Question

Iodoform test is not answered by:
(A) ${C_2}{H_5}OH$
(B) $C{H_3}OH$
(C) $C{H_3}COC{H_3}$
(D)

Answer 1

Try to recall that the iodoform test is a qualitative test and is used for the detection of ketones and aldehydes having an alpha methyl group. Now, by using this you can easily answer the given question.

Complete step by step solution:

It is known that iodoform is the organo iodine compound with formula, $CH{I_3}$ . It is a pale yellow, crystalline and volatile compound.

Iodoform test is used for the detection of ketones and aldehydes having an alpha methyl group. Alpha means that it is directly attached to the carbon with the functional group. The reagents used are iodine and sodium hydroxide (NaOH).

When iodine and sodium hydroxide is added to the compound containing ketone or aldehyde with alpha methyl group, a pale yellow precipitate of iodoform ( $CH{I_3}$ ) is formed.

This test can also be used to identify alcohols. If the alcohol is tertiary alcohol then it gives no result as it cannot be oxidised. If the alcohol is primary alcohol then it must be ethanol (as this is oxidised to ethanal). All secondary alcohols give positive results, as they are oxidised to ketones.

Now, coming to the question, we can say that option A, C and D will give iodoform test but option B will not give iodoform test as it is primary alcohol.

Therefore, from above we can conclude that option B is the correct option to the given question.

Note:

It should be remembered that ethanal is the only aldehyde which gives an iodoform test.

Also, you should remember that this test takes place in basic medium as basic medium leads to the formation of carbanion.

The condition for iodoform reaction to reach completion is that the number of side products to be kept is less than the number of alpha hydrogen.