Question

Among the following the one that gives positive iodoform test upon reaction with $I_2$ and NaOH is

• A.
• B. $PhCH\left(OH\right)C{H}_3$
• C. $C{H}_{3}C{H}_{2}CH\left(OH\right)C{H}_{2}C{H}_3$
• D. $C_6{H}_{5}C{H}_{2}C{H}_{2}OH$

Answer 1

The correct option is B $PhCH\left(OH\right)C{H}_3$

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.

For haloform reaction, 3 hydrogens on alpha carbon are required. Among the given options only (b) contains this group, hence undergo haloform reaction.