JEE Main 2021 · Chemistry · Carbonyl Compounds, Carboxylic Acids and Amines · medium

A ketone X (C5H10O) forms an orange precipitate with 2,4-DNP but gives neither a yellow precipitate with I2/NaOH nor a silver mirror with Tollens'…

Single correct option

A ketone

\mathrm{X}

(

\mathrm{C_5H_{10}O}

) forms an orange precipitate with 2,4-DNP but gives neither a yellow precipitate with

\mathrm{I_2/NaOH}

nor a silver mirror with Tollens' reagent.

\mathrm{X}

is reduced by

\mathrm{NaBH_4}

\mathrm{Y}

, and

\mathrm{Y}

is heated with conc.

\mathrm{H_2SO_4}

to give the major alkene

\mathrm{Z}

. Ozonolysis of

\mathrm{Z}

followed by

\mathrm{Zn/H_2O}

gives

Show answer and solution

Answer: (B) ethanal and propanal

The DNP test shows a carbonyl group; no iodoform means no

\mathrm{CH_3CO-}

unit; no Tollens' result means it is a ketone. Of the

\mathrm{C_5H_{10}O}

ketones, pentan-2-one and 3-methylbutan-2-one both contain

\mathrm{CH_3CO-}

, so

\mathrm{X}

is pentan-3-one,

\mathrm{CH_3CH_2COCH_2CH_3}

\mathrm{NaBH_4}

gives pentan-3-ol (Y). Acid dehydration follows Saytzeff: the only alkene possible is pent-2-ene,

\mathrm{CH_3CH=CHCH_2CH_3}

(Z). Ozonolysis cleaves the double bond into

\mathrm{CH_3CHO}

(ethanal) and

\mathrm{CH_3CH_2CHO}

(propanal).

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