DP Chemistry (last assessment 2024)

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Question 19M.3.hl.TZ2.12b

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Date May 2019 Marks available [Maximum mark: 1] Reference code 19M.3.hl.TZ2.12b
Level hl Paper 3 Time zone TZ2
Command term Classify Question number b Adapted from N/A
b.
[Maximum mark: 1]
19M.3.hl.TZ2.12b

Sucrose is a disaccharide.

(b)

Classify, giving your reason, the hexose (six-membered) ring of sucrose as an α or β isomer.

[1]

Markscheme

α-isomer AND hydroxyl group on carbon 1 and –CH2OH are trans
OR
α-isomer AND hydroxyl group on carbon 1 is below plane of ring
OR
α-isomer AND glycosidic linkage between rings is below plane of ring  [✔]

 

Note: Accept “ether linkage” for M3.

Examiners report

This part was very poorly answered. Majority of the candidates had no idea about the reason whether the six-membered ring was an alpha or beta isomer.

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