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Ch. 11: Unsaturated Hydrocarbons

Chem 20

El Camino College

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Unsaturated Hydrocarbons

Unsaturated means that the molecule contains one or more multiple bonds

Alkenes contain a double bond Alkynes contain a triple bond

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Label as alkane, alkene, or alkyne

H3C C C CH3

alkanealkenealkynealkene

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Naming Name the longest carbon chain that contains

the multiple bond (-ene or –yne) Number the chain to give the multiple bond

the lowest number, show location Give the location and name of each

substituent in alphabetical order, using numbers, hyphens, and commas between numbers

Give location of the double bond (if needed)

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Name These

H3C C C CH3H2C

HC

CH2

CH3

propene

1-butene

2-butene

2-butyne

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Name These

2-methylpropene

3-bromo-3-chloro-1-butene

4,4-dibromo-1-butyne

HC C CH2

CHH2C

HC

C

CH3

Br ClBr

Br

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Draw These

1-chloro-1,2,2-trifluoroethene

1,2-dimethyl-1-cyclohexene

1,1,4,4-tetrabromo-2-pentyne

F

C

C

F

F

Cl

C

C

CH3

CH3

H

H

H

HH H

H H

C C CH

H3C

BrBr Br

Br

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Cis-Trans Isomers

cis--on the same side of the double bond trans--on opposite sides of the double bond

The cis and trans isomers are different molecules and have different properties

cis-2-butene bp = 3.7 oC trans-2-butene bp = 0.3 oC

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Cis-Trans Isomers

The groups that are cis and trans may differ cis & trans do not refer to gps on the same C The words cis and trans come first in the names,

followed by a hyphen

F

H Br

H F

H H

Br

trans-1-bromo-2-fluoroethene cis-1-bromo-2-fluoroethene

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Write the names

Cl

HH

Br

1-pentene

4-chloro-1-pentene

trans-3-heptene

cis-1-bromo-1-butene

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Write the names

cis-3,4-dibromo-3-hexene

trans-3,4-dibromo-3-hexene

trans-4,4,6,6-tetrabromo-2-hexene

Br

Br

Br Br

C C

Br

H3CH2C CH2CH3

Br

C C

Br

H3CH2C Br

CH2CH3

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Addition Reactions In addition reactions of alkenes, the double bond

breaks and two atoms add to the molecule

C C + A B C C

BA

We’ll study some addition reactionsAddition of H2 (hydrogenation)

Addition of X2 (halogenation)

Addition of H2O (hydration)

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Hydrogenation In hydrogenation reactions of alkenes, the double bond breaks & 2 H atoms add A catalyst such as Pt, Ni, or Pd speeds up the reactions A cmpd with a multiple bond is unsaturated A cmpd with single bonds only is saturated

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Hydrogenation

C C + H H C C

HH

Ni

Double bonds react with 1 molecule of H2

Triple bonds react with 2 molecules of H2

C C + 2 H H C C

HH

H H

Pd

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Write Product, Name Reactant & Product

+ H HPt

trans-4-methyl-2-pentene 2-methylpentane

+ H HPd

cyclopentene cyclopentane

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Halogenation

Addition of bromine is useful for detection of carbon-carbon double bond

Double bond reacts with 1 molecule of bromine

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Bromination

Rapid decolorization of a bromine solution is characteristic of compound containing carbon-carbon double bond

One cyclohexene molecule reacts with 1 molecule of bromine to give 1,2-dibromo cyclohexane

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Hydration In hydration reaction of alkene, the double bond breaks, H and OH add with formation of an alcohol An acid catalyst (shown as H+) is used If the two “C”s of the double bond are attached to different groups, H adds to the carbon of the

double bond with more “H”s.

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Hydration

C C

H

H H

H

H OH H C C H

OHH

H H

H+

C C

H3C

H3C H

H

H OH H3C C C H

HOH

CH3 H

H+

side with more "H"s

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Write Product, Name Reactant,

2-methyl-2-butene

C5H12O

cyclohexene

C6H12O+ H OHH+

OH

+ H OHH+

OH

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3-D (Spatial) Drawings

Bonds lying on the plane of the paper are shown with ordinary lines

Bonds coming out of the page are shown as solid wedges

Bonds going to the back of the page are shown as dashed (striped, broken)wedges

H

C

HH

H

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3-D (Spatial) Drawings

Note--every tetrahedral will have two lines, one broken wedge(dash), and one solid wedge. The lines make the zig-zag chain.

H3C CH2 OH is the same as

H3C

CH2

O

His the same as H

C

C

O

H

H

HH

H

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3-D (Spatial) Drawings

Draw a spatial drawing for butane

H

C

C

C

C

H

HH

H

H

H H

HH

Draw a spatial drawing for 2,2-dibromopropane

H

C

C

C

H

BrBr

H H H

H

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3-D (Spatial) Drawings Do not show planar atoms with dashes or wedges

Draw a spatial drawing for trans-1-bromo-1-propene

H

C

C

C

H H

H

H

H H

H

C C HH

H

H

ethene ethyne 1-propene

C C

Br

H C

H

H H

H

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Aromatic Hydrocarbon Benzene molecule, C6 H6 , consists of a ring of six carbon atoms with one hydrogen atom

attached to each carbon. Each carbon atom uses three valence electrons to bond to hydrogen atom and two adjacent C

atoms

Six electrons are shared equally among six carbon atoms

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Naming of Aromatic Hydrocarbon

When benzene has only one substituent the benzene ring is not numbered. Example Chlorobenzene

When there are 2 or more substituents the benzene ring is numbered to give the lower numbers to the substituents.

Example 1,3-dichlorobenzene

Common name of Aromatic Compounds

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Naming of Aromatic Hydrocarbon

When a common name such as toluene, phenol or aniline is used, the carbon atom attached to the methyl, hydroxyl, or amine group is number as carbon 1

Example: 2-chlorotoluene

Example: 4-ethyltoluene

Polycyclic Aromatic Compounds (PAHs)

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Polymer

Polymer are large molecules that consist of small units called monomers

Many are made by addition reaction of alkenes. Examples:

Polyethylene monomer is ethylene Polyvinyl chloride monomer is vinyl chloride

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