Unsaturated Hydrocarbons Double and Triple bonds between Carbons.
Ch. 11: Unsaturated Hydrocarbons
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Transcript of Ch. 11: Unsaturated Hydrocarbons
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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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