Chapter 13 Unsaturated Hydrocarbonsdfard.weebly.com/uploads/1/0/5/3/10533150/ch13_cas.pdf · Two...

1Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.

Alkenes and AlkynesNaming Alkenes and AlkynesCis-Trans Isomers

Chapter 13 Unsaturated Hydrocarbons


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


Unsaturated hydrocarbons: Have fewer hydrogen atoms attached to the carbon chain than alkanes.Are alkenes with double bonds or alkynes with triple bonds.

13.1Unsaturated Hydrocarbons


Alkenes Have Double BondsIn a double bond:

One pair of electrons form a strong sigma (σ) bond.One pair of electrons in adjacent p orbitalsoverlap to form a pi (π) bond.


Alkynes have Triple Bonds

In a triple bond: One pair of electrons form a strong sigma (σ) bond.Two pairs of electrons in adjacent p orbitals overlap to form two pi (π) bonds.


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°.


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

Naming Alkenes and Alkynes


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.1 CH2=CH—CH2—CH3 1-butene

2CH3—CH=CH—CH2—CH3 2-pentene

3CH3—CH2—C≡C—CH2—CH3 3 -hexyne

13.2Naming Alkenes and Alkynes


Write the IUPAC name for each:A. CH3—CH2—C≡C—CH3

CH3|

B. CH3—C=CH—CH3 C. CH3

Learning Check


Write the IUPAC name for each:A. CH3—CH2—C≡C—CH3

2-pentyne

CH3|

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

CH3

Solution


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.

13.3Cis-Trans Isomers


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


Cis-Trans Isomers in NatureInsects 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.


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

BrHC C

Br Br

H H


Cis-Trans IsomerismAlkenes 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


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.


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.


13.6 Addition Reactions



Addition ReactionsThe pi (π) bond is easily broken, which makes double and triple bonds very reactive.In the additionreaction, reactants are added to the carbon atoms in the double or triple bond.


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 + 2H2

NiHC CH

H H

H H

H2C CH2

H HPt

H2H2C CH2 +


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

Hydrogenation of Oils


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

Learning Check


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

NiCH2=CH—CH2—CH3 + H2

CH3—CH2—CH2—CH3

Solution


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 +


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.


Write the product of each addition reaction:

PtCH2=CH—CH3 + H2

+ Br2

Learning Check


Write the product of each addition reaction:

PtCH2=CH—CH3 + H2 CH3—CH2—CH3

Solution

Br

Br

+ Br2


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


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.

CH3 CH CH2

Cl H

Markovnikov’s Rule

CH3 CH CH2 + HCl

CH3 CH CH2

H Cl

Does not form

C with the most H

Product that forms


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+


Learning CheckWrite the products of each reaction.

+ H2

CH3 CH CH2 + Cl2

Pt

H+

CH3 CH CH CH3 + HOH

A.

B.

C.


SolutionWrite 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


13.8 Polymerization



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.


Common Synthetic Polymers


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

Repeating monomer

chain continues chain continues

Polyethylene

Ethylene monomers

C C C C C C

H H

HH

H

H

H

H

H

H

H

H

++ C C

H H

HH

C C

H H

HH

C C

H H

HH


Polymers from Addition Reactions


More Monomers and Polymers


Recycling PlasticsRecycling is simplified by using codes on plastic items.

1 PETE Polyethyleneterephtalate2 HDPE High-density polyethylene3 PV Polyvinyl chloride4 LDPE Low-density

polyethylene5 PP Polypropylene6 PS Polystyrene


Learning CheckWhat 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


SolutionWhat 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



13.9 Aromatic Compounds


Benzene isAn 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.

Aromatic Compounds


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.

13.9Benzene Structure


Aromatic Compounds in Nature and Medicine


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

Methylbenzene Chlorobenzene

13.10Naming Aromatic Compounds

ClCH3


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)


A benzene ring with two or more substituentsis 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-).

Br

Br

Naming Aromatic Compounds

Cl

Cl

CH3

Cl

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


Select the correct name for each structure:

1) chlorocyclohexane2) chlorobenzene3) 1-chlorobenzene

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

Cl

Learning Check

Cl

Cl


Select the correct name for each structure:

2) Chlorobenzene

1) 1,3-dichlorobenzene

3) m-dichlorobenzene

Cl

Solution

Cl

Cl


Write the structural formula for each:A. 1-bromo-4-chlorobenzene

B. o-chlorotoluene

Learning Check


Write the structural formula for each:

A. 1-bromo-4-chlorobenzene

B. o-chlorotolueneCH3

Cl

Solution

Cl

Br



13.11 Properties of Aromatic Compounds

ChlorobenzeneBenzene

FeCl3 HCl+

Cl

Cl2+

H


Properties 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.


Substitution ReactionsIn 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


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.

ChlorobenzeneBenzene

FeCl3 HCl+

Cl

Cl2+

H


Nitration

Nitration replaces a H on benzene by a nitro (—NO2) group from HNO3. An acid catalyst such as H2SO4 is used in nitration.

NitrobenzeneBenzene

H2SO4 HOH+

NO2

HNO3+

H


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


Learning Check

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


Solution

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

HBr+

FeBr3

Br

Br2+

H

Chapter 13 Unsaturated Hydrocarbonsdfard.weebly.com/uploads/1/0/5/3/10533150/ch13_cas.pdf · Two...

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