2.7 Physical Properties of
Alkenes
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•
•
•
•
Nonpolar
Insoluble in water
Soluble in nonpolar organic solvents.
Less dense than water: they float on water.
PHYSICAL PROPERTIES LIKE ALKANES
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2.8 Chemical Properties of
Alkenes
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REACTIONS OF ALKENES
Combustion
Addition reactions :
hydrogenation
halogenation
hydrohalogenation
hydration (addition of water)
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• Addition reactions: A substance adds to
the multiple bond of an unsaturated
reactant to yield a saturated product that
has only single bonds.
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In an addition reaction the atoms of the reactant
molecule attach to the carbon atoms originally
joined by a double bond. The double bond
becomes a single bond.
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1. Symmetrical Addition Reactions: In
which identical atoms are added to each
carbon of the double bond.
2. Unsymmetrical Addition Reactions: In
which different groups are added to each
carbon of the double bond. For example,
hydration or hydrohalogenation.
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1. Symmetrical addition reactions
HYDROGENATION: The addition of H-H to C=C
HALOGENATION: The addition of Cl2 or Br2 to C=C
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HYDROGENATION
C
+
C
H
H
catalyst
catalyst = Pt, Pd, Ni
C
C
H
H
Hydrogenation is the addition of hydrogen (H2) to a
functional group. It requires a catalyst (cat)
+
H2
Pd
H3C
CH3
+
H
Pt
H2
CH3CH2CH2CH3
H
NO REACTION WITH C=C IN AROMATIC RINGS!
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HALOGENATION
Addition of Cl2 and Br2 to alkenes:
• Alkenes react with the halogens Br2 and
Cl2 to give the 1,2-dihaloalkanes.
D:\Chem 11\movies\addition.mov
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Bromine in water
is a reddish
brown solution.
Br2
Bromine adds to the
alkene to form
colorless dibromo
compounds.
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2. UnSymmetrical addition reactions
HYDROHALOGENATION : The addition of H-Cl, HBr or H-I to C=C
Hydration: The addition of H2O to C=C
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HYDROHALOGENATION
Addition of HCl and HBr to alkenes:
• Alkenes react with hydrogen bromide and
hydrogen chloride to give alkyl bromide or
alkyl chloride products.
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•Markovnikov rule: In the addition of HX to an
alkene, the H becomes attached to the carbon that
already has the more H’s, and X becomes
attached to the carbon that has fewer H’s.
D:\Chem
11\movies\HCLadddition.mov
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HYDRATION
Addition of water (H-OH) to alkenes
An alcohol is produced on treatment of
the alkene with water in the presence of a
strong acid catalyst, such as H2SO4.
Markovnikov’s rule applies.
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