Chemistry 9701 · AS & A Level · Nitrogen compounds

Nitrogen compounds — practice question

Amino acids are molecules containing the functional groups $\text{-NH}_2$ and $\text{-COOH}$. Glycine, $\text{H}_2\text{NCH}_2\text{COOH}$, is the simplest amino acid that is stable.
(a(i))[1]

Glycine has an isoelectric point of $6.2$. Define isoelectric point.

(a(ii))[1]

Draw the structure of glycine at $\text{pH }4$.

(b)

Fig. 6.1 illustrates two syntheses that begin with glycine.

(b(i))[1]

State the necessary conditions for reaction 1.

(b(ii))[1]

Identify the reagent used in reaction 2.

(b(iii))[2]

Draw the structure of the organic product $U$ formed when hippuric acid reacts with an excess of $\text{LiAlH}_4$ in reaction 3.

(b(iv))[2]

One molecule of phenylalanine, $R$, may react with one molecule of glycine to produce two dipeptides, $S$ and $T$. $S$ and $T$ are structural isomers. Draw the structures of these dipeptides. The peptide bond formed should be shown fully displayed.

(c(i))[2]

Explain why amides are weaker bases than amines.

(c(ii))[2]

The $\text{p}K_a$ of chloroethanoic acid is $2.86$ whereas the $\text{p}K_a$ of ethanoic acid is $4.76$. Explain the difference between these two $\text{p}K_a$ values.

(d(i))[4]

Complete Table 6.2 for the proton ($^1\text{H}$) NMR spectrum of $V$ recorded in $\text{CDCl}_3$. Table 6.1 provides some relevant data.

(d(ii))[1]

Complete Table 6.3 by placing a tick ($\checkmark$) to show any protons whose peaks are still seen in the proton ($^1\text{H}$) NMR spectrum of $V$ recorded in $\text{D}_2\text{O}$.

(i)[4]

Complete Table 6.2 for the proton ($^1\text{H}$) NMR spectrum of $V$ recorded in $\text{CDCl}_3$. Table 6.1 provides some relevant data.

(ii)[1]

Complete Table 6.3 by placing a tick ($\checkmark$) to show any protons whose peaks are still seen in the proton ($^1\text{H}$) NMR spectrum of V recorded in $\text{D}_2\text{O}$.

Worked solution & mark scheme

This 22-mark question has a full step-by-step worked solution and mark scheme. One marking point: The pH at which a molecule has no overall charge / is zwitterionic.

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