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OCR A Level Chemistry A – Module 4 Core Organic Chemistry

4.2.2
Haloalkanes

Section 4.2.2 covers hydrolysis of haloalkanes by aqueous alkali and by water with silver nitrate in ethanol, the definition of a nucleophile, the mechanism of nucleophilic substitution for primary haloalkanes, the trend in rates of hydrolysis explained by carbon–halogen bond enthalpies, and the production of halogen radicals from CFCs and the catalysed breakdown of ozone by Cl• and •NO.

Exam Paper
Paper 2 & 3
H432/02 and H432/03
Specification Points
4.2.2 (a) – (e)
5 learning outcomes
Topic Parts
5 pages
Revision notes available
Exam Board
OCR A
H432 (2015 onwards)

Revision Notes

Work through 4.2.2 Haloalkanes in a structured sequence.

Seven types
Reaction Types
and Mechanisms
1
Available

Reaction Types, Mechanisms and Nucleophiles

Organic reaction types and mechanisms: addition, elimination, substitution, oxidation, reduction, hydrolysis, polymerisation, curly arrows, heterolytic fission, electrophiles, nucleophiles and bond polarity.

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C–X bond
Haloalkanes
and Bonding
2
Available

Haloalkanes: Naming, Classification and the C–X Bond

Haloalkanes: nomenclature and formulae, primary, secondary and tertiary, the polar carbon–halogen bond, bond enthalpies and uses.

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Lone pair attacks δ+
Nucleophilic
Substitution
3
Available

Nucleophilic Substitution Reactions

Nucleophilic substitution of haloalkanes: hydroxide, water, ammonia and cyanide as nucleophiles, conditions, products and the curly-arrow mechanism.

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AgNO₃ in ethanol
Rates of
Hydrolysis
4
Available

Rates of Hydrolysis and Bond Enthalpy

Rates of hydrolysis of haloalkanes: the silver nitrate experiment, precipitate colours, bond enthalpy trend for C–Cl, C–Br and C–I, and primary, secondary and tertiary comparison.

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Cl• catalyst
CFCs and
Ozone
5
Available

CFCs and the Ozone Layer

CFCs and the ozone layer: chlorine radicals, the equations for ozone decomposition, the catalytic cycle, legislation and HFC alternatives.

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Specification Coverage

4.2.2 Haloalkanes – OCR A Level Chemistry A

The following OCR A learning outcomes state what candidates should be able to do. Wording is taken from the OCR A Level Chemistry A (H432) specification.

4.2.2 Haloalkanes

4.2.2(a)(i)
hydrolysis of haloalkanes in a substitution reaction by aqueous alkali
4.2.2(a)(ii)-a
hydrolysis of haloalkanes in a substitution reaction by water in the presence of AgNO₃ and ethanol
4.2.2(a)(ii)-b
use of hydrolysis by water in the presence of AgNO₃ and ethanol to compare experimentally the rates of hydrolysis of different carbon–halogen bonds
4.2.2(b)
definition and use of the term nucleophile (an electron pair donor)
4.2.2(c)
the mechanism of nucleophilic substitution in the hydrolysis of primary haloalkanes with aqueous alkali (see also 4.1.1 h–i)
4.2.2(d)
explanation of the trend in the rates of hydrolysis of primary haloalkanes in terms of the bond enthalpies of carbon–halogen bonds (C–F, C–Cl, C–Br and C–I)
4.2.2(e)-i
production of halogen radicals by the action of ultraviolet (UV) radiation on CFCs in the upper atmosphere
4.2.2(e)-ii
the catalysed breakdown of the Earth’s protective ozone layer resulting from halogen radicals
4.2.2(e)(i)
equations to represent the production of halogen radicals
4.2.2(e)(ii)
equations to represent the catalysed breakdown of ozone by Cl· and other radicals e.g. ·NO