Question

Which of the following does not give an iodoform test?
A.\[{\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{OH}}\]
B.\[{\text{C}}{{\text{H}}_3}{\text{OH}}\]
C.\[{\text{C}}{{\text{H}}_3}{\text{CHO}}\]
D.\[{\text{PhCOC}}{{\text{H}}_3}\]

Answer 1

Hint:Iodoform test is used to check the presence of carbonyl compound with the structure of \[{\text{C}}{{\text{H}}_3}{\text{C}} = {\text{O}}\] and the secondary alcohol in any given an organic compound. In this reaction basically iodine reacts with a base and the carbonyl compound to form yellow colour precipitate having an antiseptic smell.

Complete step by step answer:
Iodoform test is used to check the presence of carbonyl compound with the structure of \[{\text{C}}{{\text{H}}_3}{\text{C}} = {\text{O}}\] and the secondary alcohol in any given an organic compound. In this reaction basically iodine reacts with a base and the carbonyl compound to form yellow colour precipitate having an antiseptic smell.
The only aldehyde that gave the positive iodoform test is acetaldehyde because acetaldehyde only contains the required functional group that is \[{\text{C}}{{\text{H}}_3}{\text{C}} = {\text{O}}\] . Other aldehydes have higher hydrocarbon chains and hence do not give positive iodoform test. Secondary alcohol that contains methyl group in Alpha position also gives positive iodoform test.
Primary alcohols are those alcohols in which the hydroxide group is attached to that carbon which is directly attached with only one carbon. Secondary alcohols are those alcohols in which the hydroxide group is attached to that carbon which is directly attached to two other carbons.
In option A and option B both are primary alcohols and hence will give negative iodoform test or does not give iodoform test. Whereas option C is acetaldehyde which will give the positive test and optional C is acetophenone which also contain the required functional group and hence will also give the positive iodoform test

So, the correct option is option A and B.

Note:
Iodoform test is widely used in laboratories for the confirmation of carbonyl groups such as ketone and aldehyde and secondary alcohols. The product formed in the idea form reactions are the carboxylic acid group and iodoform. The antiseptic smell and the pale yellow colour occur due to the formation of iodoform.