Chemistry 9701 · AS & A Level · Organic synthesis

Organic synthesis — practice question

Tyrosine can be prepared from phenol by the route shown.
(a(i))[2]

Name the mechanism taking place in the following steps. step 1; step 2.

(a(ii))[1]

What kind of reaction is taking place in step 3?

(a(iii))[5]

Suggest reagents and conditions for each of the following stages. step 1; step 2; step 3; step 5.

(a(iv))[4]

Draw the structures of the products formed when tyrosine reacts with an excess of each of the following reagents: with $\text{NaOH(aq)}$; with $\text{HCl(aq)}$; with $\text{Br}_2\text{(aq)}$.

(iv)[4]

Draw the structures of the products formed when tyrosine reacts with excess of each of the following reagents: with NaOH(aq); with HCl(aq); with Br$_2$(aq).

(b)

The dipeptide phe-tyr has the structure shown below. A mixture containing this dipeptide (phe-tyr) together with its two amino acid components (phe and tyr) was separated by electrophoresis in a buffer at pH 12. When the experiment ended, the results below were observed. Spots R and S stayed very close to each other. The three spots arise from the three species phe, tyr and phe-tyr.

(b(i))[2]

Which species gives spot P? Explain your answer.

(b(ii))[1]

Suggest why the other two species produce spots R and S that are so close together.

Worked solution & mark scheme

This 19-mark question has a full step-by-step worked solution and mark scheme. One marking point: Step 1: electrophilic substitution

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