s
er
ap
eP
m
e
tr
.X
w
w
w
om
.c
Scheme of work – Cambridge International AS Level Physical Science (8780)
CHEMISTRY – SECTION IV
Unit 5: Organic Chemistry
Recommended prior knowledge
Unit 1 (Theoretical Chemistry) should have been studied before this unit. Although most of Unit 2 is not immediately relevant to this unit, some prior discussion of
bond energies, acids and bases, and kinetics of reactions, would be beneficial.
Context
This unit can either precede or follow Units 2, 3 and 4 (see comment above).
Outline
The unit covers the formulae, names and shapes of organic compounds; isomerism; alkanes; alkenes; halogenoalkanes
(with a mention of primary amines); alcohols; aldehydes; ketones, carboxylic acids and addition polymerisation.
Syllabus ref
Learning objectives
Suggested teaching activities
Learning resources
General rules of nomenclature could be given at the start, i.e.
finding the longest chain; numbering of substituents from the
end that gives the lowest numbers; the general shape of a
name: prefix-stem-suffix. More specific examples could be
covered when functional groups are dealt with in detail.
Practise translating name into structural formula and vice
versa.
Chemistry for Advanced Level 22.4-22.5
Advanced Chemistry 109
AS Level and A Level Chemistry 15.1
Candidates should be able to:
C12(a)
interpret, and use the nomenclature,
general formulae, structural formulae and
displayed formulae of the following classes
of compound:
(i) alkanes and alkenes
(ii) halogenoalkanes
(iii) alcohols (including primary, secondary
and tertiary)
(iv) aldehydes and ketones
(v) carboxylic acids and esters
(vi) amines (primary only) and nitriles
Candidates will be expected to recognise
the shape of the cyclohexane ring.
v2 2Y07
site 8 (organic general principles)
Distinguish between the general/molecular formula (e.g.
C3H7Cl), the structural formula (e.g. (CH3)2CHCl or
CH3CH2CH2Cl) and the displayed formula, which shows all
bonds as lines (but also includes all atoms, incl. H atoms.
Except for ring compounds such as cyclohexane the “skeletal”
Cambridge International AS Level Physical Science (8780)
1
Syllabus ref
Learning objectives
Suggested teaching activities
[Knowledge of benzene or its compounds
is not required.]
formulae, showing bonds but not C or H atoms, will not be
required in structural or displayed formulae.
interpret, and use the following terminology
associated with organic reactions:
(i) functional group
(ii) homolytic and heterolytic fission
(iii) free radical, initiation, propagation,
termination
(iv) nucleophile, electrophile
(v) addition, substitution, elimination,
hydrolysis
(vi) oxidation and reduction.
These terms should be introduced when the reactions of the
relevant functional group are being studied.
C12(c)
describe the shapes of the ethane and
ethene molecules
C12(d)
predict the shapes of other related
molecules
ethane: tetrahedral and 3-dimensional
ethene: trigonal planar and 2-dimensional
The tetrahedral arrangement of bonds around a 4-coordinated
(sp3) carbon atom, and the trigonal arrangement of bonds
around a 3-coordinated (sp2) carbon atom. The use of
molecular models would help greatly here. No understanding
of hybridisation is required. The shapes should be explained in
terms of equal/almost equal repulsion between four or three
bonding electron pairs.
C12(e)
explain the shapes of the ethane and
ethene molecules in terms of σ and π
carbon-carbon bonds
The π bond being due to the sideways overlap of two 2p
orbitals, creating electron density above and below the plane
of the molecule, and restricting rotation about the bond (see
also Section C3)
C12(f)
describe structural isomerism
C12(g)
describe cis-trans isomerism in alkenes,
and explain its origin in terms of restricted
rotation due to the presence of π bonds
Relate to nomenclature. Include chain isomerism (butane, 2methylpropane), positional isomerism (propan-2-ol and
propan-1-ol) and functional group isomerism (propanal and
propanone).
C12(b)
Learning resources
Chemistry for Advanced Level 22.7-22.8
Advanced Chemistry 109
[in equations for organic redox reactions, the symbols [O] and
[H] are acceptable]
Chemistry for Advanced Level 22.6, 23.2
Advanced Chemistry 109, M110
AS Level and A Level Chemistry 15.4
c
a
C
b
Chemistry for Advanced Level 22.3
Advanced Chemistry 109
AS Level and A Level Chemistry 16b.7
C
d
Students sometimes find this concept difficult to understand
v2 2Y07
Cambridge AS Level Physical Science (8780)
2
Syllabus ref
Learning objectives
Suggested teaching activities
Learning resources
and even more difficult to explain.
If the diagram represents a molecule which exhibits cis-trans
isomerism, then a ≠ b and c ≠ d (it doesn’t matter if a is the
same as c or d etc.)
Emphasise that the groups at the first end of the double bond a
and b, must be different from each other and the groups at the
other end of the double bond, c and d must be different from
each other.
C12(h)
deduce the possible isomers for an organic
molecule of known molecular formula
Suitable examples are C5H12, C5H10 (incl. rings), C4H10O
(mention ethers in passing), C4H8O2 (acids and esters). Give
practice in reading the various ways that formula can be
written, including structural and displayed formulae.
C12(i)
identify cis-trans isomerism in a molecule of
given structural formula
Give practice with various structures (e.g. the three
dichloroethenes; alkenes up to C6).
C13(a)
explain the use of crude oil as a source
hydrocarbons
Brief outline of fractional distillation - separation according to
boiling point. [This can be demonstrated with a synthetic
mixture of 40-60 petroleum ether; methylbenzene and paraffin
(kerosene)]. Fractions are mixtures; not all molecules have the
same chain length or number of C atoms due to branched
chains having lower b.pts. than straight chains.
Chemistry for Advanced Level 23.3
Advanced Chemistry 111
AS Level and A Level Chemistry 16c.21
Teaching AS Practical Skills 25
C13(b)
be aware of the general unreactivity of
alkanes, including towards polar reagents
Due to lack of polarity in, and strength of, the C-H and C-C
bonds. High activation energy.
Chemistry for Advanced Level 23.5
Advanced Chemistry 111
AS Level and A Level Chemistry 16a.3
C13(c)
describe the chemistry of alkanes involved
in:
(i) combustion.
Students should generate balanced equations for the complete
combustion of CH4, C2H6, C8H18. Practical work could include
an estimate of the ∆Hoc of various alkanes by burning known
masses underneath a copper calorimeter or similar.
Chemistry for Advanced Level 23.5
Advanced Chemistry 111
AS Level and A Level Chemistry 16a.4
Teaching AS Practical Skills 24
(ii) substitution by chlorine and by bromine
In the presence of UV light, giving poly- as well as monosubstituted halogenoalkanes. Give the balanced equations.
Best demonstrated with C6H14 + Br2.
site 4 (alkanes)
site 7 (N-ch3-04,06)
Describe the mechanism of free-radical
There is only one initiation reaction. Emphasise the multiplicity
C13(d)
v2 2Y07
Cambridge AS Level Physical Science (8780)
Chemistry for Advanced Level 23.4
AS Level and A Level Chemistry 16a.5,
3
Syllabus ref
C13(e)
Learning objectives
Suggested teaching activities
Learning resources
substitution with particular reference to the
initiation, propagation and termination
reactions
of possible halogenated products; i.e. the halogenoalkane
product of one reaction cycle can undergo subsequent
substitution reaction. The sum of the two propagation
equations equals the overall stoichiometric equation. The
termination stage comprising of the combining together of any
two of the free radial species present/formed in the reaction
mixture. Mention that alky free radicals can, join together in a
termination stage; e.g. the 4-carbon by-products obtained
from ethane.
16c.
describe the chemistry of alkenes as
exemplified, where relevant, by the
following reactions:
(i) addition of hydrogen, steam, hydrogen
halides and halogens
The addition of hydrogen to ethene (Ni catalyst) is never
carried out commercially, but mention unsaturated oils →
margarine. The other three reagents undergo electrophilic
addition. Steam (with H3PO4 catalyst) is a useful manufacture
of ethanol. Hydrogen halides give a monohalogenoalkane. Br2
+ alkenes (emphasise that light is not needed) is a good test
for a C=C bond.
Discussed in Section C16.
Chemistry for Advanced Level 24.3
Advanced Chemistry 112
AS Level and A Level Chemistry 16b.9-13
Teaching AS Practical Skills 26
(ii) addition polymerisation (see Section
C16)
C13(f)
CH3CH
CHCH3
Br
Br
C13 (g)
v2 2Y07
Polarisation of Br2 into Brδ+Brδ– by the C=C double bond,
followed by electrophilic addition giving a carbocation + Br–,
which then react together. Mention of the cyclic bromonium ion
is not essential, and may confuse students.
describe the mechanism of electrophilic
addition in symmetrical alkenes, using
bromine/ethene as an example
→ CH3CH
Br
site 4 (alkenes)
site 16 (org chem.)
site 21a
Chemistry for Advanced Level 24.3
Advanced Chemistry 112
+
CHCH3 In the mechanism ‘curly arrows’ should be drawn to show the
movement of electron pairs. One arrow should be from the
C=C bond to the top of the Br–Br molecule; another from the
:Br−
centre of the Br–Br bond to the lower Br atom. An intermediate
bromocarbocation should be drawn. The final curly arrow
should be drawn from the lone pair on the Br– ion towards the
+ve carbon.
suggest how 'cracking' can be used to
obtain more useful alkanes and alkenes of
lower Mr from larger hydrocarbon
molecules
This makes more use of those hydrocarbons that are
commonest in crude oil, but are not particularly useful in
themselves, by breaking up longer chain alkanes into shorter
ones, plus alkenes or hydrogen, using zeolites (catalytic
cracking) or heat (thermal cracking). Student practical on
Cambridge AS Level Physical Science (8780)
Chemistry for Advanced Level 23.3/4/5
Advanced Chemistry 111
AS Level and A Level Chemistry
16a.4,16c.21
Teaching AS Practical Skills 24, 25
4
Syllabus ref
Learning objectives
Suggested teaching activities
Learning resources
cracking.
AS Level and A Level Chemistry 16c.23-27
site 4 (alkanes)
site 7 (N-ch3-04,06)
C13(h)
describe and explain how the combustion
reactions of alkanes lead to their use as
fuels in industry, in the home and in
transport
A survey of the various energy sources (oil, gas, coal) used in
local homes, colleges, offices and factories, and where the fuel
comes from.
C13(i)
recognise the environmental consequences
of carbon monoxide, oxides of nitrogen and
unburnt hydrocarbons arising from the
internal combustion engine and of their
catalytic removal (see Section C10)
The poisonous nature of CO (→ carboxyhaemoglobin); NOx
causing smog, acid rain (on their own, and as a catalyst for
H2SO4 production from SO2); unburnt h/c → smog. Use of PtRh catalyst in car exhaust systems. Main reactions are CO +
NO; CO + O2; CnHm + O2.
C14(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
describe the SN2 mechanism of
nucleophilic substitution in
halogenoalkanes.
C14(b)
H
CH3
C
.. H
OH−
C15(a)
v2 2Y07
H
Br
CH3
C
.. H
NH3
N
+
site 4 (haloalkanes)
site 7 (N-ch3-08)
Note especially the change of solvent for NaOH from water to
ethanol.
The essential features are the curly arrows showing the
formation of the bond to carbon from the lone pair on the
nucleophile, and the C–Br bond breaking. With ammonia, the
intermediate undergoes a further deprotonation step to form
the p-amine.
H
Br → CH3CH2
Include balanced equations for all reactions. Include essential
conditions (e.g. solvent, temperature, sealed tube under
pressure for NH3)
Chemistry for Advanced Level 25.3
Advanced Chemistry 115
AS Level and A Level Chemistry 17.1, 17.5
H
Chemistry for Advanced Level 25.3
Advanced Chemistry 115
AS Level and A Level Chemistry 17.2, 17.3
site 2 (interactive organic mechanisms)
AS Level and A Level Chemistry 17.4
Teaching AS Practical Skills 27
H
recall the chemistry of alcohols, exemplified
by ethanol:
(i) combustion
Most of these reactions can be carried out in the laboratory,
which will help students to remember the necessary
conditions. Provide balanced equations for all reactions (use
Cambridge AS Level Physical Science (8780)
Chemistry for Advanced Level 26.3
Advanced Chemistry 116
AS Level and A Level Chemistry 18a.3
5
Syllabus ref
C15(b)
Learning objectives
Suggested teaching activities
Learning resources
(ii) oxidation to carbonyl compounds and
carboxylic acids
(iii) dehydration to alkenes
[O] for the oxygen atoms provided by the oxidising agent) and
include essential conditions (e.g. reagent, solvent,
temperature).
Teaching AS Practical Skills 28
classify hydroxy compounds into primary,
secondary and tertiary alcohols:
(i) suggest characteristic distinguishing
reactions, e.g. mild oxidation
Revise nomenclature and isomerism. Definition and practice
with recognising primary, secondary and tertiary R-OH.
Molecular models will prove useful.
Primary and secondary alcohols reduce hot acidified
dichromate from orange to green.
If the reaction mixture from the oxidised alcohols is distilled,
the distillate will show an acidic reaction (→ RCO2H) if ROH is
primary, but a neutral reaction if ROH is secondary. (In either
case the distillate could give an orange ppt with 2,4-DNPH,
from an aldehyde or a ketone, so this is not a useful
distinguishing reagent). An alternative method is to test for the
presence (or absence) of the aldehyde, produced by partial
oxidation of the primary alcohol, with Fehling’s or Tollens’
reagent. Practical work is possible here for competent
students.
Tertiary alcohols give no reaction as there is no hydrogen atom
on the carbon atom to which the –OH group is attached.
Chemistry for Advanced Level 26.1-26.2/3
Advanced Chemistry 116
AS Level and A Level Chemistry 18a.4
A good yield of some aldehydes or ketones can be obtained in
a preparative experiment (cyclohexanol to cyclohexanone is
particularly effective, as also is benzoin (C6H5CH(OH)COC6H5)
to benzil). To enhance the production of the aldehyde at the
expense of the acid, the Cr2O72– solution should be dripped
onto the acidified R-OH in a distillation flask which is kept at a
temperature just below the b.pt. of the alcohol. Once formed,
the more volatile aldehyde distils off, so avoiding further
oxidation.
Chemistry for Advanced Level 28.4
Advanced Chemistry 118
AS Level and A Level Chemistry 18a.5
(ii) the resistance of tertiary alcohols to
oxidation using Cr2O72–/H+ explained in
terms of the absence of a hydrogen
atom on the central carbon atom
C15(c)
C15(d)
v2 2Y07
describe the formation of aldehydes and
ketones from primary and secondary
alcohols respectively using Cr2O72–/H+
compare the production of ethanol by
fermentation, and by the catalytic addition
of steam to ethene, in terms of conditions,
rate, purity of product and required
A simple comparison only is required. Students should be
aware of the conditions required for both processes and be
able to compare the two processes in terms of rate (slow/fast),
purity of product (low/high) and technology (low/high) for
Cambridge AS Level Physical Science (8780)
site 4 (alcohols)
site 4 (carbonyls)
site 7 (N-ch3-07, 15)
Chemistry for Advanced Level 26.4
6
Syllabus ref
C15(e)
C15(f)
Learning objectives
Suggested teaching activities
technology
fermentation/catalytid addition routes. Mention should be made
of the renewable/non-renewable aspects of the processes.
describe:
(i) the use of 2,4-dinitrophenylhydrazine
(2,4–DNPH) reagent to detect the
presence of carbonyl compounds
(ii) the reduction of aldehydes and ketones
e.g. using NaBH4
The formation of an orange-yellow ppt. is firm evidence. The
equation for the reaction including the formula of the product
could be given, to interested students, but is not essential.
An experiment reducing benzoin with NaBH4 is easily carried
out and gives a clean yield of a crystalline product
deduce the nature (aldehyde or ketone) of
an unknown carbonyl compound from the
results of simple tests (i.e. Fehling's and
Tollens' reagents; ease of oxidation)
Both tests can be carried out in the laboratory. The identities
of the reduced products (Cu2O and Ag, respectively) should be
known. The equations for their formation are not too difficult
but they are not essential.
Learning resources
Chemistry for Advanced Level 28.3
Advanced Chemistry 118
AS Level and A Level Chemistry 19.3
site 7 (N-ch3-17)
site 21a
Chemistry for Advanced Level 31.4-31.5
Advanced Chemistry 118
AS Level and A Level Chemistry 19.4
Teaching AS Practical Skills 29
site 21a
Practical work could include the categorisation of a few
“unknowns” to the classes of ROH, RCHO or R2CO on the
basis of the reaction with 2,4-DNPH and Tollens’
reagent/Fehling’s solution.
C15(g)
describe the formation of carboxylic acids
from alcohols, aldehydes and nitriles
Oxidation of alcohols or aldehydes with an excess of Na2Cr2O7
+ dil H2SO4. (balanced equations could include [O]).
Chemistry for Advanced Level 29.8
Advanced Chemistry 119
AS Level and A Level Chemistry 20a.1
Hydrolysis of RCN with hot dilute H2SO4. The full balanced
equation, giving NH4+ + RCO2H, is not difficult.
site 4 (carboxylic acids)
C15(h)
describe the reactions of carboxylic acids in
the formation of salts
Titration with NaOH (using phenolphthalein); reaction with
Na2CO3 (→ CO2: a useful test for RCO2H); reaction with Na
metal; - all give RCO2– Na+.
Chemistry for Advanced Level 29.3
Advanced Chemistry 119
AS Level and A Level Chemistry 20a.2
Teaching AS Practical Skills 30
C16(a)
describe the characteristics of addition
polymerisation as exemplified by
poly(ethene) and PVC
Describe the free-radical conditions using O2 + pressure.
Definition of addition polymerisation.
Chemistry for Advanced Level 24.4
Advanced Chemistry 112, 127-8
AS Level and A Level Chemistry 16b.14-16
C16(b)
write equations for the polymerisation of a
given alkene monomer
The repeat unit is merely the alkene moiety with the double
bond replaced by repeating single bonds: poly(propene) is –
site 4 (polymers)
v2 2Y07
Cambridge AS Level Physical Science (8780)
7
Syllabus ref
Learning objectives
Suggested teaching activities
Learning resources
[CH2-CH(CH3)-]-. Practise drawing repeat units of polymers
from various monomers (incl. the “spare” bonds at each end.
AS Level and A Level Chemistry 16b.18-20
For a balanced equation, there should be brackets ( )n around
the repeat unit) and ‘n’ moles of the monomer.
It is easier to ensure that only the C=C bond carbon atoms are
included in the polymer chain if the alkene is drawn with the
C=C bond central and the ‘H’ atoms/attached groups joined
above and below to the atoms in the C=C bond. For an
addition copolymer, both monomers should be included in the
repeat unit.
C16(c)
identify the monomer used in the formation
of a given poly(alkene)
Practise working out the formula of a monomer – draw the
repeat unit, remove the ‘spare’ bonds and complete the C=C
bond. For an addition polymer, the backbone chain should be
broken up into two-carbon units, and a double bond inserted
between the two carbon atoms. Students should be aware
that copolymers will have two (or more) different monomers.
C16(d)
recognise the difficulty of the disposal of
poly(alkene)s, i.e. non-biodegradability and
harmful combustion products.
Branched chain polyalkenes are especially difficult to
biodegrade. Phosgene (COCl2) and dioxins can be formed if
the incineration temperature for PVC is not high enough.
Newer disposal techniques include cracking, to regenerate the
monomer, and very high temperature combustion, giving
useful heat for power generation.
v2 2Y07
Cambridge AS Level Physical Science (8780)
8