substituents in alphabetical order.

12 © 2006 Thomson Learning, Inc. All rights reserved Example 12-3, p. 336

13 © 2006 Thomson Learning, Inc. All rights reserved 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. Alkenes and alkynes are insoluble in water but soluble in one another and in nonpolar organic liquids.

14 © 2006 Thomson Learning, Inc. All rights reserved Alkene Reactions Alkenes are quite chemically reactive Many reactions are addition reactions:

15 © 2006 Thomson Learning, Inc. All rights reserved Reactions of Alkenes The most common reaction is addition halogenation hydrohalogenation

16 Alkene Reactions, cont. Hydrogenation (addition) reactions can occur in the presence of a catalyst (Pt, Pd, or Ni). The hydrogenation of vegetable oils is an important commercial process.

17 © 2006 Thomson Learning, Inc. All rights reserved Addition of H 2 Virtually all alkenes add H 2 in the presence of a transition metal catalyst, commonly Pd, Pt, or Ni.

18 © 2006 Thomson Learning, Inc. All rights reserved Addition of a Halogen (Halogenation) Addition takes place readily at room temp. reaction is generally carried out using pure reagents, or mixing them in a nonreactive organic solvent addition of Br 2 is a useful qualitative test for the presence of a carbon-carbon double bond

19 © 2006 Thomson Learning, Inc. All rights reserved Addition of HX (Hydrohalogenation) Addition of HX (HCl, HBr, or HI) to an alkene H adds to one carbon of the C=C and X to the other. Markovnikov’s rule:Markovnikov’s rule: H adds to the less substituted carbon and X to the more substituted carbon.

20 © 2006 Thomson Learning, Inc. All rights reserved Hydration-addition of waterHydration-addition of water

21 © 2006 Thomson Learning, Inc. All rights reserved Addition of H 2 O Hydration follows Markovnikov’s rule; H adds to the less substituted carbon and OH adds to the more substituted carbon.

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23 Polymerization Polymers – long chain products made up of repeating units. Monomer – the starting material that becomes the repeating units of a polymer.

24 Table 12-2, p. 349

25 © 2006 Thomson Learning, Inc. All rights reserved Polymerization Show the structure of a polymer by placing parentheses around the repeating monomer unit. Place a subscript, n, outside the parentheses to indicate that this unit repeats n times. The structure of a polymer chain can be reproduced by repeating the enclosed structure in both directions. following a section of polypropene (polypropylene)


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