A-LevelChemistryHydrocarbons9701/42 · Oct/Nov 2020 · Q720 Marks

Describe the structure of a benzene molecule, C6H6. Your answer should include: • the shape of the molecule • the relative lengths of the C-C bonds • bond angles • the hybridisation of the carbon atoms • the overlap between orbitals that produces each type of bond present.

(a)Describe the structure of a benzene molecule, C6H6. Your answer should include: • the shape of the molecule • the relative lengths of the C-C bonds • bond angles • the hybridisation of the carbon atoms • the overlap between orbitals that produces each type of bond present.[4]
(b)Benzene can be used as a starting material to produce phenylamine by a two-step synthesis. benzene ---step 1---> nitrobenzene ---step 2---> phenylamine [Figure 7.1]
(b)(i)Step 1 is the reaction of benzene with NO2+ ions. Complete the mechanism and draw the intermediate of step 1. Include all relevant charges and curly arrows to show the movement of electron pairs. [Figure 7.2][2]
(b)(ii)State the name of the mechanism in (b)(i).[1]
(b)(iii)Identify the reagents needed to produce NO2+ ions. Write an equation to explain how these reagents produce NO2+ ions.[2]
(b)(iv)Give reagents and conditions for the production of phenylamine from nitrobenzene in step 2.[2]
(c)Phenylamine reacts with Br2(aq).
(c)(i)Write an equation for this reaction. You may use structural or displayed formulae.[1]
(c)(ii)Name the organic product of this reaction.[1]
(c)(iii)Describe two observations that can be seen when phenylamine reacts with Br2(aq). observation 1 observation 2[1]
(d)Describe the relative basicities of ammonia, ethylamine and phenylamine, starting with the least basic. Explain your answer in terms of their structures. least basic < < most basic[3]
(e)1,3-diaminopropane, H2NCH2CH2CH2NH2, can be used to make polyamides.
(e)(i)Identify one compound that would react with 1,3-diaminopropane to form a polyamide.[1]
(e)(ii)Draw a section of the polymer chain formed from 1,3-diaminopropane and the compound you chose in (e)(i). Your answer should: • include four monomer residues (two of each type of monomer) • show the amide link fully displayed • clearly identify one repeat unit of this polymer.[2]

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 2020). The mark or mark type is shown in brackets.

[1] (regular) hexagon OR planar
[1] all C-C bonds same length
[1] all bond angles 120°
[1] all carbon atoms sp² hybridised
[1] C-H bonds are s-sp² overlap
[1] C-C bonds have sp²-sp² overlap
[1] C-C bonds have p-p overlap
[1] π used correctly and σ used correctly once each
[1] curly arrow from within hexagon towards NO2+
[1] AND curly arrow from C–H bond to within hexagon
[1] intermediate
[1] electrophilic substitution
[1] conc nitric acid and sulfuric acid
[1] HNO3 + 2H2SO4 → NO2+ + H3O+ + 2HSO4- OR
[1] HNO3 + H2SO4 → NO2+ + H3O+ + SO42- OR
[1] 2HNO3 + H2SO4 → 2NO2+ + H2O + SO42- OR
[1] HNO3 + H2SO4 → NO2+ + H2O + HSO4-
[1] tin and HCl
[1] conc and heat / boil / reflux
[1] C6H5NH2 + 3Br2 → C6H2Br3NH2 + 3HBr
[1] 2,4,6-tribromophenylamine
[1] decolourisation of bromine AND white precipitate
[1] phenylamine < ammonia < ethylamine
[1] lp on nitrogen of phenylamine delocalised into ring
[1] alkyl group of ethylamine electron donating / has positive inductive effect
[1] correct statement about availability of lone pair to accept proton once
[1] either a dioic acid or a dioyl chloride
[1] trailing bonds
[1] two of each monomer residue, consistent with ei
[1] repeat unit identified
[1] amide link showing C=O