2019 A Level H2 Chemistry Paper 1 Question 21 - Determine Functional Groups that React with NaOH

Here's 2019 A Level H2 Chemistry Paper 1 Question 21.

2019 p1 q21 question

The functional groups present in thyroxine (and mentioned in the options) are:

- carboxylic acid
- phenol
- iodobenzene

The reactions to consider with NaOH are as follows:

1. Acid-base or neutralisation of acidic functional groups

We should be familiar with the acidity of carboxylic acids, phenols and alcohols.

For students who are interested, check out a previous video comparing acidity of organic compounds:

The reactions of acids, phenols and alcohols with bases are given below:

2019 p1 q21 reaction of acidic functional groups with bases

Acids and phenols are acidic enough to react with NaOH.

2. Nucleophilic Substitution of halogenoalkanes

Since the iodine atoms are attached to benzene, they are resonance stabilised hence will not undergo nucleophilic substitution.

3. Hydrolysis of nitriles, esters and amides

There are no functional groups in thyroxine that can be hydrolysed.

Hence we can conclude only -COOH and -OH(phenol) groups will react with NaOH and the answer to this question is option D.

Topic: Carboxylic Acids and Derivatives, Organic Chemistry, A Level Chemistry, Singapore

Back to list of questions for 2019 A Level H2 Chemistry Paper 1

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