Ch_322a_3.015

Ch_322a_3.015 - The Acidity of Carboxylic Acids Carboxylic...

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The Acidity of Carboxylic Acids Carboxylic acids are more acidic than alcohols. CH 3 CO H CH 3 CH 2 O H K a = 1.78 x 10 -5 K a = 1.0 x 10 -16 O = pK a = 4.75 pK a = 16 ! G o = 6.5 kcal/mol ! G o = 21.7 kcal/mol acetic acid ethanol The ! G o values are calculated from the K a values that describe the equilibrium: HA + H 2 O H 3 O + + A -
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Free Energy Diagrams change in free energy CH 3 COOH + H 2 O CH 3 CH 2 OH + H 2 O In the diagrams, the reactant states are set at the same level for easy comparison. The ! G o values indicate that the ionization of acetic acid is much more energetically favorable than the ionization of ethanol. In both reactions, the ion product states are higher in free energy (both ! G o values are positive) than the reactant states. These features are shown in the Free Energy Diagrams below. CH 3 CO 2 + H 3 O ! G o = 6.5 kcal/mol CH 3 CH 2 O + H 3 O ! G o = 21.7 kcal/mol - - + + The ! G o values set the levels of the product states. The ionic state produced from ethanol is much higher in energy than the ionic state produced from acetic acid. This difference in stability may be explained by both resonance theory and the inductive effect .
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Explanations of the Relative Acidities of Ethanol and Acetic Acid Resonance
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Ch_322a_3.015 - The Acidity of Carboxylic Acids Carboxylic...

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