Valinol can be synthesised by the following reactions. Reaction 1 uses valine as the starting material. [Figure 6.1]

1. (a)(i)Write an equation for reaction 1, using [H] to represent the reducing agent.[1]
2. (a)(ii)Suggest a suitable reagent for reaction 1.[1]
3. (a)(iii)Name the mechanism for reaction 2.[1]
4. (b)Valine and glycine, H₂NCH₂COOH, form the tripeptide Gly-Val-Gly. Draw the structure of this tripeptide. Show the peptide bonds fully displayed.[2]
5. (c)(i)Valine exists as two stereoisomers. Draw three-dimensional diagrams to show the two stereoisomers of valine. In your diagrams, the –CH(CH₃)₂ group can be represented by -R. State the type of stereoisomerism shown. type of stereoisomerism[2]
6. (c)(ii)Valine is an amino acid. Draw the zwitterion of valine.[1]
7. (c)(iii)Valinate, Val⁻, is the anion of valine. It takes part in a ligand substitution reaction with hexaaquanickel(II) ions. Complex Z is formed. [Ni(H₂O)₆]²⁺(aq) + 2Val⁻(aq) ⇌ [Ni(H₂O)₂(Val)₂](aq) + 4H₂O(l) Write an expression for Kstab for this equilibrium. Kstab =[1]
8. (c)(iv)At room temperature, the numerical value of Kstab is 2.34 × 10⁵. Explain what this value indicates about the equilibrium and the stability of complex Z.[1]
9. (c)(v)Z is an octahedral complex with formula [Ni(H₂O)₂(Val)₂]. Use this information to state the type of ligand that the valinate ion is acting as in this complex.[1]

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