Explain why a molecule of glycine (an amino acid with the molecular formula C₂H₅NO₂) can be classified as belonging to two different functional group classes simultaneously, and state the name of each functional group present.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Glycine is the simplest amino acid and is found in many proteins. Its molecular formula is C₂H₅NO₂.
Model answer (4 marks)
Glycine contains a –NH₂ group, which is an amine functional group.
Glycine also contains a –COOH group, which is a carboxylic acid functional group.
Because both functional groups are present independently in the same molecule, glycine can be classified as both an amine and a carboxylic acid.
The coexistence of these two groups defines glycine as an amino acid, a class of compounds that possess both an amine and a carboxylic acid group.
Glycine also contains a –COOH group, which is a carboxylic acid functional group.
Because both functional groups are present independently in the same molecule, glycine can be classified as both an amine and a carboxylic acid.
The coexistence of these two groups defines glycine as an amino acid, a class of compounds that possess both an amine and a carboxylic acid group.
Examiner tips
- Use the exact terms ‘amine’ and ‘carboxylic acid’. Show that both groups are present in the same molecule. Explain that this dual presence allows classification into two classes. Mention the definition of amino acids to justify the final point.
Common mistakes
- Confusing the amide (–CONH₂) with the amine (–NH₂). Forgetting to state both functional groups explicitly. Using vague wording such as ‘two groups’ without naming them.
Mark scheme (4 marks)
- Glycine contains an amine (–NH₂) functional group
- Glycine contains a carboxylic acid (–COOH) functional group
- Because each functional group is independently present in the same molecule, it can be classified as both an amine and a carboxylic acid
- The presence of two functional groups in one molecule means glycine belongs to the class of compounds called amino acids, which are defined by having both an amine and a carboxylic acid group
Key terms in this question
Related
- All IB DP Chemistry Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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