Important Reactions of Organic Compounds

8/4/2019 Important Reactions of Organic Compounds

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IMPORTANT REACTIONS

OF CERTAIN ORGANICCOMPOUNDS


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What must you be able to do?

identify the types of reactions that

hydrocarbons undergo.

explain what happens during each type

of reaction.

compare the reactivity of different

hydrocarbons.


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Alkanes undergo:

Combustion (or oxidations) reactions.

Elimination reactions.

Substitution reactions


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COMBUSTION (OXIDATION)

REACTIONS:

Alkanes react with oxygen in the air and

form carbon dioxide and water.

The reaction is exothermic and a great

deal of energy is released.

Methane burns with a blue flame.

CH4 + 2O2 CO2 + H2O + energy


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Propane is the gas used in bunsen burners

in the laboratory. Propane burns as follows:

C3H8 + 5O2 3CO2 + 4H2O + energy

Butane is the fuel in Bic lighters.

2C4H10 + 13O2 8CO2 + 10H2O + energy


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ELIMINATION REACTIONS:

During these reactions an unsaturatedmolecule is formed as well as a second

small molecule (eg. H2 or H2O)

Cracking (heating to a high temperature)produces unsaturated products:

CH3CH3 CH2 = CH2 + H2High temperature


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SUBSTITUTION REACTIONS:

During these reactions a hydrogen atom is

replaced by a halogen atom, forming a halo

-alkane molecule.

Activation energy, in the form of sunlight orheat is needed to start the reaction.

CH4 + Cl2 CH3Cl


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Haloalkanes are important compounds that

are used as anesthetics (trichloromethane),

solvents and dry cleaning agents.

Trichloromethane

(chloroform)

Tetrachloroethane

Tetrachloromethane

(Carbon tetrachloride) Halo-ethane

H


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Alkenes undergo:

Combustion (or oxidations) reactions.

Addition reactions.

Addition polymerisation reactions


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COMBUSTION (OXIDATION)

REACTIONS:

Alkenes react with oxygen in the air and

form carbon dioxide and water.

The reaction is exothermic and a great

deal of energy is released.

Ethene burns with a blue flame.

CH2 = CH2 + 3O2 2CO2 + 2H2O +

energy


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ADDITION REACTIONS

Unsaturated hydrocarbons undergo additionreactions when the double bond opens and

extra atoms add onto the 2 carbon atoms

that were previously joined by a double bond.

Halogen atoms and hydrogen atoms can be

added into the original molecule.


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CH2 = CH2 + HCl Cl CH2 CH3

CH2 = CH2 + Br2 Br CH2 CH2 - Br

The addition of hydrogen to an unsaturated

molecule is known as HYDROGENATION.CH2 = CH2 + H2 CH3 CH3

ethene ethaneThe hydrogenation of unsaturated vegetable

oils hardens the oils and forms margarine.

The oils become more saturated.


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ADDITION POLYMERISATION

During these reactions monomers (smallunsaturated hydrocarbon molecules) add to

themselves to form polymers.

Polypropylene is formed when propylene

molecules join to form long chains of

repeating units:

- CH2CH(CH3) CH2CH(CH3)-CH2CH(CH3)-

CH2CH(CH3)- etc


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Alkynes undergo:

Combustion (or oxidation) reactions.

Addition reactions.


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Ethyne can be prepared by adding water to

calcium carbide:

CaC2 + H2O Ca(OH)2 + C2H2

Ethyne is used, along with oxygen, in an

oxy-acetylene torch, which is used to cutmetals.

The ethyne undergoes combustion,

releasing a great deal of energy.

2C2H2 + 5O2 4CO2 + H2O

H = - 1 310kJ/mol


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ADDITION REACTIONS of alkynes

During addition reactions atoms are added

into the molecule in place of the triple bond. A

double C=C bond remains.


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REACTIONS OF ALCOHOLS

Ethanol can be oxidised to ethanal (analdehyde):

CH3COOH + 8H+ + Cr2O7

2- 3CH3CHO

+ 2Cr3+ + 7H2O

Alcohols react with carboxylic acids to form

an ester.

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Important Reactions of Organic Compounds