Question

Which of the following compounds will give a positive iodoform test?
A. $C_2{H}_{5}OH$ B. $C{H}_{3}CHO$
C. $C{H}_{3}OH$ D. HCHO

• A. Only compound A
• B. Only compound B
• C. Both A and B
• D. Only compounds C and D

Answer 1

The correct option is C Both A and B

Iodoform test is used to check the presence of carbonyl compounds with the structure $R-CO-C{H}_3$ or alcohols with the structure $R-CH\left(OH\right)-C{H}_3$ in a given unknown substance.

When Iodine and sodium hydroxide are added to a compound that contains either a methyl ketone or a secondary alcohol with a methyl group in the alpha position, a pale yellow precipitate of iodoform or triiodomethane is formed. It can be used to identify aldehydes or ketones. If an aldehyde gives a positive iodoform test, then it must be acetaldehyde since it is the only aldehyde with a $C{H}_{3}C=O$ group.



$\therefore$ Ethanol shows positive iodoform test.

Acetaldehyde also shows + ve iodoform test.

But in $C{H}_{3}OH$ and HCHO, there will be no possibility for the formation of
group to give CH$I_3$. C and D show negative iodoform test.
Hence, the correct option is (c).