NEET 2018 · ChemistryPrevious Year Question

Compound A, $C X_{8} H X_{10} O$ , reacts with $NaOI$ (produced by reacting Y with $NaOH$ ) to yield a yellow precipitate with a characteristic smell. A and Y are respectively

Answer: (A) (A) $C X_{6} H X_{5} CH (OH) CH X_{3}$ (1-phenylethanol) and $I X_{2}$ . \textbf{Answer:} (A) $C X_{6} H X_{5} CH (OH) CH X_{3}$ (1-phenylethanol) and $I X_{2}$ \textbf{Solution:} The yellow precipitate with a characteristic smell is iodoform $CHI X_{3}$ (positive iodoform/haloform test).

A.(A) $C X_{6} H X_{5} CH (OH) CH X_{3}$ (1-phenylethanol) and $I X_{2}$ ✓
B.(B) $C X_{6} H X_{5} CH X_{2} CH X_{2} OH$ (2-phenylethanol) and $I X_{2}$
C.(C) p- $CH X_{3} C X_{6} H X_{4} CH X_{2} OH$ (4-methylbenzyl alcohol) and $I X_{2}$
D.(D) p-Cresol (4-methylphenol) and $I X_{2}$

Correct Answer

(A) (A) $C X_{6} H X_{5} CH (OH) CH X_{3}$ (1-phenylethanol) and $I X_{2}$

Solution & Explanation

\textbf{Answer:} (A) $C X_{6} H X_{5} CH (OH) CH X_{3}$ (1-phenylethanol) and $I X_{2}$ \textbf{Solution:} The yellow precipitate with a characteristic smell is iodoform $CHI X_{3}$ (positive iodoform/haloform test). $NaOI$ is generated from $I X_{2} + NaOH$ , so Y is $I X_{2}$ . The iodoform test is given by alcohols of the type $CH X_{3} CH (OH) X^{-}$ (and methyl ketones). Among the $C X_{8} H X_{10} O$ options, only 1-phenylethanol $C X_{6} H X_{5} CH (OH) CH X_{3}$ has the $CH X_{3} CH (OH) X^{-}$ grouping, so it is oxidised to the methyl ketone $C X_{6} H X_{5} COCH X_{3}$ and then gives $CHI X_{3}$ . $C X_{6} H X_{5} CH (OH) CH X_{3} NaOI CHI X_{3} ↓ + C X_{6} H X_{5} COONa$

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Compound A, CX8​HX10​O, reacts with NaOI (produced by reacting Y with NaOH) to yield a yellow precipitate with a characteristic smell. A and Y are respectively

Solution & Explanation

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Compound A, $C X_{8} H X_{10} O$ , reacts with $NaOI$ (produced by reacting Y with $NaOH$ ) to yield a yellow precipitate with a characteristic smell. A and Y are respectively