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Date November 2020 Marks available 2 Reference code 20N.3.hl.TZ0.19
Level HL Paper 3 Time zone TZ0
Command term Explain Question number 19 Adapted from N/A

Question

Consider the structures of medicinal molecules in section 37 of the data booklet.

Explain how zanamivir works as a preventative agent against flu viruses.

[2]
a.

Circle the side-chain in penicillin on the structure below.

[1]
b(i).

Explain, with reference to the action of penicillin, why new penicillins with different side-chains need to be produced.

 

[2]
b(ii).

State and explain the relative solubility of codeine in water compared to morphine and diamorphine.

[2]
c(i).

State the natural source from which codeine, morphine and diamorphine are obtained. 

[1]
c(ii).

Circle two chiral carbons in the section of the Taxol structure below.

[1]
d.

Markscheme

«drug» blocks/inhibits «viral» enzyme/neuraminidase/NA «activity» ✔

prevents virus from leaving/escaping host cells «thus cannot infect other cells» ✔


Do not accept other anti-viral methods (as question is specific to Zanamivir).

a.

   ✔

Accept a circle that does not surround the amido group.

Do not accept a circle that only surrounds the phenol group.

b(i).

bacterial resistance «to older penicillins/antibiotics» ✔

prevent penicillinase/beta-lactamase/enzyme in bacterium to deactivate/open penicillin/beta-lactam ring ✔


Accept “antibiotic resistant bacteria” but not “antibiotic resistance” for M1.

Accept “reduce allergic reactions from penicillin” for M2.

Award [1 max] for “increased efficiency” OR “increased stability in GIT”.

Do not accept “bacteria develop tolerance”.

b(ii).

codeine less soluble «in water» than morphine AND more soluble than diamorphine
OR
morphine > codeine > diamorphine «in terms of solubility in water» ✔

more/stronger/greater hydrogen/H bonding «due to more hydroxyl groups leads to greater solubility» ✔

c(i).

opium poppy/plants/seeds ✔

Accept “poppy” OR “opioid”.

c(ii).

any two chiral carbons identified ✔

d.

Examiners report

In this question candidates were required to describe how the mixture can be separated by fractional distillation. Only the better candidates scored both marks, though most gained at least one mark, usually for stating that the most volatile component is collected first. Many did not convey the idea that there is continuous evaporation and condensation in the process or the fact that the temperature decreases up the fractionating column.

a.

Most were able to circle the side-chain in penicillin. Common errors included circling only the phenolic group, the four-membered ring or the five-membered ring.

b(i).

This question was well answered though many lost M1 for stating "antibiotic resistance" instead of mentioning "bacterial resistance".

b(ii).

Only the better candidates were able to state and explain the relative solubility of codeine in water compared to morphine and diamorphine. The majority scored M1 for the correct order of relative solubility. Few gave a comprehensive explanation outlining that there is greater hydrogen bonding due to more hydroxyl groups, which results in greater solubility.

c(i).

The natural source from which codeine, morphine and diamorphine are obtained had to be stated. Most scored the single mark here for "poppy". Common errors included "willow tree" or "opium" alone, which was not deemed sufficient to score the mark.

c(ii).

The idea of a chiral carbon was very well understood and nearly all scored the mark for identifying any two chiral carbons in Taxol.

d.

Syllabus sections

Options » D: Medicinal chemistry » D.2 Aspirin and penicillin
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