2021 P1 Q20 - Deduce Reactants of DOTP

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Let's take a look at 2021 A Levels H2 Chemistry Paper 1 Question 20.

2021 p1 q20 question

We want to determine the reactants that will produce our subject compound DOTP.

The functional group present in DOTP is ester.

We can work backwards and break the ester bond to deduce the structure of the alcohol and acid that form the compound.

2021 p1 q20 deduce reactants

The 2 alcohols are identical with name 2-ethylhexan-1-ol.

The acid is 1,4-dibenzoic acid.

2021 p1 q20 reactants structure

Benzoic acid is not reactive to condensation reactions due to resonance stability.

Therefore it is preferred to convert benzoic acid to benzoyl chloride, which is much more reactive, before esterification.

If we can choose between 1,4-dibenzoyl chloride and 1,4-dibenzoic acid in the options, we will favour 1,4-dibenzoyl chloride.

Let's compare the options to choose our best answer.

2021 p1 q20 option A

Reactants are acid and acid chloride which will not undergo condensation to form ester.

Hence option A is wrong.

2021 p1 q20 option B

Reactants are aliphatic acid chloride and diphenol while we want aliphatic alcohol and dibenzoic acid instead.

Hence option B is wrong.

2021 p1 q20 option C

Reactants are exactly the same as we have deduced previously: 2-ethylhexan-1-ol and 1,4-dibenzoic acid.

Hence option C is our correct answer.

2021 p1 q20 option D

The alcohol is heptan-3-ol which is the wrong alcohol.

Hence option D is wrong.

Topic: Acid and Derivatives, Organic Chemistry, A Level Chemistry, Singapore

Back to list of questions for 2021 A Level H2 Chemistry Paper 1.

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