| Date | May 2013 | Marks available | 3 | Reference code | 13M.3.hl.TZ1.D3 |
| Level | HL | Paper | 3 | Time zone | TZ1 |
| Command term | Explain | Question number | D3 | Adapted from | N/A |
Question
Many factors can be involved in the action of a particular drug.
The structures of morphine and diamorphine (heroin) are given in Table 20 of the Data Booklet. With reference to the structures, explain why diamorphine (heroin) is more potent than morphine.
Markscheme
two (polar) hydroxyl groups/OHs in morphine replaced by ester groups in diamorphine;
Do not allow hydroxide for hydroxyl.
Accept two alcohols instead of hydroxyl.
diamorphine less polar / morphine more polar;
diamorphine capable of rapid penetration of (lipid-based) blood-brain barrier / diamorphine more quickly absorbed into non-polar environment of central nervous system/CNS / OWTTE;
Allow diamorphine more soluble/easily dissolved in lipids/fatty tissue.
Examiners report
In contrast (b) was very well answered by nearly all students and several got all three marks.
