A-LevelChemistryOrganic synthesis9701/43 · May/June 2018 · Q86 Marks

Abscisic acid, C15H20O4, is a plant hormone. [Figure showing structure of abscisic acid]

(a)On the diagram of abscisic acid, use an asterisk (*) to label each chiral carbon atom.[1]
(b)Abscisic acid is reacted with an excess of NaBH4. Give the molecular formula of the organic product formed.[1]
(c)(i)Draw the skeletal formula of the carbon-containing product with the largest molecular mass.[1]
(c)(ii)Identify the carbon-containing product with the smallest molecular mass. Explain how this product arises.[2]
(c)(iii)Identify the third carbon-containing product of this reaction by giving its displayed or structural formula.[1]

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Mark scheme

Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.

[1] correct chiral centre labelled only
[1] C15H22O4
[1] (Skeletal formula of product with largest molecular mass - 3-hydroxy-3-methylglutaric acid)
[1] CO2
[1] oxidation / oxidative cleavage
[1] CH3COCO2H

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Topic: Organic synthesis, A-Level Chemistry (syllabus 9701). Structured question, 6 marks.
Source: A-Level Chemistry, May/June 2018 Paper 4 Variant 3, question 8.

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