Alanine, H₂NCH(CH₃)CO₂H, and glutamic acid, H₂NCH(CH₂CH₂CO₂H)CO₂H, are two naturally occurring amino acids.

1. (a)H₂NCH(CH₃)CO₂H exists as two optical isomers. Draw three-dimensional structures of these two optical isomers.[2]
2. (b)The proton (¹H) NMR spectrum of either alanine in D₂O or glutamic acid in D₂O is shown. [Figure NMR spectrum] State whether this is the spectrum of alanine in D₂O or the spectrum of glutamic acid in D₂O. Explain your answer by reference to the number of peaks and splitting patterns.[3]
3. (c)(i)The mass spectrum of glutamic acid, H₂NCH(CH₂CH₂CO₂H)CO₂H, is obtained. State the m/e value of the molecular ion peak in this spectrum.[1]
4. (c)(ii)The spectrum has peaks with m/e values of 88 and 131. Draw the structures of the ions responsible for these peaks. m/e structure of ion 88 131[2]
5. (d)(i)At pH 11 alanine exists as H₂NCH(CH₃)CO₂⁻ ions and glutamic acid exists as H₂NCH(CH₂CH₂CO₂⁻)CO₂⁻ ions. A mixture of alanine and glutamic acid at pH 11 is subjected to electrophoresis. State how the mixture can be maintained at pH 11 during electrophoresis.[1]
6. (d)(ii)Draw a fully labelled diagram for the apparatus that would be used to carry out this electrophoresis. Your diagram should include the position of the mixture of alanine and glutamic acid at the start of the electrophoresis experiment.[2]
7. (d)(iii)Identify the electrode that each amino acid travels towards during electrophoresis at pH 11.[1]
8. (d)(iv)In a particular electrophoresis experiment at pH 11, the glutamic acid travels 3.4 cm. Alanine travels a shorter distance. Explain the factors that account for the difference in the distances travelled.[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.