Chemistry 9701 · AS & A Level · Nitrogen compounds

Nitrogen compounds — practice question

Naturally occurring $\alpha$-amino acids, $\text{RCH(NH}_2)\text{CO}_2\text{H}$, may be described as amphiprotic substances.
(a)[1]

What is meant by the Br\u00f8nsted-Lowry definition of an acid?

(b(i))[3]

Draw diagrams to illustrate hydrogen bonding between alanine's carboxylic acid and amino groups and water molecules.

(b(ii))[2]

Draw the structure for the zwitterionic form of glycine.

(c)[3]

Alanine can be made by reacting $\text{CH}_3\text{CHClCO}_2\text{H}$ with excess ammonia. Outline a mechanism for this reaction using curly arrows.

(d)[2]

Amino acids can produce different ions at different pH values. Suggest the structures of the ions formed from the $\alpha$-amino acids below at the stated pH value. - lysine at pH $1$ - aspartic acid at pH $14$

(e(i))

How many different dipeptides can be synthesised, if each one contains two of the three amino acids alanine, serine and lysine?

(e(ii))[3]

Write the structural formula for one dipeptide that contains serine and alanine.

(f(i))

Define the term stereoisomerism precisely.

(f(ii))

Which of the structures G, H or J is the same as structure F?

(f(iii))[3]

The other two structures, G, H or J, are two of the three remaining possible optical isomers of threonine. Complete the partial structure below to show the fourth optical isomer.

Worked solution & mark scheme

This 17-mark question has a full step-by-step worked solution and mark scheme. One marking point: a Brønsted-Lowry acid donates a proton

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