Drawing and naming esters
2 marks · EasyExplain how to work out the structure of the ester formed from pentanoic acid and ethanol.
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Draw the ethanol and pentanoic acid molecules so that their OH groups are close. Remove H2O and join what is left. The result is ethyl pentanoate, with structural formula CH3(CH2)3COOCH2CH3.
Also accept: Explanation mentioning removal of H2O and joining remaining groups in the right order.
Common mistakes: Naming acid before alcohol; Forgetting removal of water
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Marking points
R1 · 1 mark · Describes arranging/aligning the alcohol and carboxylic acid to show their OH groups close/together for reaction.
R2 · 1 mark · States removal of H2O (hydrogen from alcohol, OH from acid), then joining what's left to form the ester linkage.
Worked solution
To find the ester structure, draw ethanol (CH3CH2OH) and pentanoic acid (CH3(CH2)3COOH) so that their OH groups are next to each other.
Remove water (the hydrogen from the alcohol and the OH from the acid), then join the two remaining parts.
The result is ethyl pentanoate: CH3(CH2)3COOCH2CH3.