| Date | November 2016 | Marks available | 2 | Reference code | 16N.3.hl.TZ0.26 |
| Level | HL | Paper | 3 | Time zone | TZ0 |
| Command term | Outline | Question number | 26 | Adapted from | N/A |
Question
Excess stomach acid leads to medical conditions that affect many people worldwide. These conditions can be treated with several types of medical drugs.
Omeprazole exists as a racemic mixture whereas esomeprazole is a single enantiomer. Outline how, starting from a non-chiral molecule, esomeprazole but not omeprazole, could be synthesized. Details of chemicals and conditions are not required.
Markscheme
Any two of:
chiral molecule/auxiliary/optically active species is used/added/connected «to the starting molecule to force reaction to follow a certain path»
chiral intermediate forms «only» one enantiomer
OR
auxiliary creates stereochemical condition «necessary to follow a certain pathway» / stereochemical induction
OR
existing chiral centre affects configuration of new chiral centres
«after new chiral centre created» chiral auxiliary removed «to obtain desired product»
Examiners report
Syllabus sections
- 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, *.
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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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19M.3.hl.TZ2.25b:
Outline the operation of a polarimeter used to distinguish between 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.
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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.
