The K_{eq.} values in HCN addition to the fol | vedclass

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(D) The addition of $HCN$ to an aldehyde is a nucleophilic addition reaction. The equilibrium constant $K_{eq.}$ depends on the electrophilicity of th

Vedclass · Accepted Answer

$II > I > III$

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(D) The addition of $HCN$ to an aldehyde is a nucleophilic addition reaction. The equilibrium constant $K_{eq.}$ depends on the electrophilicity of the carbonyl carbon.Electron-donating groups (like $-OCH_3$ and $-N(CH_3)_2$) decrease the electrophilicity of the carbonyl carbon by resonance ($+M$ effect),thereby decreasing the $K_{eq.}$ value.Comparing the substituents:- In $(II)$,there is no substituent on the benzene ring.- In $(I)$,the $-OCH_3$ group exerts a $+M$ effect.- In $(III)$,the $-N(CH_3)_2$ group exerts a stronger $+M$ effect than $-OCH_3$.Therefore,the electrophilicity order is $(II) > (I) > (III)$,which is also the order of $K_{eq.}$ values.Thus,the correct order is $II > I > III$.

Test	Inference
$(a)$ $2, 4-DNP$ test	Coloured precipitate
$(b)$ Iodoform test	Yellow precipitate
$(c)$ Azo-dye test	No dye formation

The $K_{eq.}$ values in $HCN$ addition to the following aldehydes are in the order:

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Test Inference

$(a)$ $2, 4-DNP$ test Coloured precipitate

$(b)$ Iodoform test Yellow precipitate

$(c)$ Azo-dye test No dye formation

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