JEE Main · 2023 · 06 Apr 2023 · Shift 2 · Aldehydes Ketones and Carboxylic Acids

The iodoform test is positive for ethanal, for methyl ketones carrying the $\mathrm{C}{\mathrm{H}}_3\mathrm{CO}-$ unit, and for alcohols carrying the $\mathrm{C}{\mathrm{H}}_3\mathrm{CH}(\mathrm{OH})-$ unit, since the latter are first oxidised to a methyl carbonyl which is then cleaved by hypoiodite. 1-Phenylbutan-2-one, $\mathrm{Ph}-\mathrm{C}{\mathrm{H}}_2-\mathrm{CO}-\mathrm{C}{\mathrm{H}}_2\mathrm{C}{\mathrm{H}}_3$, has no methyl group on the carbonyl, and 2-methylbutan-2-ol is a tertiary alcohol that cannot be oxidised, so neither responds. 3-Methylbutan-2-ol and 1-phenylpropan-2-ol each contain the $\mathrm{C}{\mathrm{H}}_3\mathrm{CH}(\mathrm{OH})-$ grouping, 1-phenylethanol is $\mathrm{Ph}-\mathrm{CH}(\mathrm{OH})-\mathrm{C}{\mathrm{H}}_3$, and 3,3-dimethylbutan-2-one is the methyl ketone $(\mathrm{C}{\mathrm{H}}_3{)}_3\mathrm{C}-\mathrm{CO}-\mathrm{C}{\mathrm{H}}_3$, so these four give a positive test. The number of compounds giving a positive iodoform reaction is 4.