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Chapter 13

Alkanes, Alkynes, and Aromatic Compounds

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Saturated hydrocarbons: Have the maximum number of hydrogen

atoms attached to each carbon atom. Are alkanes and cycloalkanes with single

C-C bonds.

CH3—CH2—CH3

Saturated Hydrocarbons

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Unsaturated hydrocarbons:

Have fewer hydrogen atoms attached to the carbon chain than alkanes.

Are alkenes with double bonds or alkynes with triple bonds.

13.1 Alkenes and Alkynes

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Alkenes Have Double Bonds

In a double bond: One pair of electrons

form a strong sigma () bond.

One pair of electrons in adjacent p orbitals overlap to form a pi () bond.

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Alkynes have Triple Bonds

In a triple bond: One pair of electrons

form a strong sigma () bond.

Two pairs of electrons in adjacent p orbitals overlap to form two pi () bonds.

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Bond Angles in Alkenes and Alkynes

According to VSEPR theory:

The three groups bonded to carbon atoms in a double bond are at angles of 120°.

The two groups bonded to each carbon in a triple bond are at angles of 180°.

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In the IUPAC system, the –ane ending of the corresponding alkane is changed to –ene for alkenes and to –yne for alkynes.

13.2 Naming Alkenes and Alkynes

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When the carbon chain has 4 or more C atoms, the chain is numbered to give the lowest number to the double or triple bond.

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CH2=CH—CH2—CH3 1-butene 2

CH3—CH=CH—CH2—CH3 2-pentene 3

CH3—CH2—CC—CH2—CH3 3 -hexyne

Naming Alkenes and Alkynes

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Write the IUPAC name for each:

A. CH3—CH2—CC—CH3

CH3

|B. CH3—C=CH—CH3 C.

Learning Check

CH3

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Write the IUPAC name for each:

A. CH3—CH2—CC—CH3

2-pentyne

CH3

|B. CH3—C=CH—CH3 C. 2-methyl-2-butene 3-methylcyclopentene

Solution

CH3

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There is no rotation around the double bond in alkenes.

Groups attached to the double bond are fixed relative to each other.

You can make a “double bond” with your fingers with both thumbs on the same side or opposite from each other.

13.3 The Structure of Alkenes: Cis-Trans Isomerism

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Two isomers are possible when groups are attached to the double bond.

In a cis isomer, groups are attached on the same side of the double bond.

In the trans isomer, the groups are attached on opposite sides.

Cis-Trans Isomers

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Cis-Trans Isomers in Nature Insects emit tiny quantities of pheromones, which

are chemicals that send messages. The silkworm moth attracts other moths by

emitting bombykol, which has one cis and one trans double bond.

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Naming Cis-Trans Isomers

The prefixes cis or trans are placed in front of the alkene name when there are cis-trans isomers.

cis-1,2-dibromoethene trans-1,2-dibromoethene

C C

Br H

BrH

C C

Br Br

H H

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Cis-Trans Isomerism

Alkenes cannot have cis-trans isomers if a carbon atom in the double bond is attached to identical groups.

Identical Identical

2-bromopropene 1,1-dibromoethene

C C

H Br

H CH3

C C

H Br

BrH

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Learning Check

Name each, using cis-trans prefixes when needed.

C C

CH3 H

CH3H

C C

Br Br

H H

A.

B.

C C

CH3 Cl

ClH

C.

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Solution

cis-1,2-dibromoethene

trans-2-butene

1,1-dichloropropene

C C

CH3 H

CH3H

C C

Br Br

H H

A.

B.

C C

CH3 Cl

ClH

C.

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13.4 Addition Reactions

13.4 Properties of Alkenes and Alkynes

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Addition Reactions The pi () bond is

easily broken, which makes double and triple bonds very reactive.

In the addition reaction, reactants are added to the carbon atoms in the double or triple bond.

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In hydrogenation, hydrogen atoms add to the carbon atoms of a double bond or triple bond.

A catalyst such as Pt or Ni is used to speed up the reaction.

Hydrogenation

HC CH + 2H2Ni

HC CH

H H

H H

H2C CH2

H HPt

H2H2C CH2 +

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When hydrogen adds to the double bonds in vegetable oils, the products are solids at room temperature.

Hydrogenation of Oils

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Write the equation for the addition of hydrogen to 1-butene using a Ni catalyst.

Learning Check

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Write the equation for the addition of hydrogen to 1-butene using a Ni catalyst.

Ni

CH2=CH—CH2—CH3 + H2

CH3—CH2—CH2—CH3

Solution

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In halogenation, halogen atoms add to the carbon atoms of a double bond or triple bond.

Halogenation

+ HC C CH3 2Cl2 C C

Cl Cl

Cl Cl

CH3H

H2C CH2

Br Br

Br2H2C CH2 +

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Testing for Double and Triple Bonds

When bromine (Br2) is added to an alkane, the red color of bromine persists.

When bromine (Br2) is added to an alkene or alkyne, the red color of bromine disappears immediately.

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Write the product of each addition reaction:

Pt CH2=CH—CH3 + H2

+ Br2

Learning Check

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Write the product of each addition reaction:

Pt CH2=CH—CH3 + H2 CH3—CH2—CH3

Solution

Br

Br

+ Br2

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In hydrohalogenation, the atoms of a hydrogen halide add to the carbon atoms of a double bond or triple bond.

Hydrohalogenation

CH3 CH CH CH3

H Cl

+ HClCH3 CH CH CH3

H

Br

+ HBr

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When an unsymmetrical alkene undergoes hydrohalogenation, the H in HX adds to the carbon in the double bond that has the greater number of H.

Markovnikov’s Rule

CH3 CH CH2

Cl H

CH3 CH CH2 + HCl

CH3 CH CH2

H Cl

Does not form

C with the most H

Product that forms

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In hydration, H and OH from water add to the carbon atoms of a double bond or triple bond to form alcohols (OH).

The reaction is catalyzed by acid H+.

Hydration Adds Water

+ HOHH

OH

CH3 CH CH2 + HOH

CH3 CH CH2

OH H

H+

H+

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Learning Check

Write the products of each reaction.

+ H2

CH3 CH CH2 + Cl2

Pt

H+

CH3 CH CH CH3 + HOH

A.

B.

C.

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Solution

Write the products of each reaction.

CH3 CH CH CH3

H OH

C.

B.

A.

HOH +CH3 CH CH CH3

H+

Pt

CH3 CH CH2

Cl Cl

+ Cl2 CH3 CH CH2

H

H

+ H2

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13.8 Alkene Polymers

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Polymers

Polymers are: Long-chain molecules. Found in nature, including cellulose in

plants, starches in food, proteins and DNA in the body.

Also synthetic such as polyethylene and polystyrene, Teflon, and nylon.

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Common Synthetic Polymers

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Polymerization

In polymerization, small repeating units called monomers are bonded to form a long chain polymer.

Repeating monomer

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Recycling Plastics Recycling is simplified by using

codes on plastic items.

1 PETE Polyethyleneterephtalate

2 HDPE High-density polyethylene

3 PV Polyvinyl chloride

4 LDPE Low-density polyethylene

5 PP Polypropylene

6 PS Polystyrene

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Learning Check

What is the starting monomer for polyvinyl chloride (PVC)?

C C C C C C

H Cl

HH

H

H

Cl

H

H

H

Cl

H

Polyvinyl chloride

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Solution

What is the starting monomer for polyvinyl chloride (PVC)?

Chloroethene monomers

++ C C

H Cl

HH

C C

H Cl

HH

C C

H Cl

HH

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Chapter 13 Unsaturated Hydrocarbons

13.6 Aromatic Compounds

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Benzene is An aromatic compound.

A ring of 6 C atoms and 6 H atoms. A flat ring structure drawn with double bonds. Represented by two structures because the electrons

move among the C atoms.

13.9 Aromatic Compounds and the Structure of Benzene

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Because the pi electrons in benzene are shared equally among the 6 C atoms, benzene can also be represented as a hexagon with a circle drawn inside.

Benzene Structure

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Aromatic Compounds in Nature and Medicine

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A benzene with a single substituent is often named as a benzene derivative.

Methylbenzene Chlorobenzene

13.10 Naming Aromatic Compounds

ClCH3

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Some substituted benzene rings have common names that have been in use for many years.

Some Common Names

CH3 NH2 OH

Toluene Aniline Phenol(Methylbenzene) (Benzenamine) (Hydroxybenzene)

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A benzene ring with two or more substituents is numbered to give the lowest numbers to the side groups.

Common names use the prefixes ortho- (1,2-), meta- (1,3-) and para- (1,4-).

Naming Aromatic Compounds

Br

Br

Cl

Cl

CH3

Cl

1,2-dimethylbenzene 1,3-dichlorobenzene 4-chloromethylbenzene(o-dibromobenzene) (m-dichlorobenzene) (p-chlorotoluene)

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Select the correct name for each structure:

1) chlorocyclohexane2) chlorobenzene3) 1-chlorobenzene

1) 1,3-dichlorobenzene2) o-dichlorobenzene3) m-dichlorobenzene

Learning Check

Cl

Cl

Cl

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Select the correct name for each structure:

2) Chlorobenzene

1) 1,3-dichlorobenzene

3) m-dichlorobenzene

Solution

Cl

Cl

Cl

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Write the structural formula for each:

A. 1-bromo-4-chlorobenzene

B. o-chlorotoluene

Learning Check

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Write the structural formula for each:

A. 1-bromo-4-chlorobenzene

B. o-chlorotoluene

Solution

CH3

Cl

Cl

Br

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Chapter 13 Unsaturated Hydrocarbons

13.7 Properties of Aromatic Compounds

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13.11 Reactions of Aromatic Compounds

Aromatic compounds: Have a stable aromatic bonding system. Are resistant to many reactions. Undergo substitution reactions, which

retains the stability of the aromatic bonding system.

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Substitution Reactions

In a substitution reaction, a hydrogen atom on a benzene ring is replaced by an atom or group of atoms.

Type of substitution H on benzene replaced by

Halogenation chlorine or bromine atom

Nitration nitro group (—NO2)

Sulfonation —SO3H group

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Halogenation

Halogenation replaces a H on benzene by a chlorine or bromine atom.

A catalyst such as FeCl3 is used in chlorination; FeBr3 in bromination.

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Nitration

Nitration replaces a H on benzene by a nitro (—NO2) group from HNO3.

An acid catalyst such as H2SO4 is used in nitration.

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Sulfonation

Sulfonation replaces a H on benzene by a

—SO3H group from SO3.

An acid catalyst such as H2SO4 is used in sulfonation.

Benzenesulfonic acidBenzene

H2SO4

SO3H

SO3+

H

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Learning Check

Write the equation for the bromination of benzene, including catalyst.

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Solution

Write the equation for the bromination of benzene, including catalyst.

HBr+

FeBr3

Br

Br2+

H

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Chapter Summary Alkenes contain carbon-carbon double bonds. Alkynes contain carbon-carbon triple bonds. Aromatic compounds contain six carbons in a ring

arrangement with three double and three single bonds alternating between carbon atoms.

Alkenes are named using the family ending –ene, while the alkynes use the family ending –yne.

Alkenes and alkynes generally undergo addition reactions and aromatic compounds generally undergo substitution reactions.

Reaction mechanism: A description of the individual steps by which old bonds are broken and new bonds are formed.

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End of Chapter 13

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Thank you Thanks so much for a wonderful semester.

You have been so wonderfully Kind to me. I love you so much and will miss you.

Love Divan