Lactic acid and alanine are both important chemicals in living systems - VCE - SSCE Chemistry - Question 2 - 2003 - Paper 1
Question 2
Lactic acid and alanine are both important chemicals in living systems.
Their structures are:
Lactic Acid:
H O
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H-O-C—C—OH
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H
Alanine: ... show full transcript
Worked Solution & Example Answer:Lactic acid and alanine are both important chemicals in living systems - VCE - SSCE Chemistry - Question 2 - 2003 - Paper 1
Step 1
a. Give the name of the functional group common to both compounds.
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Answer
The functional group common to both lactic acid and alanine is the carboxyl group (-COOH). This group is responsible for the acidic properties of lactic acid and is present in amino acids like alanine.
Step 2
b. Why is alanine classified as an amino acid but lactic acid is not?
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Answer
Alanine is classified as an amino acid because it contains both an amino group (-NH₂) and a carboxyl group (-COOH). Lactic acid, on the other hand, only contains a carboxyl group and lacks the amino group, which is essential for classifying a compound as an amino acid.
Step 3
c. In the boxes below, draw structures of two different possible organic molecules formed by a condensation reaction between lactic acid and alanine.
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Molecule 1:
An amide formed by the reaction of the carboxyl group of lactic acid and the amino group of alanine.
Structure:
HOHO∣∣∣∣∣∣H−O−C—C—N−H+H−O−C—C—OH∣∣∣R1HR2
Molecule 2:
An ester formed by the condensation of the carboxyl group from alanine and the hydroxyl group from lactic acid.
Structure:
HOHO∣∣∣∣∣∣H−O−C—C—O−C—C—OH∣∣∣R1HR2
Step 4
d. For one of the structures given in part c.,
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Answer
i. In the structure of Molecule 1, the new functional group formed is the amide group (
-C(=O)NH-).
ii. The functional group that you have circled is the amide group.
