Propanal reacts with CH3MgBr followed by hydrolysis to give A. A is oxidised with PCC to give B. B reacts with CH3MgBr followed by hydrolysis to give C. A is also heated with conc. H2SO4 to give D (mainly but-2-ene). Which compounds give a yellow precipitate with I2/NaOH?

JEE Advanced levelOne or more correct optionsDifficulty 3 of 3si220

Propanal reacts with $CH X_{3} MgBr$ followed by hydrolysis to give A. A is oxidised with PCC to give B. B reacts with $CH X_{3} MgBr$ followed by hydrolysis to give C. A is also heated with conc. $H X_{2} SO X_{4}$ to give D (mainly but-2-ene). Which compounds give a yellow precipitate with $I X_{2} / NaOH$ ?

A is butan-2-ol,

CH X_{3} CH (OH) CH X_{2} CH X_{3}

, B is butan-2-one, C is 2-methylbutan-2-ol and D is but-2-ene. Butan-2-ol is oxidised by hypoiodite to butan-2-one, and butan-2-one has the

CH X_{3} CO X^{-}

group, so both give iodoform. The tertiary alcohol C has no

CH X_{3} CH (OH) X^{-}

unit and the alkene D has no relevant group.