Chapter 3.1-ALKENE (1).pdf

CHAPTER 3: UNSATURATED HYDROCARBON ALKENES

Unsaturated Hydrocarbon

Hydrocarbons that do not contain the maximum amount of hydrogen

NOT all carbon atoms have four single covalent bonds

One or more double bonds or triple bonds between carbon atoms

Alkenes

hydrocarbons that contain double covalent bonds

General formula for alkenes with one double bond is CnH2n

Alkenes are nonpolar

show trends in properties similar to those of alkanes in boiling points and physical states.

EX:

-farnesene, a solid at room temperature, is found in the natural wax covering of apples

Properties of Alkenes

H3C

C

HC

CH2

H2C

C

HC

CH2

HC

C

HC

CH2

CH3 CH3 CH3

Rules similar to naming alkanes

parent hydrocarbon

longest continuous chain of carbon atoms that contains the double bond

Number so the double bond has the lowest number

Systematic Names of Alkenes

pentene

H2C CH2C

H2C CH3

H2C CH3

hexane

H2C CH2C

H2C CH3

H2C CH3

not:

1-pentene

H2C CH2C

H2C CH3

H2C CH3

1 2 3 4 5

IUPAC RULES

RULE 1. Select the longest continuous carbon chain that contains a double bond.

This chain

contains 6

carbon atoms

RULE 2. Name this compound as you would an alkane, but change ane to ene for an alkene.

This chain

contains 8

carbon atoms

This is the longest

continuous chain.

Select it as the parent

compound.

Name the parent

compound octene.

RULE 3. Number the carbon chain of the parent compound starting with the end nearer to the double bond. Use the smaller of the two numbers on the double-bonded carbon to indicate the position of the double bond. Place this number in front of the alkene name.

IUPAC RULES

This end of the chain is closest to the double bond. Begin numbering here.

The name of the parent compound is 1-octene.

IUPAC RULES

8

7

4 3 2 1

6

5

RULE 4. Branched chains and other groups are treated as in naming alkanes. Name the substituent group, and designate its position on the parent chain with a number.

IUPAC RULES

This is an ethyl group.

8

7

4 3 2 1

6

5

The ethyl group is attached to carbon 4.

4

4-ethyl-1-octene

A compound with more than one double bond.

- Two double bond: diene

- Three double bond: triene

- Four double bond: tetraene

* Numbers are used to specify the locations of the double bonds.

CH2 C C CH2H H

IUPAC names: 1,3-butadiene 1,3,5-heptatriene

new IUPAC names: buta-1,3-diene hepta-1,3,5-triene

1 2 3 4

CH3 C C C C C CH2

12347 6 5

H H H H H

1 2

3

47

6 5

8

IUPAC names: 1,3, 5, 7-cyclooctatetraene

new IUPAC names: cycloocta-1,3,5,7-tetraene

CYCLOALKENES

Contains C=C in the ring

cyclopropene cyclobutene cyclohexenecyclopentene

Nomenclature of cycloalkenes:

- Similar to that alkenes

General formula CnH2n-2 where n =3,4,5..

CH31

2

34

5

6

1

23

4

5

1-methylcyclohexene 1,5-dimethylcyclopentene

1) Replace the -ane ending of the cycloalkane having the same number of carbons by -ene.

2) Number through the double bond in the direction that gives the lower number to the first-appearing substituent.

6-Ethyl-1-methylcyclohexene CH3

CH2CH3

1

2 3

4

5 6

NAMING CYCLOALKENES

Number substituted cycloalkenes in the way that gives the carbon atoms of the double bond the 1 and 2 positions. That also gives the substituent groups the lower numbers at the first point of difference.

5

1

4

2

3

CH3 2

3

1

4

6

5

CH3CH3

1-methylcyclopentene 3,5-dimethylcyclohexene

NOMENCLATURE OF cis-trans

ISOMERS

cis two particular atoms (or groups of atoms) are adjacent to each other

trans the two atoms (or groups of atoms) are across from each other

C CH3C

H

CH2CH3

H

C CH3C

H

H

CH2CH3

cis-2-pentene trans-2-pentene

geometric isomers (diastereomers)

C=C are called vinyl carbons

If either vinyl carbon is bonded to two equivalent groups, then no geometric isomerism exists.

CH3CH=CHCH3 CH3CH2CH=CH2

YES NO

CH3 (CH3)2C=CHCH3 CH3CH=CCH2CH3 NO YES

Confusion about the use of cis- and trans-. According to IUPAC rules it refers to the parent chain.

cis-

????????

C C

H

H3C CH2CH3

CH3

C C

H3C

H Br

Cl

E/Z system is now recommended by IUPAC for the designation of geometric isomerism.

1. Use the sequence rules to assign the higher priority * to the two groups attached to each vinyl carbon.

2. * * *

*

(Z)- zusammen (E)- entgegen

together opposite

C C

H

H3C CH2CH3

CH3

C C

H3C

H Br

Cl

*

* *

*

(Z)-

(E)-

C C

H

H3C CH2CH3

CH3

C C

H3C

H Br

Cl

*

* *

*

(Z)-3-methyl-2-pentene

(3-methyl-cis-2-pentene)

(E)-1-bromo-1-chloropropene

CH3

CH3CH2 CHCH2CH3

/

C = C 3-ethyl-5-methyl-3-heptene

/

CH3CH2 H (NOT a geometric isomer)

SYNTHESIS OF ALKENES


DeHydration

Removal of Water

DeHydrohalogenation

Removal of Hydrogen Halides


Alkenes can be prepared in the following ways:

i) Dehydration of alcohols

conc. H2SO4

R-CH2-CH2-OH R-CH=CH2 + H2O

Loss of H and OH from adjacent carbons. Acid catalyst is necessary. (H2SO4 / H3PO4) The reactions are carried out at high temperature; depending on type of alcohols used.


Alkenes can be prepared in the following ways:

ii) Dehydrohalogenation of haloalkanes

*CH3CH2O-Na+ in

ethanol

R-CH2-CH2-X

(reflux)

R-CH=CH2 + HX

*Potassium ethoxide

Loss of H and halogen (X) from an alkyl halide

In the presence of strong base in solvent

Saytzeff rule:

- A reaction that produces an alkene would favour the formation of an alkene that has the greatest number of substituents attached to the C=C group.

CH3CH2-CH-CH3OH

H+

H+

CH3CH=CH-CH3 + H2O

CH3CH2-CH=CH2 + H2O

2-butanol2-butenemajor product

1-butene

CH3CH-CH-CH2

BrH H

KOH CH3CH=CH-CH3 CH3CH2CH=CH2alcohol

reflux

2-bromobutane2-butene

(major product)1-butene

Dehydration of alcohols

Dehydrohalogenation of haloalkanes

REACTION OF ALKENES

REACTION OF ALKENES

Hydrogenations Addition of Hydrogen

Halogenation

Addition of Halogen

Hydrohalogenation

Addition of Hydrogen Halides

Hydration

Addition of Water

Ozonolysis

Reaction of Alkenes

Primarily reactions involve the double bond

The key reaction of double bond is addition reaction (Breaking the bond and adding something to each carbon)

+ A - B

A B

The major alkene reactions include additions of hydrogen (H2),halogen ( CI2 or Br2), water (HOH) or hydrogen halides (HBr or HCI)

Why do alkenes undergo addition reactions?

Addition Reactions

Carbon-carbon double bonds in alkenes are reactive.

readily undergoes addition reactions

In an addition reaction, carbon-carbon double bonds become single bonds. This means that an unsaturated hydrocarbon becomes a saturated organic compound.

+

Unsaturated

hydrocarbon

Saturated organic

compound

(1) Catalytic hydrogenation:

- hydrogenation: addition of hydrogen to a double bond and triple bond to yield saturated product.

- alkenes will combine with hydrogen in the present to catalyst to form alkanes.

C C H H C C

H H

Pt or Pd

25-90oC

- Plantinum (Pt) and palladium (Pd) Catalysts

- Pt and Pd: temperature 25-90oC

- Nickel can also used as a catalyst, but a higher temperature of 140oC 200oC is needed.

Reaction of Alkenes

H2C CH2 H2Pt

CH3CH2CH2CH2CH CH2 H2Pt

H3C CH3

CH3CH2CH2CH2CH2CH3

EXAMPLES:

ethylene ethanelow pressure

low pressurehexene hexane

(2) Addition of halogens:

i) In inert solvent:

- alkenes react with halogens at room temperature and in dark.

- the halogens is usually dissolved in an inert solvent such as dichloromethane (CH2Cl2) and tetrachloromethane (CCl4).

- Iodine will not react with alkenes because it is less reactive than chlorine and bromine.

- Fluorine is very reactive. The reaction will produced explosion.

C C X X C C

X X

inert solvent

X X = halogen such as Br2 or Cl2Inert solvent = CCl4 or CH2Cl2

Reaction of Alkenes

EXAMPLES:

C C

HH

H H Br Br

Br2

Br

Br

CCl4

CH3CH=CH2 Cl2CCl4

CH3CH

Cl

CH2

Cl

C C

Br

H H

Br

H H

inert solvent (CCl4)

ethene1,2-dibromoethane

* the red-brown colour of the bromine solution will fade and the

solution becomes colourless.

cyclohexene1,2-dibromocyclohexane

propene 1,2-dichloropropane

(3) Addition of hydrogen halides:

- Addition reaction with electrophilic reagents.

- Alkenes react with hydrogen halides (in gaseous state or in aqueous solution) to form addition products.

- The hydrogen and halogen atoms add across the double bond to form haloalkanes (alkyl halides).

- General equation:

C C C C

H X

HX

alkene haloalkane

- Reactivity of hydrogen halides : HF < HCl < HBr < HI

Reaction of Alkenes

* Reaction with HCl needs a catalyst such as AlCl3

H2C CH2 HClAlCl3

CH3CH2Cl

H-I

CH3CH=CHCH3 + H-Br

I

CH3CH2CHCH3

Br

EXAMPLES:

cyclopentene iodocyclopentane

2-butene 2-bromobutane

MARKOVNIKOVS RULE

There are 2 possible products when hydrogen halides react with an unsymmetrical alkene.

It is because hydrogen halide molecule can add to the C=C bond in two different ways.

C C

H

HCH3

H

H-I

C C

H

HCH3

H

H-I

C C

H

HCH3

H

H I

C C

H

HCH3

H

I H

1-iodopropane

2-iodopropane

(major product)

Markovnikovs rules:

- the addition of HX to an unsymmetrical alkene, the hydrogen atom attaches itself to the carbon atom (of the double bond) with the larger number of hydrogen atoms.

(5) Addition reaction with acidified water (H3O+): hydration of

alkenes

Hydration: The addition of H atoms and OH groups from water molecules to a multiple bond.

Reverse of the dehydration reaction.

Direct hydration of ethene:

- passing a mixture of ethene and steam over phosphoric (v) acid (H3PO4) absorbed on silica pellets at 300

oC and a pressure of 60 atmospheres.

- H3PO4 is a catalyst.

CH2=CH2 H2OH3PO4

CH3CH2OH(g) (g)300

oC, 60 atm

(g)

ethene ethanol

C C H2O C C

H OH

alkene alcohol

H+

Markovnikovs rule is apply to the addition of a water molecule across the double bond of an unsymmetrical

alkene.

For examples:

CH3 C CH2

CH3

H OH H+

CH3CH=CH2 + H2O CH3CHCH3

OH

CH3 C CH2

CH3

OH H

25oC

2-methylpropene

tert-butyl alcohol

propene

2-propanol

H+

H+ = catalyst

(5) Ozonolysis:

- The reaction of alkenes with ozone (O3) to form an ozonide, followed by hydrolysis of the ozonide to produce aldehydes and /or ketone.

- Widely used to determine the position of the carbon-carbon double bond.

- Ozonolysis is milder and both ketone and aldehydes can be recovered without further oxidation.

OZONOLYSIS OF ALKENES

C C

R

R

R'

H

O3 C

O O

CO R'

H

R

R

(CH3)2S

C O

R

RCO

R'

Hozonide ketone aldehyde

or H2O, Zn/H+

EXAMPLES:

H

OCH3CH3O

H

H

O

O

OCH3

H

O

CH3O

O

H

O

H

Oi) O3

ii) (CH3)2S3-nonene

i) O3

ii) (CH3)2S

Ethylene and propylene are the largest-volume industrial organic chemicals.

Used to synthesis a wide variety of useful compounds.

USES OF ALKENES

CH3 C

O

OH

CH2 CH2

CI CI

Cl2C C

H

H

H

H

CH3 C

O

H

O2

C C

CIH

H H

CH3 CH2

OH

NaOH

C C

H H

HH

H+

H2O

CH2 CH2

OHOH

O

H2C CH2

n

polyethylene

polymerize

acetaldehyde

oxidize

oxidize

acetic acid

ethylene ethylene dichloride

vinyl chloride

H2O

catalyst

Ag catalystethylene oxide

ethylene glycol ethanol

The most popular plastic.

Uses:

i) Grocery bags

ii)Shampoo bottles

iii)Children's toy

iv)Bullet proof vests

v)Film wrapping

vi)Kitchenware

POLYETHENE (PE)

POLYVINYL CHLORIDE (PVC)

C C

H H

CIH C C

H

H

CI

H

C

H

H

C

CI

H

C

H

H

C

CI

Hnvinyl chloride

polymerize

poly(vinyl chloride)PVC, "vinyl"

USES OF PVC: Clothing - PVC fabric has a sheen to it and is waterproof. - coats, shoes, jackets, aprons and bags. As the insulation on electric wires. Producing pipes for various municipal and industrial

applications. For examples, for drinking water distribution and wastewater mains.

As a composite for the production of accessories or housings for portable electronics.

uPVC or Rigid PVC is used in the building industry as a low-maintenance material.

Ceiling tiles.

USES OF ETHANOL

Motor fuel and fuel additive. As a fuel to power Direct-ethanol fuel cells (DEFC) in order to

produce electricity. As fuel in bipropellant rocket vehicles. In alcoholic beverages. An important industrial ingredient and use as a base chemical

for other organic compounds include ethyl halides, ethyl esters, diethyl ether, acetic acid, ethyl amines and to a lesser extent butadiene.

Antiseptic use. An antidote. Ethanol is easily miscible in water and is a good solvent.

Ethanol is less polar than water and is used in perfumes, paints and tinctures.

Ethanol is also used in design and sketch art markers. Ethanol is also found in certain kinds of deodorants.

In short, cracking is used to produce:

Petrol (fuel) Short-chain alkenes

(starting materials for

making ethanol and

plastics)

Hydrogen (fuel and raw material

for Haber process)

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Chapter 3.1-ALKENE (1).pdf