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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

CombustionAddition reactions :

hydrogenationhalogenationhydrohalogenation 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 is the addition of hydrogen (H2) to a functional group. It requires a catalyst (cat)

HYDROGENATIONHYDROGENATION

+Pd

H2

CH3

HH

CH3

+ H2 CH3CH2CH2CH3

Pt

catalyst = Pt, Pd, Ni

+C C H H C C

H H

catalyst

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.

Bromine adds to the alkene to form colorless dibromo compounds.

Br2

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2. UnSymmetrical addition reactions

HYDROHALOGENATION : The addition of H-Cl, H-Br 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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