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Chemical Reactions of Halogenoalkanes
Reactions of halogenoalkanes involve breaking the carbon-halogen bond.

The bond can break homolytically or heterolytically.

Homolytic Fission
Homolytic fission forms radicals.

One way this can occur is when radiation of the right frequency (visible or ultraviolet) is
absorbed by the halogenoalkanes.

For example, with chloromethane:




We…

Page 2

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The Carbon-Halogen Bond
Halogens are much more electronegative than carbon.

So, the carbon-halogen bond is polar.

The + carbon doesn't have enough electrons. This means it can be attacked by a
nucleophile.

A nucleophile is an electron-pair donor.

It donates an electron pair to somewhere without enough electrons.

OH-, NH3…

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Water as a Nucleophile
The water molecule has a lone pair of electrons on the oxygen atom, so water can act as a
nucleophile and attack a halogenoalkanes molecule such as 1-bromobutane ­ though this
reaction is slow than the reaction with OH- ions.

The substitution reaction goes in two…

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Using Nucleophilic Substitution to make Halogenoalkanes
When a halogenoalkane reacts with OH- ions, a nucleophilic reaction occurs and an alcohol
is formed.

You can use the reverse of this reaction to produce a halogenoalkane from an alcohol if you
chose the reaction conditions carefully.

It is another nucleophilic substitution reaction,…

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