Edexcel IAL Chemistry 18.6 phenol bromination and ring activation

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This question assesses a student's ability to show a coherent and logically structured answer with linkages and fully-sustained reasoning.

Marks are awarded for indicative content and for how the answer is structured and shows lines of reasoning.

The following table shows how the marks should be awarded for indicative content.

Number of indicative marking

points seen in answer

Number of marks awarded for

indicative marking points

6

5-4

3-2

1

0

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The following table shows how the marks should be awarded for structure and lines of reasoning.

Comment:

Look for the indicative marking points first, then consider the mark for structure of answer and sustained line of reasoning

Indicative content

- IP1 - Similarity
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Guidance on how the mark scheme should be applied:

The mark for indicative content should be added to the mark for lines of reasoning. For example, an answer with five indicative marking points that is partially structured with some linkages and lines of reasoning scores 4 marks ( 3 marks for indicative content and 1 mark for partial structure and some linkages and lines of reasoning).

If there are no linkages between points, the same five indicative marking points would yield an overall score of 3 marks (3 marks for indicative content and no marks for linkages).

In general it would be expected that 5 or 6 indicative points would get 2 reasoning marks, and 3 or 4 indicative points would get 1 mark for reasoning, and 0,1 or 2 indicative points would score zero marks for reasoning.

General points to note

If there is any incorrect chemistry, deduct mark(s) from the reasoning. If no reasoning mark(s) awarded do not deduct mark(s).

Accept structures for names throughout If name and formula given both must be correct

Deduct a reasoning mark if there is no comparison given for IP1 to IP3

Do not penalise unbalanced / incomplete equations Deduct (mark) from reasoning if any products given are incorrect

(6)

All are attacked by / react with electrophiles

- IP2 - Types of reaction

Cyclohexene undergoes addition reactions but benzene and/or phenol undergo substitution reactions

- IP3 - Conditions

Cyclohexene and/or phenol react with (aqueous) bromine / without a catalyst and benzene needs

(a Friedel-Crafts catalyst / iron / iron(III) bromide)

- IP4 - Benzene

Benzene has delocalised electrons and is (kinetically) stable so the reaction has a high activation energy

- IP5 - Cyclohexene

Cyclohexene has localised electron density in one $\pi$ bond (which increases the electron density and makes it more susceptible to electrophilic attack)

- IP6 - Phenol

Phenol has a lone pair of electrons on the oxygen which is delocalised (within the ring)

and

makes it more susceptible to electrophilic attack

All three need to be mentioned for this IP - evidence for
phenol reacting with an electrophile may be seen in IP6
Accept benzene forms monobromo product /
bromobenzene, cyclohexene forms dibromo product / 1,2-
dibromocyclohexane and phenol forms tribromo product /
2, 4, 6-tribromophenol
Allow HBr is produced with benzene and phenol but
cyclohexene only forms one product
Allow react under normal laboratory conditions / room
temperature and pressure
Allow reference to $\mathrm{AlBr}_{3} / \mathrm{AlCl}_{3}$
This IP can be awarded if benzene equation has catalyst and
other equation(s) do not
Ignore references to specific temperatures
Allow delocalised ( $\pi$ ) electron ring in benzene is (very)
stable
Allow delocalisation of electrons in $\pi$ bonds which
decreases the electron density (of the ring) and makes it less
susceptible to electrophilic attack
If neither IP4 or IP5 awarded then allow (1) for benzene has
delocalised electrons but cyclohexene does not
Allow the lone pair (of electrons) on the oxygen/OH in
phenol
and increases the electron density of the (benzene)
ring/overlaps with the delocalised ring