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OCR A Level Chemistry A

4.1.3
Alkenes

OCR 4.1.3 covers the bonding in alkenes, E/Z and cis–trans stereoisomerism with the Cahn–Ingold–Prelog priority rules, electrophilic addition and Markownikoff’s rule, the addition reactions of alkenes with hydrogen, halogens, hydrogen halides and steam, addition polymerisation, and the processing of waste polymers.

Exam Paper
Paper 2
H432/02, also Paper 3
Specification Points
4.1.3(a) – 4.1.3(l)
12 learning outcomes
Topic Parts
7 parts
Revision notes available
Exam Board
OCR A
OCR H432

Revision Notes

Work through each part of OCR 4.1.3 in a structured sequence.

C=C bond
Alkene
Bonding
1

Alkene Bonding

The carbon-carbon double bond as a σ bond and a π bond, the trigonal planar shape and why the π bond makes alkenes reactive.

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Stereoisomers
Geometric
Isomerism
2

Geometric Isomerism

Restricted rotation, E/Z and cis–trans stereoisomerism, and the Cahn–Ingold–Prelog priority rules.

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Curly arrows
Electrophilic
Addition
3

Electrophilic Addition Mechanism

Electrophiles, heterolytic fission, carbocation intermediates and how to draw the mechanism.

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Addition reactions
Reactions of
Alkenes
4

Reactions of Alkenes

Addition of hydrogen, halogens, hydrogen halides and steam, the bromine test and Markownikoff’s rule.

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Addition polymers
Polymerisation
Reactions
5

Polymerisation Reactions

Addition polymerisation of alkenes and substituted alkenes, repeat units and monomers.

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Sustainability
Polymer
Waste
6

Polymer Waste

Combustion for energy, use as a feedstock, removal of toxic waste products, and biodegradable and photodegradable polymers.

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Sustainability
Waste
Polymers
7

Processing Waste Polymers

Combustion for energy production and use as an organic feedstock: the sustainability benefits of processing waste polymers.

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Specification Coverage

4.1.3 Alkenes – OCR A Level Chemistry A

The following OCR learning outcomes state what learners should be able to demonstrate and apply their knowledge and understanding of for 4.1.3 Alkenes. Wording is taken from the OCR A Level Chemistry A (H432) specification, version 2.8.

4.1.3 Alkenes

4.1.3(a)
alkenes as unsaturated hydrocarbons containing a C=C bond comprising a π-bond (sideways overlap of adjacent p-orbitals above and below the bonding C atoms) and a σ-bond (overlap of orbitals directly between the bonding atoms) (see also 4.1.2 a); restricted rotation of the π-bond
4.1.3(b)
explanation of the trigonal planar shape and bond angle around each carbon in the C=C of alkenes in terms of electron pair repulsion (see also 2.2.2 g–h, 4.1.2 b)
4.1.3(c)
(i) and (ii) below:
(i)
explanation of the terms: stereoisomers (compounds with the same structural formula but with a different arrangement in space); E/Z isomerism (an example of stereoisomerism, in terms of restricted rotation about a double bond and the requirement for two different groups to be attached to each carbon atom of the C=C group); cis–trans isomerism (a special case of E/Z isomerism in which two of the substituent groups attached to each carbon atom of the C=C group are the same)
(ii)
use of Cahn–Ingold–Prelog (CIP) priority rules to identify the E and Z stereoisomers
4.1.3(d)
determination of possible E/Z or cis–trans stereoisomers of an organic molecule, given its structural formula
4.1.3(e)
the reactivity of alkenes in terms of the relatively low bond enthalpy of the π-bond
4.1.3(f)
addition reactions of alkenes with:
(i)
hydrogen in the presence of a suitable catalyst, e.g. Ni, to form alkanes
(ii)
halogens to form dihaloalkanes, including the use of bromine to detect the presence of a double C=C bond as a test for unsaturation in a carbon chain
(iii)
hydrogen halides to form haloalkanes
(iv)
steam in the presence of an acid catalyst, e.g. H3PO4, to form alcohols
4.1.3(g)
definition and use of the term electrophile (an electron pair acceptor)
4.1.3(h)
the mechanism of electrophilic addition in alkenes by heterolytic fission (see also 4.1.1 h–i)
4.1.3(i)
use of Markownikoff’s rule to predict formation of a major organic product in addition reactions of H–X to unsymmetrical alkenes, e.g. H–Br to propene, in terms of the relative stabilities of carbocation intermediates in the mechanism
4.1.3(j)
addition polymerisation of alkenes and substituted alkenes, including:
(i)
the repeat unit of an addition polymer deduced from a given monomer
(ii)
identification of the monomer that would produce a given section of an addition polymer
4.1.3(k)
the benefits for sustainability of processing waste polymers by:
(i)
combustion for energy production
(ii)
use as an organic feedstock for the production of plastics and other organic chemicals
(iii)
removal of toxic waste products, e.g. removal of HCl formed during disposal by combustion of halogenated plastics (e.g. PVC)
4.1.3(l)
the benefits to the environment of development of biodegradable and photodegradable polymers