A-LevelChemistryOrganic synthesis9701/23 · Oct/Nov 2025 · Q416 Marks

[Figure 4.1] shows a possible synthesis of propene, C₃H₆.

(a)(i)Identify the type of reaction that occurs in reaction 1. [1][1]
(a)(ii)Suggest a suitable reagent for reaction 2. [1][1]
(a)(iii)Reaction 3 is an elimination reaction. Write an equation for this reaction and identify the solvent and conditions used. equation .................................................................................................................................. solvent and conditions ............................................................................................................ [2][2]
(a)(iv)C₂H₅CH₂OH can be directly converted to C₃H₆. Suggest the reagent and conditions for this conversion. [1][1]
(b)(i)Under suitable conditions, propene polymerises to form poly(propene). Poly(propene) exhibits stereoisomerism. Identify the type of polymerisation that forms poly(propene) from propene. [1][1]
(b)(ii)Define stereoisomerism. [2][2]
(b)(iii)Draw a section of poly(propene), showing two repeat units. Use your diagram to identify the type of stereoisomerism shown by poly(propene). Explain your answer. section of poly(propene) [diagram space] [3][3]
(b)(iv)State two difficulties associated with the disposal of poly(propene). 1 ................................................................................................................................................ 2 ................................................................................................................................................ [2][2]
(c)(i)Under different conditions, two molecules of propene can combine to form compounds X and Y. [Structures of X and Y] Name X. [1][1]
(c)(ii)[Figure 4.2] shows the mass spectrum of either compound X or compound Y. Identify which of X and Y gives this mass spectrum. Give one reason for your answer, referring to the fragmentation pattern. [1][1]
(c)(iii)The molecular ion peak in the spectrum in [Figure 4.2] has relative abundance 34.7. Calculate the relative abundance of the [M+1]⁺ peak in this spectrum. relative abundance of [M+1]⁺ peak = ............................................................ [1][1]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2025). The mark or mark type is shown in brackets.

[1] reduction
[1] PCl5 / PCl3 / SOCl2 OR KCl / NaCl AND conc. H2SO4 / conc. H3PO4
[2] M1 C2H5CH2Cl + NaOH → C3H6 + H2O + NaCl
M2 ethanol (solvent) AND heat / reflux
[1] conc. H2SO4 OR conc. H3PO4 OR Al2O3 AND heat
[1] addition
[2] M1 (molecules that have the) same structural formula (and same molecular formula)
M2 but different 3D / spatial arrangement of atoms / groups
[3] M1 [Diagram of two repeat units of poly(propene) like H CH3 H CH3 / -C-C-C-C- / H H H H]
M2 optical isomerism
M3 the methylated carbon has four different groups attached
[2] M1 non-biodegradability
M2 harmful combustion products
[1] 2,3-dimethylbut-1-ene
[1] (The spectrum is of) X AND
41 is [CH2=CCH3]+/41 is C3H5+
OR 43 is [CH3CHCH3]+/43 is C3H7+
OR X would NOT have significant peak at 54 / [(CH3)2C=C+] / C4H6+
OR X would NOT have significant peak at 42 due to [(CH3)2C+] / C3H6+
[1] ([M+1]+/ 34.7 × 100 / 1.1 = 6)
[M+1]+ = 2.29