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Chapter 17 Organic Chemistry

17.2 Alkenes, Alkynes, and Polymers

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Unsaturated Compounds: Alkenes and AlkynesUnsaturated compounds • have fewer hydrogen

atoms attached to the carbon chain than alkanes

• are alkenes with C=C double bonds

• are alkynes with triple C≡C bonds

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Naming Alkenes and Alkynes

The names of alkenes and alkynes• use the corresponding alkane names • change the end to ene for alkenes

• change the end to yne for alkynes

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Naming Alkenes and Alkynes

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Naming Alkenes and Alkynes

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Example of Writing an Alkene Name Write the IUPAC name for the following:

CH3

| CH3─CH=C─CH3

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Example of Writing an Alkene Name (continued)STEP 1 Name the longest carbon chain that

contains a double or triple bond.

butene

STEP 2 Number the carbon chain starting from the end nearer the double or triple bond.

CH3

| CH3─CH=C─CH3

4 3 2 1

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Example of Writing an Alkene Name (continued)STEP 3 Give the location and name of each

substituent (alphabetical order) as a prefix to the alkene or alkyne name.

CH3

|CH3─CH=C─CH3 2-methyl-2-butene

4 3 2 1

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Learning Check

Write the IUPAC name for the following: Br

CH3─CH─CC─CH3

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Solution

STEP 1 Name the longest carbon chain that contains a double or triple bond.

pentyne

STEP 2 Number the carbon chain starting from the end nearer the double or triple bond.

Br

CH3─CH─C≡C─CH3 5 4 3 2 1

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Solution (continued)

STEP 3 Give the location and name of each substituent (alphabetical order) as a prefix to the alkene or alkyne name.

Br

CH3─CH─C≡C─CH3 5 4 3 2 1

4-bromo-2-pentyne

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Learning Check

Draw the condensed structural formula for

2-methyl-3-hexyne.

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Solution

STEP 1 Draw the main chain of carbon atoms. For 3-hexyne, there are six carbon atoms in the chain, with

a triple bond between carbons 3 and 4,C─C─C≡C─C─C

STEP 2 Number the chain and place the substituents on the carbons indicated by the numbers.

CH3 C─C─C≡C─C─C

1 2 3 4 5 6

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Solution (continued)

STEP 3 Add the correct number of hydrogen atoms to give four bonds to each C atom.

CH3

CH3─CH─C≡C─CH2─CH3

1 2 3 4 5 6

2-methyl-3-hexyne

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Polymers

Polymers are • large, long-chain molecules• found in nature, including cellulose in plants,

starches in food, and proteins and DNA in the body

• also made synthetically, for example, polyethylene and polystyrene, Teflon, and nylon

• made up of small repeating units called monomers

• made by reaction of small alkenes

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Synthetic Polymers in Everyday Items

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PolymerizationIn polymerization, small repeating units called

monomers join to form a long-chain polymer.

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Some Alkenes and Their Polymers

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Learning Check

What is the name and condensed structural formula of the starting monomer for polyethylene?

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Solution

Ethene (ethylene)

CH2=CH2

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Learning Check

Name the monomer used to make Teflon, and use four monomers to draw the condensed structural formula of a portion of a Teflon polymer.

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Solution

F F │ │ F─C═C─F tetrafluoroethene (monomer)

F F F F F F F F │ │ │ │ │ │ │ │ ─C─C─C─C─C─C─C─C─ portion of Teflon │ │ │ │ │ │ │ │ F F F F F F F F

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Recycling Plastics

Recycling is simplified by using codes found on plastic items.

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Learning Check

What type of plastic is indicated by each of the following codes?

A.

B.

C.

3 PVC

5PP

6PS

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Solution

A. Polyvinyl chloride

B. Polypropylene

C. Polystyrene

5PP

6PS

3 PVC