| Date | May 2019 | Marks available | 2 | Reference code | 19M.3.hl.TZ2.25 |
| Level | HL | Paper | 3 | Time zone | TZ2 |
| Command term | Outline | Question number | 25 | Adapted from | N/A |
Question
Taxol is a drug that was once obtained from yew trees and is now produced using chiral auxiliaries.
Examine the synthesis of taxol in terms of green chemistry criteria.
Outline the operation of a polarimeter used to distinguish between enantiomers.
Markscheme
Any two of:
produced by genetically engineered/modified bacteria/E. coli
OR
sustainable because synthesized and not obtained from yew trees [✔]
chiral auxiliaries «isolated and» reused [✔]
one enantiomer produced [✔]
toxicity/recycling of solvents/materials used [✔]
overall yield/atom economy/waste generated [✔]
Any two of:
«plane-» polarized light
OR
light passes through polarizer/polarizing filter [✔]
enantiomers rotate plane of «plane-» polarized light «by equal angles» in opposite directions [✔]
measure angle/direction of rotation [✔]
Examiners report
The synthesis of taxol in terms of green chemistry criteria invited varied responses. While some candidates were precise in their answers but others lost focus and wrote something about green chemistry.
The operation of a polarimeter to distinguish between enantiomers was generally well handled by the candidates while some missed stating to measure the angle/direction of rotation.
Syllabus sections
- 16N.3.hl.TZ0.26c: Omeprazole exists as a racemic mixture whereas esomeprazole is a single enantiomer. Outline...
- 18N.3.hl.TZ0.21c: Explain the process of solvent extraction by which Taxol is isolated.
- 18N.3.hl.TZ0.21b: Outline how chiral auxiliaries are used to synthesize the desired enantiomer.
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17M.3.hl.TZ1.28b:
A mixture of enantiomers shows optical rotation.
Suggest a conclusion you can draw from this data.
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19M.3.hl.TZ1.25a:
Identify the chiral carbon atom using an asterisk, *.
-
17N.3.hl.TZ0.23b:
Explain the role of the chiral auxiliary in the synthesis of Taxol.
- 19N.3.hl.TZ0.26a: State the feature of Taxol that is a major challenge in its synthesis. Use section 37 of the...
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19M.3.hl.TZ1.25b:
Enantiomers can be identified using a polarimeter. Outline how this instrument differentiates the enantiomers.
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18N.3.hl.TZ0.21a:
The diagram shows part of a Taxol molecule in skeletal form.
Draw a circle around each chiral carbon.
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18M.3.hl.TZ1.16e:
Many drugs are chiral. Explain how a polarimeter can be used to determine the relative proportion of two enantiomers.
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18M.3.hl.TZ2.25:
Taxol was originally obtained from the bark of the Pacific yew tree.
Outline how Green Chemistry has improved the process of obtaining Taxol.
-
19N.3.hl.TZ0.26b:
Describe how the challenge in (a) was resolved by pharmaceutical companies.
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17M.3.hl.TZ2.25:
Taxol is produced using a chiral auxiliary. Describe how the chiral auxiliary functions to produce the desired product.
- 20N.3.hl.TZ0.19d: Circle two chiral carbons in the section of the Taxol structure below.
