A-LevelChemistryOrganic synthesis9701/41 · Oct/Nov 2025 · Q813 Marks

In the electrophilic substitution of arenes, different substituents can direct to different ring positions. Describe the directing effect of the –NO2 group. Explain your answer.

(a)(i)In the electrophilic substitution of arenes, different substituents can direct to different ring positions. Describe the directing effect of the –NO2 group. Explain your answer.[1]
(a)(ii)The nitration of arenes uses a mixture of concentrated HNO3 and concentrated H2SO4 to generate the NO2+ electrophile. Write an equation for the formation of the NO2+ electrophile.[1]
(b)(i)Carbon-carbon bond formation is an important reaction in organic synthesis. Fig. 8.1 shows the synthesis of compound Q from benzene in two reaction steps. [Figure 8.1] Draw the structure of compound P in the box in Fig. 8.1.[1]
(b)(ii)Suggest reagents and conditions for reactions 1 and 2 in Fig. 8.1. reaction 1 _________________________ reaction 2 _________________________ [2][2]
(c)Separate samples of C6H5Br and C6H5CH2Br are added to warm AgNO3(aq). State the expected observations, if any. Explain your answer. C6H5Br with AgNO3(aq) ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ C6H5CH2Br with AgNO3(aq) ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ explanation ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ [3][3]
(d)(i)Acyl bromides, RCOBr, react readily with H2O. The mechanism of this reaction is similar to that of the reaction of H2O with acyl chlorides, RCOCl. Name the mechanism of this reaction.[1]
(d)(ii)Complete the mechanism in Fig. 8.2 for the reaction of RCOBr with H2O. Include all relevant lone pairs of electrons, curly arrows, charges and dipoles. Draw the structure of the intermediate. [Figure 8.2 to complete] [4][4]

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] NO2 group directs to 3 (and 5) / meta position AND due to being an electron-withdrawing / electronegative group
[1] HNO3 + H2SO4 → NO2+ + HSO4¯ + H2O OR HNO3 + 2H2SO4 → NO2+ + 2HSO4¯ + H3O+
[1] (structure of P: acetophenone, C6H5COCH3)
[1] M1: (reaction 1) ethanoyl chloride / CH3COCl AND AlCl3
[1] M2: (reaction 2) 2-bromopropane / (CH3)2CHBr AND FeBr3
[1] M1: with C6H5Br no change / no precipitate AND with C6H5CH2Br cream precipitate
[1] M2: in C6H5Br lone pair / p-orbital on Br delocalised / overlaps with ring / π system
[1] M3: C-Br bond stronger / has partially double bond character
[1] (nucleophilic) addition-elimination
[1] M1 M2: lone pair on O
[1] M1 M2: curly arrow from (lone pair) O (in H2O) to C (of C=O)
[1] M1 M2: correct dipole on C=O
[1] M1 M2: curly arrow from the C=O bond to O atom
[any two [1], all four [2]]
[1] M3: correct intermediate
[1] M4: curly arrow from (lone pair on) O(-) to C–O bond AND curly arrow from C-Br to Br