A-LevelChemistryAnalytical techniques9701/42 · May/June 2022 · Q78 Marks

State the uses of TMS and D₂O in NMR spectroscopy.

(a)State the uses of TMS and D₂O in NMR spectroscopy.[1]
(b)(i)The three isomeric ketones with molecular formula C5H10O are: • pentan-2-one • pentan-3-one • 3-methylbutanone. Complete Table 7.1 to show the number of peaks observed in the proton (1H) NMR spectrum and in the carbon-13 NMR spectrum for each compound listed. [Figure Table 7.1][2]
(b)(ii)State all the ketones with molecular formula C5H10O that have: a doublet in their proton (1H) NMR spectrum a singlet in their proton (1H) NMR spectrum.[2]
(c)(i)Cortisone, C21H28O5, is a naturally occurring chemical that contains chiral carbon atoms. [Figure cortisone, Fig. 7.1] Deduce the number of chiral carbon atoms in one molecule of cortisone.[1]
(c)(ii)Cortisone is reacted with an excess of NaBH4. State the molecular formula of the organic compound formed.[1]
(c)(iii)Cortisone is an optically active molecule. Explain what is meant by optically active.[1]

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Mark scheme

Marking points from the official mark scheme (May/June 2022). The mark or mark type is shown in brackets.

[1] (TMS) reference OR standard OR to define d = 0
[1] (D2O) solvent OR identification of O-H / N-H protons / group
[2] [Table values for ketone: pentan-2-one 1H:4 13C:5; pentan-3-one 1H:2 13C:3; 3-methylbutanone 1H:3 13C:4] three for one mark, six for two marks
[2] M1 3-methylbutanone
[2] M2 3-methylbutanone AND pentan-2-one
[1] six / 6
[1] C21H34O5
[1] a substance that is able to rotate the plane of polarised light in opposite directions

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