CHAPTER 16: Halogen Derivatives
16.1 Introduction to Halogenoalkanes
16.2 Reactions of Halogenoalkanes
16.3 Uses of Halogenoalkanes
Learning outcomes:
(a) recall the chemistry of halogenoalkanes as exemplified by
(i) the following nucleophilic substitution reactions of bromoethane: hydrolysis, formation of
nitriles, formation of primary amines by reaction with ammonia.
(ii) the elimination of hydrogen bromide from 2-bromopropane.
(b) describe the mechanism of nucleophilic substitution (by both SN1 and SN2 mechanisms) in
halogenoalkanes.
(c) interpret the different reactivities of halogenoalkanes(with particular reference to hydrolysis and
to the relative strengths of the C-Hal bonds).
(d) explain the uses of fluoroalkanes and fluorohalogenoalkanes in terms of their relative chemical
inertness.
(e) recognise the concern about the effect of chlorofluoroalkanes on the ozone layer.
, 16.1 Introduction to Halogenoalkaes
What are halogenoalkanes?
1) Halogenoalkanes(or alkyl halides) are compounds in which one or more hydrogen
atoms in an alkane have been replaced by halogen atoms (fluorine, chlorine,
bromine or iodine).
2) Halogenoalkanes can be classified as primary, secondary or tertiary
depending on the number of alkyl groups(R groups) attached to the carbon
atom holding the halogen atom.
3) Some examples of halogenoalkanes:
Chloropropane, 2-bromopropane, 1,2-diiodoethane, ICH₂CH₂I
CH₃CH₂CH₂Cl CH₃CHBrCH₃
Physical properties of halogenoalkanes
1) i. Boiling point of the halogenoalkanes
increases as the molecular size
increases. This is because there are
more electrons in larger molecules
and more temporary dipoles can
be set up, resulting in stronger van der
Waal's forces.
ii. Primary halogenoalkanes have higher boiling point compared to secondary
and tertiary halogenoalkanes of the same molecular weight. This is because
the surface area of primary halogenoalkanes is higher, more
temporary dipoles can be set up, resulting in stronger van der Waal's forces.
16.1 Introduction to Halogenoalkanes
16.2 Reactions of Halogenoalkanes
16.3 Uses of Halogenoalkanes
Learning outcomes:
(a) recall the chemistry of halogenoalkanes as exemplified by
(i) the following nucleophilic substitution reactions of bromoethane: hydrolysis, formation of
nitriles, formation of primary amines by reaction with ammonia.
(ii) the elimination of hydrogen bromide from 2-bromopropane.
(b) describe the mechanism of nucleophilic substitution (by both SN1 and SN2 mechanisms) in
halogenoalkanes.
(c) interpret the different reactivities of halogenoalkanes(with particular reference to hydrolysis and
to the relative strengths of the C-Hal bonds).
(d) explain the uses of fluoroalkanes and fluorohalogenoalkanes in terms of their relative chemical
inertness.
(e) recognise the concern about the effect of chlorofluoroalkanes on the ozone layer.
, 16.1 Introduction to Halogenoalkaes
What are halogenoalkanes?
1) Halogenoalkanes(or alkyl halides) are compounds in which one or more hydrogen
atoms in an alkane have been replaced by halogen atoms (fluorine, chlorine,
bromine or iodine).
2) Halogenoalkanes can be classified as primary, secondary or tertiary
depending on the number of alkyl groups(R groups) attached to the carbon
atom holding the halogen atom.
3) Some examples of halogenoalkanes:
Chloropropane, 2-bromopropane, 1,2-diiodoethane, ICH₂CH₂I
CH₃CH₂CH₂Cl CH₃CHBrCH₃
Physical properties of halogenoalkanes
1) i. Boiling point of the halogenoalkanes
increases as the molecular size
increases. This is because there are
more electrons in larger molecules
and more temporary dipoles can
be set up, resulting in stronger van der
Waal's forces.
ii. Primary halogenoalkanes have higher boiling point compared to secondary
and tertiary halogenoalkanes of the same molecular weight. This is because
the surface area of primary halogenoalkanes is higher, more
temporary dipoles can be set up, resulting in stronger van der Waal's forces.
