Lecture Chap11

8/14/2019 Lecture Chap11

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Chapter 11 UnsaturatedHydrocarbons

11.1Alkenes and Alkynes


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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-Cbonds.

CH3CH

2CH

3

Saturated Hydrocarbons


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Unsaturated hydrocarbons have fewer hydrogen

atoms attached to thecarbon chain than alkanes.

are alkenes with doublebonds.

are alkynes with triplebonds.

Unsaturated Hydrocarbons


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Bond Angles in Alkenes andAlkynes

According to VSEPR theory: the three groups bonded to

carbon atoms in a double bond

are at 120 angles. alkenes are flat because theatoms in a double bond all liein the same plane.

the two groups bonded to eachcarbon in a triple bond are at180 angles.


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Naming Alkenes

The names of alkenes use the corresponding alkane name. change the ending to ene.

Alkene IUPAC CommonH2C=CH2 ethene ethylene

H2C=CHCH3 propene propylene

cyclohexene


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Ethene (Ethylene)

Ethene or ethylene is an alkene with the formula C

2H

4.

has two carbon atoms connectedby a double bond.

has two H atoms bonded to eachC atom.

is flat with all the C and H atomsin the same plane.

is used to accelerate the ripeningof fruits.


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Naming Alkynes

The names of alkynes use the corresponding alkane name. change the ending to yne.

Alkyne IUPAC CommonHCCH ethyne acetylene

HCCCH3

propyne


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Naming Alkenes and Alkynes

When the carbon chain of an alkene or alkyne has four or more Catoms, number the chain to give the lowest number to the first carbonin the double or triple bond.

CH2=CHCH2CH3 1-butene

1 2 3 4CH3CH=CHCH3 2-butene

1 2 3 4

CH3CH2C CCH3 2-pentyne

5 4 3 2 1


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Learning Check

Write the IUPAC name for each of the following:

1. CH2=CHCH2CH3

2. CH3CH=CHCH3CH3|

3. CH3CH=CCH3

4. CH3C CCH3


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Solution


1. CH2=CHCH2CH3 1-butene

2. CH3CH=CHCH3 2-butene

CH3|

3. CH3CH=CCH3 2-methyl-2-butene

4. CH3C CCH3 2-butyne


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Learning Check


A. CH3CH2CCCH3

CH3

B. CH3CH2C=CHCH3


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Solution

Write the IUPAC name for each of the following:A. CH

3CH

2CCCH

32-pentyne

CH3

B. CH3CH

2C=CHCH

33-methyl-2-pentene


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11.2Cis-Trans Isomers


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Cis and Trans Isomers

In an alkene the double bond, is rigid. holds attached groups in fixed positions.

makes cis/trans isomers possible.

CH3

CH3

CH3

CH = CH CH = CH

cis trans CH3


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In cis-trans isomers there is no rotation around

the double bond in alkenes.

groups attached to thedouble bond are fixedrelative to each other.

You can make a double

bond with your fingers withboth thumbs on the sameside or opposite from eachother.

Cis-Trans Isomers


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Two isomers are possible whengroups are attached to thedouble bond are different. In a cis isomer, groups are

attached on the same side ofthe double bond.

In thetrans isomer, thegroups are attached onopposite sides.

Cis-Trans Isomers


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Cis-Trans Isomerism

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

Identical Identical

2-bromopropene 1,1-dibromoethene(not cis or trans) (not cis or trans)

C C

H Br

HCH3

C C

H Br

BrH

H

H

HBr


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Cis-Trans Isomers in Nature

Insects emit tiny quantities of pheromones, which arechemicals that send messages.

The silkworm moth attracts other moths by emittingbombykol, which has one cis and one trans doublebond.


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Naming Cis-Trans Isomers

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

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

C C

Br H

BrH

C C

Br Br

H H


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Learning Check

Name each, using cis-transprefixes 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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11.3Addition Reactions


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Addition Reactions

In alkene and alkynes The double or triple

bond is easily broken,which makes doubleand triple bonds veryreactive.

In addition reactions,reactants are added tothe carbon atoms in thedouble or triple bond.


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Inhydrogenation, 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 H

Pt H2H2C CH2 +


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Adding H2 to doublebonds in vegetableoils produces

Compounds withhigher melting points. Solids at room

temperature such asmargarine,

soft margarine,and shortening.

Hydrogenation of Oils


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Learning Check

Write an equation for the hydrogenation of 1-buteneusing a platinum catalyst.


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Solution

Write an equation for the hydrogenation of 1-butene usinga platinum catalyst.

Pt

CH2=CHCH

2CH

3+ H

2CH

3CH

2CH

2CH

3


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Trans Fats

In vegetable oils, the unsaturated fats usually containcis double bonds.

During hydrogenation, some cis double bonds areconverted to trans double bonds (more stable)causing a change in the fatty acid structure.

If a label states partially or fully hydrogenated, the

fats contain trans fatty acids.


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Learning Check

(1) True or (2) False

A. ____ There are more unsaturated fats in vegetable oils.B. ____ Hydrogenation converts some cis-double bonds to

trans- double bonds.C. ____ Animal fats have more unsaturated fats.


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Solution

(1) True or (2) False

A. 1 There are more unsaturated fats in vegetable oils.

B. 1 Hydrogenation of oils converts some cis-doublebonds to trans- double bonds.C. 2 Animal fats have more unsaturated fats.


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Learning Check

Write the product of each the following.

Pt

CH3CH=CHCH3 + H2

Pt

+ H2


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Solution

Pt1. CH

3CH=CHCH

3+ H

2CH

3CH

2CH

2CH

3

2. + H2 Pt


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Hydration

In the addition reaction called hydration, an acid H+ catalyst is required. water (HOH) adds to a double bond.

an H atom bonds to one C in the double bond. an OH bonds to the other C. H OH

H+

CH3CH=CHCH3 + HOH CH3CHCHCH3


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Hydration

When hydration occurs with a double bond that has anunequal number of H atoms, the H atom bonds to the C in the double bond with the

more H. the OH bonds to the C in the double bond with the

fewer H atoms. OH H

H+ CH3CH=CH2 + HOH CH3CHCH2


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Learning Check

Write the product for the hydration of each of thefollowing:

H+

1. CH3CH2CH=CHCH2CH3 + HOHCH3 H+

2. CH3C=CHCH2CH3 + HOH

H+

3. + HOH


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Solution

H OH

1. CH3CH

2CHCHCH

2CH

3

CH3

2. CH

3CCHCH

2CH

3

OH H

OH3.

H

Ch t 11 U t t d


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11.4Polymers of Alkenes


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Polymers

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

starches in food, proteins, and DNA in thebody. also synthetic such as polyethylene and

polystyrene, Teflon, and nylon.

have small repeating units called monomers. can be made from reaction of small alkenes.


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Common Synthetic Polymers


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Polymerization

In polymerization, small repeating units called monomersjoin to form a long chain polymer.

monomer unit repeats

n


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Polymers from Addition Reactions


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More Monomers and Polymers


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Learning Check

What is 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 write aportion of a Teflon polymer using four monomers.


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Solution

F F FC=CF tetrafluoroethene

F F F F F F F F

CCCCCCCC portion of Teflon F F F F F F F F


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Recycling Plastics

Recycling is simplified by using codes on plastic items.

1 PETE Polyethyleneterephtalate

2 HDPE High-density polyethylene3 PV Polyvinyl chloride4 LDPE Low-density polyethylene5 PP Polypropylene

6 PS Polystyrene


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Learning Check

What types of plastic are indicated by the followingcodes?

A.

B.

C.

3

PV

5PP

6PS


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Solution

What types of plastic are indicated by the followingcodes?

A. Polyvinyl chloride

B. Polypropylene

C.Polystyrene

.

3

PV

5PP

6PS

Chapter 11 Unsaturated


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11.5Aromatic 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 three double bonds.

represented by two structures because the electronsare shared among all the C atoms.

Aromatic Compounds

Copyright 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings


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Benzene has 6 electrons shared equally among the 6 C atoms. is also represented as a hexagon with a circle drawn

inside.

Benzene Structure

Aromatic Compounds in Nature and


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Aromatic Compounds in Nature andHealth

Vanillin Aspirin

Ibuprofen Acetaminophen

COH

O

O

C O CH3

CH

O

OCH3

OH

CH

CH3

COH

O

CH2

CH3

CHH3

C

OH

NH

O

C CH3


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Naming Aromatic Compounds

Aromatic compounds are named with benzeneas the parent chain. with one side group named in front ofbenzene.

methylbenzene chlorobenzene

ClCH3


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Some Common Names

Some substituted benzene rings have common names that have been in use for many years. with a single substituent use a common name or are named as a

benzene derivative.

toluene aniline phenol

(methylbenzene) (benzenamine) (hydroxybenzene)

NH2 OHCH3


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Naming Aromatic Compounds

When two groups are attached to benzene ring, the ring isnumbered to give the lowest numbers to the side groups.

3-chlorotoluene 1,4-dichlorobenzene 2-chlorophenol

OHCH3

Cl

Cl

Cl

Cl


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Learning Check

Select the correct name for each compound.1) chlorocyclohexane2) chlorobenzene3) 1-chlorobenzene

1) 1,2-dimethylbenzene2) 1,4-dimethylbenzene3) 1,3-dimethylbenzene

CH3

CH3

Cl


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Solution

Select the correct name for each compound.

2) chlorobenzene

3) 1,3-dimethylbenzeneCH3

CH3

Cl


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Learning Check

Write the structural formulas for each of the following.A. 1,3-dichlorobenzene

B. 2-chlorotoluene


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Solution

Write the structural formulas for each of the following.A. 1,3-dichlorobenzene

B. 2-chlorotoluene

Cl

Cl

CH3

Cl


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Learning Check

Identify the organic family for each:

A. CH3CH

2CH=CH

2

B.

C. CH3CCH

D.


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Solution

Identify the organic family for each:

A. CH3CH

2CH=CH

2alkene

B. cycloalkane (alkane)

C. CH3CCH alkyne

D. aromatic

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