Addition means to add
Addition reaction is the characteristic property of
alkenes. Alkenes are unsaturated hydrocarbons or carbon compounds which have
double bonds between two carbon atoms.
These unsaturated hydrocarbons are highly reactive due
to the presence of double bonds.
Addition reaction
When a double bond between two carbon atoms breaks up,
then each carbon atom gets one free electron.
Each electron forms a single covalent bond with other
radicals or groups.
These radicals or groups are added to alkenes to form
saturated hydrocarbon alkanes.
Following are the additional reactions of alkenes
(i) With bromine water
(ii) With hydrogen
(i) With bromine water
All alkenes
undergo an addition reaction. The double bond between carbon atoms broke up and
bromine is added to carbon atoms to form di bromo alkane.
`CH_2=CH_2 + Br_2 →CH_2BR- CH_2Br`
(ii) With hydrogen
When alkenes are heated with hydrogen gas in the
presence of a catalyst like nickel or palladium, they change into alkanes.
This reaction is called hydrogenation.
`CH_2=CH_2 + H_2 →CH_3- CH_3`
Industrial application of hydrogenation
Vegetable oil
like mustard, groundnut, or cottonseed oil has an unsaturated carbon chain.
When hydrogen gas is passed through these oils in the presence of a catalyst like nickel, an
addition reaction takes place, and unsaturated fat changes into saturated fat
which is called vegetable ghee.
`R_2C=CR_2 + H_2 →R_2CH- CHR_2`
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