For which carboxylic acid,the pK_a is the low | vedclass

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(A) The $pK_a$ value is inversely proportional to the acid strength $(K_a)$.Stronger acids have lower $pK_a$ values.Acid strength depends on the stabi

Vedclass · Accepted Answer

$HC \equiv C - COOH$

Vedclass · Answer

(A) The $pK_a$ value is inversely proportional to the acid strength $(K_a)$.Stronger acids have lower $pK_a$ values.Acid strength depends on the stability of the conjugate base (carboxylate ion).Electron-withdrawing groups $(EWG)$ increase acidity by stabilizing the negative charge on the carboxylate group.The hybridization of the carbon atom attached to the $-COOH$ group affects acidity: $sp > sp^2 > sp^3$.$1$. $HC \equiv C - COOH$: The carbon attached to $-COOH$ is $sp$ hybridized,which is highly electronegative and exerts a strong $-I$ effect.$2$. $CH_2 = CH - COOH$: The carbon is $sp^2$ hybridized,exerting a moderate $-I$ effect.$3$. $CH_3 - CH_2 - COOH$ and $CH_3 - CH_2 - CH_2 - COOH$: These have alkyl groups which exert a $+I$ effect,decreasing acidity.Therefore,$HC \equiv C - COOH$ is the strongest acid and has the lowest $pK_a$ value.

For which carboxylic acid,the $pK_a$ is the lowest :

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