Question

Which of the following alcohols is expected to give a haloform test?
(A)1-Pentanol
(B)3-Pentanol
(C)2-Propanol
(D)None of above

Answer 1

Hint: Haloform test is given by carbonyl compounds which have a methyl group attached to the carbonyl carbon atom. This test also gives positive results by alcohols which have a methyl group in their structure.

Complete answer:
-Let us first understand the chemical behavior of haloform reaction. Alcohols containing a methyl group attached to the carbon atom with alcohol functional group also can give this test positive because this alcohol can be oxidized to its corresponding ketone by suitable oxidizing agent.
-In the above question three different alcohols are given in which 1-pentanol is a five carbon compound with alcohol group consisting of the first carbon and a butyl group is attached to it. Coming to 3-pentanol it has two ethyl groups attached on both sides of the C-OH. As these two compounds do not possess methyl groups they cannot give iodoform test.
-In the compound 2-propanol there is one methyl group on both the sides of C-OH. So the compound gives a positive test for haloform. The reaction for the haloform test with 2-propanol is shown below-

Therefore the answer for the above question is option (C)2-propanol.

Note: Haloform test is an identification test for the presence of alcohol, ketone group in a given unknown organic compound. The test is given positive by those ketones with methyl groups attached to the carbonyl carbon atom so it is also used as a distinguishing test for identification of different ketones.