E.g.ethanoic acid has pK=4.74,(alcohols have pK~16,so carboxylic acids are about 10 times more acidic than alcohols). The reason why carboxylic acids are much more acidic than alcohols is because the carboxylate anion is much more stable than the alkoxide anion. Both alcohols and carboxylic acids are acidic since their respective O-H bonds can be broken heterolytically, giving a proton and an oxygen anion. R一0-H+H,δ：÷ R-6: +H,0冰6 (K,=10-16 alcohol alkoxide K5 R -C-0-H+H,ǒ：。→ R →R H.O+ (K≡105 acid carboxylate R-0- +HO+ R-OH +H2O 0 R-C HO+ R-COOH H2O stabilization carboxylate The difference lies in the fact that the carboxylate anion has the negative charge spread out over two oxygen atoms, whereas the alcohol has the negative charge localized on a single oxygen atom. Ch20 Carboxylic Acids (landscape) Page 8 Ch20 Carboxylic Acids (landscape) Page 8 E.g. ethanoic acid has pKa = 4.74, (alcohols have pKa ~ 16, so carboxylic acids are about 1011 times more acidic than alcohols). The reason why carboxylic acids are much more acidic than alcohols is because the carboxylate anion is much more stable than the alkoxide anion. Both alcohols and carboxylic acids are acidic since their respective O-H bonds can be broken heterolytically, giving a proton and an oxygen anion. The difference lies in the fact that the carboxylate anion has the negative charge spread out over two oxygen atoms, whereas the alcohol has the negative charge localized on a single oxygen atom