Properties of Alkenes and Alkynes

Chemical Properties

Undergo combustion as do alkanes .

Alkenes and Alkenes-reactive at the multiple bond.

Physical Properties

Nonpolar and insoluble in water as are alkanes.

Nonpolar, therefore Boiling points depend on size and shape.

Alkenes may display cis-trans isomerism.

Chemical Reactions of Unsaturated Compounds

Chemical Reactions of Alkenes

Structure of the Double Bond in Alkenes

C C

The two components of the double bond

are pictured the same, but one of the

bonds (the π bond) is actually weaker than

the other.

The characteristic reaction of alkenes is an ADDITION REACTION.

Chemical Reactions of Alkenes

+

“A” and “B” are not necessarily single atoms.

“A” and “B” are added to the structural and

molecular formula.

WHAT ARE “A” AND “B” ? H-H Hydrogenation X-X Halogenation H-X Hydrohalogenation H-OH Hydration

C C C C

A

A"catalyst"

B

B

Chemical Reactions of Alkenes

C C

A B

C C C C

A

A"catalyst"

B

B

C C

A B

C C C CH H

H HNi or Pt catalyst

HC

HC

H

HH C

H

C

H

H

H HH2, Ni or Pt catalyst

H3CC

H3CC

CH3

CH2CH3

H3C C

CH3

C

CH2CH3

CH3

H HH2, Ni or Pt catalyst

Catalytic Hydrogenation

Specific Examples

alkenes alkanes

+

Specific Examples

Catalytic Hydrogenation

C C C CH H

H HNi or Pt catalyst

HC

HC

H

HH C

H

C

H

H

H HH2, Ni or Pt catalyst

H3CC

H3CC

CH3

CH2CH3

H3C C

CH3

C

CH2CH3

CH3

H HH2, Ni or Pt catalyst

ethene ethane

C2H4 C2H6

2,3-dimethyl-2-pentene 2,3-dimethylpentane

C7H14

C7H16

+

Halogenation - Synthesis of Alkyl Halides

C C C CX X

X XDark, no catalyst

HC

HC

H

HH C

H

C

H

H

Cl ClCl2, no catalyst

H3CC

H3CC

H

CH2CH3

H3C C

CH3

C

CH2CH3

H

Cl ClCl2, no catalyst

General Reaction

Specific Examplesalkenes alkylhalides

+

Halogenation - Synthesis of Alkyl Halides

C C C CX X

X XDark, no catalyst

HC

HC

H

HH C

H

C

H

H

Cl ClCl2, no catalyst

H3CC

H3CC

H

CH2CH3

H3C C

CH3

C

CH2CH3

H

Cl ClCl2, no catalyst

General Reaction

Specific Examples

ethene 1,2-dichloroethane

2-methyl-2-pentene 2,3-dichloro-2-methylpentane

C2H4 C2H4Cl2

C6H12

C6H12Cl2

+

Addition of Bromine (Br2)

CH3 CH CH CH2 CH3 CH3 CH CH CH2 CH3

Br BrBr2no catalyst

Br2no catalyst

BrBr

Br2no catalyst No reaction

Chemical Reactions of Alkenes

Addition of Bromine (Br2)

Alkane Alkene Alkane +

Br2

Alkyl Bromide Br2 in

CCl4

Addition of Bromine (Br2)

The result can be quantitated.

Chemical Reactions of Alkenes

The characteristic reaction of alkenes is an ADDITION REACTION.

Chemical Reactions of Alkenes

+

“A” and “B” are not necessarily single atoms.

“A” and “B” are added to the structural and

molecular formula.

WHAT ARE “A” AND “B” ? H-H Hydrogenation X-X Halogenation H-X Hydrohalogenation H-OH Hydration

C C C C

A

A"catalyst"

B

B

Hydrohalogenation-Synthesis of Alkyl halides

C C C CH X

H X

or

C C

X H

+

H3C CH CH CH3H Cl

H3C CH CH CH3

H Cl

H3C CH CH CH3

Cl H

or

Specific Example:

2-chlorobutane

2-chlorobutane

C4H9Cl

C4H8

2-butene

In some cases only one product can be formed.

In some cases two isomeric products are possible:

2-chloropropane

1-chloropropane

propene ?

( )

( )C3H6

C3H7Cl

H3C CH CH2H Cl

H3C CH CH2

H Cl

H3C CH CH2

Cl Hor

H3C CH2 CH2

Cl

H3C CH CH3

Cl

MARKOVINIKOV’S RULE- When adding H-X or H-OH (H2O) to alkenes with different number of groups attached to the double bonds, the “H” portion of the reagent adds to the carbon that has the greater number of hydrogen atoms in the reactant molecule.

H-Cl H-Br H-OH

Major product

1-chloropropane

2-chloropropane

propene

H3C CH CH2H Cl

H3C CH CH2

H Cl

H3C CH CH2

Cl Hor

H3C CH2 CH2

Cl

H3C CH CH3

Cl

What is the result if two isomeric products are possible ??

2-chloropropane

1-chloropropane

propene ?

( )

( )C3H6

C3H7Cl

H3C CH CH2H Cl

H3C CH CH2

H Cl

H3C CH CH2

Cl Hor

H3C CH2 CH2

Cl

H3C CH CH3

Cl

Major product

Hydration of Alkenes-Synthesis of Alcohols

C C C CH OH

H OH

or

C C

HO H

+

H3CC

H3CCCH3

CH3

H3C C

CH3

C

CH3

CH3H OH

H OH

or

H3C C

CH3

C

CH3

CH3

HO H

+

alcoholsalkenes

2,3-dimethyl-2-butene2,3-dimethyl-2-butanol

C6H12

C6H14O

In some cases Markovnikov's rule is not needed.

Hydration of Alkenes

H3CC

H3CCH

CH3

H3C C

CH3

C

CH3

HH OH

H OH

or

H3C C

CH3

C

CH3

H

HO H

+ H3C CH

CH3

CH CH3

OH

H3C C

CH3

CH2 CH3

HO

Major product

2-methyl-2-butene

3-methyl-2-butanol

2-methyl-2-butanol

C5H10

C5H12O

HHO

*

*

AlkynesThe triple bond consists of two π components

and one σ component.

C C

The characteristic reaction is addition to both of the π bonds.

C C C C2 mol of A-B

A

A B

B

Alkynes

Br Br

2 mol Br2no

catalyst

CH3 C C CH3 CH3 C C CH3

Br Br

Cl H

2 mol HClno

catalyst

CH3 C C H CH3 C C H

Cl H

Markovnikov’s rule may or may not apply.

C4H6 C4H6Br4

C3H4 C3H6Cl2

“Addition” Polymers Overall Reaction:

C=CA

B

X

YC=C

A

B

X

YC=C

A

B

X

YC=C

A

B

X

YC=C

A

B

X

Y

C CA

B

X

YC C

A

B

X

YC C

A

B

X

YC C

A

B

X

YC C

A

B

X

Y

Acid or “initiator”

C CA

B

X

Y( ) n n = number of individual units

CH2 CH2

CH2 CH

CH3

CH2 CH

Monomer Polymer Uses

ethylene

(CH2 CH2 )n

polyethylene

(CH2 CH )n

CH3propylene polypropylene

(CH2 CH )n

styrene polystyrene

bottles, toys, housewares, wire cableinsulation, plastic sheeting

outdoor carpeting, food packagingappliance housings

styrofoam containers, food packaginghairbrush handles, toys

“Addition” Polymers

“Addition” Polymers

CH2 CH

Cl

CH2 CH

CN

CF2 CF2

(CH2 CH )n

Cl

vinyl chloride polyvinylchloride (PVC)

(CH2 CH )n

CN

acrylonitrile polyacylonitrile

(CF2 CF2 )n

tetrafluoroethylene polytetrafluoroethylene

home siding, gutters, flooring, garden hose, PVC tubing

acrylic textile fibers

“Teflon”, mechanical parts, cookware, chemical resistant gaskets

Monomer Polymer Uses

polyacrylonitrile

Aromatic Hydrocarbons

Benzene (C6H6) was discovered in 1825, but a partially correct structure was not proposed until 1865 by August Kekule. The structure consisted of six carbons in a ring joined by alternating single and double bonds.

Physical and chemical evidence indicates that benzene behaves as if all the carbon-carbon bonds are identical. Hence, the fol lowing structural representation is sometimes used:

Resonance in Benzene

Delocalized Bonding in Benzene

sigma bondingsystem

sp2 hybridorbitals

remaining p orbitals

delocalized pi bonding

Aromatic Hydrocarbons-Nomenclature1. Identify the benzene ring in a compound and assign the parent name “benzene”

2. Attach names and location of substituents.

3. For two or more substituents, number the benzene ring starting with one of the substituents to give the lowest combination of numbers to the substituents.

4. Some important monosubstituted benzenes have common names:

Toluene Phenol Aniline Benzoic Acid Benzaldehyde

CH3 OH NH2 COHO

CHO

Aromatic Hydrocarbons-Nomenclature

5. The prefixes ortho (o), meta (m), and para (p) are often used to indicate the relative positions of two substituents in 1,2- , 1,3- , and 1,4- placement on a benzene ring.

1,2-dibromobenzene 1-hydroxy-3-nitrobenzene 1-amino-4-chlorobenzene

Br

Br

OH

NO2

NH2

Cl

ortho-dibromobenzene meta-nitrophenol para-chloroaniline

Aromatic Hydrocarbons-Nomenclature

NH2C

H3C

H3C

H

benzene “amino-”“isopropyl-“

1

23

4

4-isopropyl aminobenzene

orpara isopropyl aniline

Aromatic Hydrocarbons-Nomenclature

4. The benzene ring may be named as a subsituent.

4-chloro-2-methyl-6-phenyl-2-heptene

H3C

C

H3C

CH

HC

Cl

CH2 CH

CH3

The Benzene Ring in Drug Molecules

CH3

CH3OH

AspirinIbuprofen

DextromethorphanCinnamedrine

O OH

O

O

CH3OH

O

CH3

CH2CH

CH3

CH3

HO3S—OH

O2N—OH

Cl—Cl

H—OH

H—OH

H—Cl

Aromatic Hydrocarbons Substitution Reactions

?

H H

H

HH

H Y X +

H H

Y

HH

H+ H X

Y is substituted for H

Aromatic Hydrocarbons Substitution Reactions

H

H

H

H

H

HCl2Fe

H

Cl

H

H

H

H

C6H6 C6H5Cl

H

H

H

H

H

HH2SO4heat

HSO3H

H

H

H

H

C6H6 C6H5SO3H

Aromatic Hydrocarbons Substitution Reactions

H

H

H

H

H

HHNO3heat

HNO2

H

H

H

H

C6H6 C6H5NO2

CH3

H

H

H

H

HHNO3heat

HNO3heat

HNO3heat

CH3

NO2

H

NO2

H

O2N

Tri Nitro Toluene