A-LevelChemistryHydrocarbons9701/42 · Feb/Mar 2023 · Q522 Marks

Tulobuterol is used in some medicines. tulobuterol Cl OH H N [Figure 5.1]

(a)Tulobuterol contains a benzene ring in its structure. Describe and explain the shape of benzene. In your answer, include: • the bond angle between carbon atoms • the hybridisation of the carbon atoms • how orbital overlap forms σ and π bonds between the carbon atoms.[3]
(b)(i)Write an equation to show how Cl2 reacts with AlCl3 to generate an electrophile.[1]
(b)(ii)Complete the mechanism in Fig. 5.3 for the reaction of benzene with the electrophile generated in (b)(i). Include all relevant curly arrows and charges. Draw the structure of the intermediate. [Figure 5.3][3]
(c)(i)Name the mechanism of the reaction in step 2.[1]
(c)(ii)Draw the structure of an isomer of Q that forms as an organic by-product of the reaction in step 2.[1]
(c)(iii)The reactants used in step 2 contain acyl chloride, alkyl chloride and aryl chloride functional groups. State and explain the relative ease of hydrolysis of acyl chlorides, alkyl chlorides and aryl chlorides. easiest to hydrolyse .............................................. hardest to hydrolyse[3]
(d)Tulobuterol is produced from Q as shown in Fig. 5.5. Suggest reagents and conditions for steps 3 and 4. Draw the structure of Z in the box. step 3 .............................................. step 4 .............................................. [Box for Z][3]
(e)(i)Define enantiomers.[1]
(e)(ii)Suggest one disadvantage of producing two enantiomers in this synthesis.[1]
(e)(iii)Suggest a method of adapting the synthesis to produce a single enantiomer.[1]
(f)(i)Predict the number of peaks that would be seen in the carbon-13 NMR spectrum of tulobuterol.[1]
(f)(ii)The peak for the —CH2N— environment is a doublet in the chemical shift range δ = 2.0–3.0 ppm. Give details for each of the other three peaks in the proton NMR spectrum of tulobuterol, to include: • chemical shift • environment of the proton • splitting pattern • number of ¹H atoms responsible. Table 5.1 gives information about typical chemical shift values.[3]

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 (Feb/Mar 2023). The mark or mark type is shown in brackets.

[1] bond angle = 120° AND shape is hexagonal ring planar/trigonal planar
[1] (carbons are) sp² hybridised
[1] contains delocalised electrons in the π bonds / system
[1] (sp² orbitals) overlap end-on-end/ head-on to form σ bonds
[1] a p orbital (from each carbon atom) overlaps sideways (with each other above and below the ring) forming π bonds any three
[1] Cl2 + AlCl3 → Cl⁺ + AlCl4⁻
[1] M1 curly arrow from inside hexagon of aromatic ring to Cl⁺ CON going to a lone pair on Cl
[1] M2 intermediate
[1] M3 curly arrow from C—H bond to inside the ring AND H⁺
[1] electrophilic substitution
[1] OR 4-substituted acyl / alkyl derivative [structure of para isomer] ALLOW 3-substituted acyl / alkyl derivative [structure of meta isomer]
[1] (most) acyl chloride > alkyl chloride > aryl chloride (least)
[1] any two from: acyl chlorides: carbon (in C—Cl) is more electron deficient AND it is also attached to an oxygen atom / two electronegative atoms OR C-Cl bond is weakest / weakened in acyl chlorides AND it is also attached to an oxygen atom / two electronegative atoms
[1] aryl chlorides (no hydrolysis) C—Cl bond is part of delocalised system / partially double bond character so C-Cl bond is stronger OR lone pair on Cl delocalises with π ring so C-Cl bond is stronger
[1] alkyl chlorides carbon atom has a smaller δ+ AND due to the carbon being only attached to one electronegative atom OR C-Cl bond strengthened AND by electron donating effect / positive inductive effect of alkyl / R group
[1] (CH3)3CNH2 (in ethanol) [substitution] } in either order
[1] LiAlH4 OR NaBH4 [reduction] } in either order
[1] Cl OH HN Cl [structure for Z]
[1] rotate the plane of polarised light in the opposite direction OR stereoisomers / molecules that are non-superimposable mirror images
[1] need to separate the optical isomers to form the pure active isomer OR reduced / different biological activity of ‘other' enantiomer OR lower yield of biologically active molecule / desired molecule
[1] chiral catalyst OR use of an enzyme
[1] ten/10
[1] (δ = 0.9-1.7) • 9H • singlet • -CH3/alkane
[1] (δ = 3.2-4.0)/ (δ = 2.3-3.0) • 1H • triplet • –CHO / alkyl next to electronegative atom OR Ar-CH/alkyl next to aromatic ring
[1] (δ = 6.0-9.0) • 4H • multiplet • H-Ar/attached to aromatic ring any three [1] any six [2] all nine [3]