The reaction $\mathrm{R{-}CO{-}X} + \mathrm{Nu}^{-} \longrightarrow \mathrm{R{-}CO{-}Nu} + \mathrm{X}^{-}$ is fastest when X is

JEE Main · 2005 · 08 May 2005 · Offline · Aldehydes Ketones and Carboxylic Acids

The reaction

R - CO - X + Nu^{-} ⟶ R - CO - Nu + X^{-}

is fastest when X is

(A)Cl✓ Correct
(B) $N H_{2}$
(C) $O C_{2} H_{5}$
(D)OCOR

Answer: (A)

Solution

Nucleophilic acyl substitution is fastest for the most reactive acyl derivative, i.e. the one bearing the best leaving group. The reactivity order is acid chloride

>

anhydride

>

ester

>

amide. With

X = Cl

(acyl chloride),

Cl^{-}

is the best leaving group, so the reaction proceeds fastest.

JEE Main · 2005 · 08 May 2005 · Offline · Single correct option

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