(CH₃)₃CCHO is used in the synthesis of some antibiotics.

1. (a)(i)Give the name of (CH₃)₃CCHO.[1]
2. (a)(ii)State the hybridisation of the carbon atom labelled with an asterisk, *. [Figure showing H₃C-C(CH₃)₂-C*HO][1]
3. (b)(i)Two reaction sequences are shown. [Figure showing reaction scheme with (CH₃)₃CCHO, NaBH₄, S, [O], A, T, U] Reaction 1 is an oxidation reaction. Identify the reagent(s) and conditions for reaction 1.[1]
4. (b)(ii)A, (CH₃)₃CCO₂H, is a solid at room temperature. B, CH₃CO₂(CH₂)₂CH₃, is an isomer of A. B is a liquid at room temperature. Explain the difference in the physical states of A and B, with reference to any intermolecular forces that may exist.[3]
5. (b)(iii)Give the balanced equation for the reaction of (CH₃)₃CCHO with NaBH₄ to form S. Use [H] to represent an atom of hydrogen provided by NaBH₄.[1]
6. (b)(iv)Draw the structure of the organic molecule T that reacts with A, (CH₃)₃CCO₂H, in reaction 2, to form U. Suggest a catalyst for reaction 2. [Box for drawing T] catalyst[2]
7. (c)(i)X, Y and Z are all isomers of (CH₃)₃CCHO. A summary of some of the reactions and properties of X, Y and Z is shown in the table. | compound | observations with 2,4-DNPH | observations with Fehling's solution | principal absorptions in infra-red spectrum | |---|---|---|---| | X | | no reaction | 1715cm⁻¹ | | Y | | red precipitate | 1730 cm⁻¹ | | Z | no reaction | no reaction | 3200-3600 cm⁻¹; 1630 cm⁻¹; 1050 cm⁻¹ | X and Y each contains a carbonyl group. Complete the table with the expected observations for the reactions of X and Y with 2,4-DNPH.[1]
8. (c)(ii)Identify the functional group present in Y that causes the recorded observation with Fehling's solution.[1]
9. (c)(iii)Y has a chiral centre and exists as a pair of optical isomers. State what is meant by the term chiral centre.[1]
10. (c)(iv)Draw the optical isomers of Y using the conventional three-dimensional representation. [Boxes for drawing isomers][2]
11. (c)(v)Z, C₅H₁₀O, has a branched carbon chain. It shows geometrical isomerism. Complete the table with the bond responsible for each of the principal absorptions seen in the infra-red spectrum of Z. | principal absorptions in infra-red spectrum | bond responsible | |---|---| | 3200-3600 cm⁻¹ | | | 1630 cm⁻¹ | | | 1050 cm⁻¹ | |[1]
12. (c)(vi)Draw the skeletal formula of Z.[3]
13. (c)(vii)X contains a carbonyl group. X reacts with HCN, in the presence of a small amount of NaCN, to form (C₂H₅)₂C(OH)CN as shown. X + HCN → (C₂H₅)₂C(OH)CN Draw the mechanism of the reaction of X with HCN. • Draw the structure of X and the intermediate. • Include all charges, partial charges, lone pairs and curly arrows. [Space for drawing mechanism][3]
14. (c)(viii)State the role of NaCN in the reaction in (c)(vii).[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.