| Date | May 2019 | Marks available | 1 | Reference code | 19M.3.hl.TZ1.25 |
| Level | HL | Paper | 3 | Time zone | TZ1 |
| Command term | Identify | Question number | 25 | Adapted from | N/A |
Question
Methadone is a synthetic opiate administered as a racemic mixture to treat strong pain and morphine or heroin dependence.
Identify the chiral carbon atom using an asterisk, *.
Enantiomers can be identified using a polarimeter. Outline how this instrument differentiates the enantiomers.
Markscheme
[✔]
«plane-»polarized light passed through sample [✔]
analyser/second polarizer determines angle of rotation of plane of plane-polarized light
OR
each enantiomer rotates plane «of plane-polarized light» in opposite directions «by the same angle» [✔]
Examiners report
Some candidates had difficulty identifying the chiral carbon in a methadone structure, with quite a few varied answers. However, many managed to mark the correct carbon.
Very poorly answered. Few scored any marks at all when outlining how a polarimeter can be used to differentiate between enantiomers. Many referred to the light or the enantiomers themselves being rotated.
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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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.
