JEE Main 2017 · Chemistry · Alcohols, Phenols, Ethers and Haloalkanes · easy

A compound X (C5H12O) evolves hydrogen with sodium and gives turbidity with Lucas reagent at room temperature after about 5 minutes. Oxidation of X…

Single correct option

A compound

X

(

\mathrm{C_5H_{12}O}

) evolves hydrogen with sodium and gives turbidity with Lucas reagent at room temperature after about 5 minutes. Oxidation of

X

with PCC gives

Y

which forms a 2,4-DNP derivative but does not give the iodoform test.

X

A. pentan-1-ol
B. 3-methylbutan-2-ol
C. pentan-3-ol
D. pentan-2-ol

Show answer and solution

Answer: (C) pentan-3-ol

Reaction with Na shows an

\mathrm{-OH}

group. Turbidity in about 5 minutes with Lucas reagent indicates a secondary alcohol (primary: none at room temperature; tertiary: immediate). PCC gives a ketone

Y

(2,4-DNP positive).

Y

not giving iodoform means it is not a methyl ketone. Pentan-2-ol and 3-methylbutan-2-ol give methyl ketones (iodoform positive); pentan-3-ol gives pentan-3-one,

\mathrm{CH_3CH_2COCH_2CH_3}

, which has no

\mathrm{CH_3CO}

group.

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