Which of the following has the highest pK_{a} | vedclass

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(B) The $pK_{a}$ value is inversely proportional to the acidity of the compound. $A$ higher $pK_{a}$ value indicates a weaker acid.Among the given opt

Vedclass · Accepted Answer

$3-$Nitrophenol

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(B) The $pK_{a}$ value is inversely proportional to the acidity of the compound. $A$ higher $pK_{a}$ value indicates a weaker acid.Among the given options,the $-NO_2$ group is a strong electron-withdrawing group $(EWG)$ that increases acidity via $-I$ and $-M$ effects.In $2-$nitrophenol,intramolecular hydrogen bonding stabilizes the conjugate base,increasing acidity.In $4-$nitrophenol,the $-NO_2$ group exerts a strong $-M$ effect,significantly increasing acidity.In $2, 4-$dinitrophenol,two $-NO_2$ groups significantly increase acidity.In $3-$nitrophenol,the $-NO_2$ group is at the meta position,where it only exerts an $-I$ effect (no resonance effect). Therefore,it is the least acidic among the choices,resulting in the highest $pK_{a}$ value.

Which of the following has the highest $pK_{a}$ value?

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