Question

Which of the following does not answer the iodoform test?
A. n-butyl alcohol
B. sec-butyl alcohol
C. acetophenone
D. acetaldehyde

Answer 1

Hint: Iodoform tests can be used to determine the presence of carbonyl compounds or alcohols. The reaction of Iodine along with the base with methyl ketones results in the appearance of a very pale yellow precipitate of triiodomethane or iodoform.

Complete Step by step solution:
a) Any compounds containing the $C{{H}_{3}}C=O$ group or the $C{{H}_{3}}CH(OH)$ group give a positive result with the iodoform test. When iodine and Sodium hydroxide is added to a compound containing one of these groups, a pale yellow precipitate of iodoform or triiodomethane is formed.
b) Ethanol is the only primary alcohol to give the triiodomethane (iodoform)reaction. Other primary alcohols don’t show iodoform test
c) Let's see the option (A) n-butyl alcohol which is primary alcohol hence iodoform test is not shown by n-butyl alcohol.
d) Option (B) sec-butyl alcohol is secondary alcohol that contains Methyl Groups in Alpha Position hence sec-butyl alcohol show the iodoform test.
e) The option (C) acetophenone is a ketone and Methyl ketones show iodoform test hence acetophenone shows a positive iodoform test.
f) The option (D) acetaldehyde is an aldehyde and acetaldehyde shows a positive iodoform test.

According to the above-mentioned points option (A), n-butyl alcohol is the correct answer

Note: The reaction of iodine and base with methyl ketones is so reliable that the iodoform test is used to probe the presence of a methyl ketone. This is also the case when testing for specific secondary alcohols containing at least one methyl group in alpha-position.