Organic Chemistry
7 marks · EasyThis question is about esterification and addition polymers. Read the question carefully and answer all parts.
Draw the structural formula of the ester formed when methanol reacts with propanoic acid.
State the type of reaction that occurs during ester formation.
Draw the displayed formula for the repeat unit of poly(propene).
Explain briefly why addition polymers like poly(propene) are described as non-biodegradable.
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(a) Structural formula: CH3COOCH3 (methyl propanoate) · must show correct arrangement of atoms: CH3CH2COOCH3
(b) Esterification (condensation reaction) · must show “esterification” or “condensation” or reference to water being produced
(c) Repeat unit of poly(propene) displayed as: · must show —CH2—CH(CH3)— with bonds shown extending out each end; brackets and subscript n
(d) Addition polymers are non-biodegradable because their strong carbon-carbon bonds make them very unreactive; they cannot be easily broken down by bacteria or natural processes. · must show reference to strong covalent bonds/inertness, reference to difficulty of breakdown by bacteria or natural processes
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Marking points
A1 (a) · 2 marks · Correct structural formula of methyl propanoate, all bonds shown and atoms in correct positions.
B1 (b) · 1 mark · Correctly states 'esterification' or 'condensation reaction' as the type of reaction.
C1 (c) · 2 marks · Displayed formula of poly(propene) repeat unit with side chain CH3, brackets and n, all bonds shown correctly.
D1 (d) · 1 mark · States that poly(propene)/addition polymers have strong covalent C–C bonds or are very unreactive/inert.
D2 (d) · 1 mark · Explains that they do not break down by bacteria/microorganisms or in nature; reference to being non-biodegradable.
Worked solution
a. The structural formula for the ester made from methanol and propanoic acid is methyl propanoate: CH3CH2COOCH3.
b. The type of reaction is called esterification, or a condensation reaction (because water is produced).
c. The repeat unit of poly(propene) is shown below:
d. Addition polymers like poly(propene) are non-biodegradable because they have strong carbon-carbon bonds in the polymer chain. These are very unreactive, so bacteria and natural processes cannot break them down; they remain unchanged in the environment for many years.