Covering Lessons 11 to 15: drug classification, functional groups, acid-base properties, chirality, drug delivery, aspirin synthesis and green chemistry. Use this checkpoint to test whether you can connect molecular structure to drug action, formulation and synthesis decisions.
Which functional group is represented by -CONH-?
For a weak acid, what happens when pH is greater than pKa?
What is a racemic mixture?
Why might a transdermal patch be preferred over an oral tablet for some drugs?
Which pair of reagents is used in aspirin synthesis?
Which statement about atom economy is correct?
What does a pharmacophore describe?
Which statement best explains why one enantiomer can be therapeutic while another is harmful?
What is first-pass metabolism?
Which statement best describes polarimetry?
Explain how the ionisation state of a weakly acidic drug affects its membrane permeability and aqueous solubility. 4 marks
Explain why modern drug development prefers enantiopure drugs rather than racemic mixtures, using thalidomide as an example. 4 marks
Evaluate the sustainability of an aspirin synthesis route using atom economy, E-factor and the role of catalysts. In your answer, explain why successful product formation alone is not enough to judge the route. 5 marks
1. C — -CONH- is the amide functional group.
2. A — when pH is above pKa for a weak acid, A- is favoured.
3. D — a racemic mixture is a 50:50 mixture of enantiomers.
4. B — a transdermal patch can bypass first-pass metabolism and provide steadier delivery.
5. C — aspirin is synthesised from salicylic acid and acetic anhydride.
6. A — atom economy measures how much product-side atom mass appears in the desired product.
7. B — a pharmacophore is the key activity-producing feature set in the molecule.
8. D — chiral biological targets can distinguish enantiomers.
9. C — first-pass metabolism occurs before a swallowed drug fully reaches general circulation.
10. A — polarimetry detects optical activity through rotation of plane-polarised light.
Q11 (4 marks): For a weakly acidic drug, the unionised form HA is generally less polar and crosses lipid membranes more easily. The ionised form A- is charged and usually more soluble in aqueous environments, but it crosses hydrophobic membranes less readily. This means ionisation state changes the balance between solubility in body fluids and membrane permeability.
Q12 (4 marks): Modern drug development prefers enantiopure drugs because different enantiomers can have different biological effects even though they have the same connectivity. Biological receptors are chiral and can distinguish between mirror-image forms. The thalidomide case shows why this matters: in the course framing, one enantiomer was associated with sedative effects while the other was teratogenic. A racemic mixture therefore created major risk because it contained both forms.
Q13 (5 marks): Successful product formation is not enough to judge a synthesis route because sustainability depends on how efficiently materials are used and how much waste is produced. Atom economy shows the fraction of product-side atom mass that appears in the desired product, so a higher value is better. E-factor shows the mass of waste produced per mass of product, so a lower value is better. A catalyst can improve sustainability by increasing rate and selectivity and reducing wasted reagents or energy demand, even though it is not consumed overall. A good evaluation therefore considers desired product formation, atom use, waste burden and the role of process design together.
Tick when you've finished the review and checked your answers.