Which of the following has the highest pK_a v | vedclass

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(B) $pK_a$ value is inversely proportional to the acid strength $(pK_a = -\log K_a)$.Electron-withdrawing groups ($-I$ effect) like $-Br$ increase the

Vedclass · Accepted Answer

$CH_3-CH_2-COOH$

Vedclass · Answer

(B) $pK_a$ value is inversely proportional to the acid strength $(pK_a = -\log K_a)$.Electron-withdrawing groups ($-I$ effect) like $-Br$ increase the acidity of carboxylic acids by stabilizing the carboxylate anion,thereby decreasing the $pK_a$ value.The closer the $-I$ group is to the $-COOH$ group,or the more $-I$ groups there are,the stronger the acid.$1.$ $CH_3-C(Br)_2-COOH$ (Two $-Br$ groups at $\alpha$-position) is the strongest acid (lowest $pK_a$).$2.$ $CH_3-CH(Br)-COOH$ (One $-Br$ group at $\alpha$-position) is the next strongest.$3.$ $Br-CH_2-CH_2-COOH$ (One $-Br$ group at $\beta$-position) is weaker than the $\alpha$-substituted one.$4.$ $CH_3-CH_2-COOH$ has no electron-withdrawing group,only the electron-donating $+I$ effect of the ethyl group,making it the weakest acid and thus giving it the highest $pK_a$ value.

Which of the following has the highest $pK_a$ value?

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