Acidity of Carboxylic Acids

Carboxylic Acids (or organic acids) are, as their name implies, acids! I never even gave them a second thought until I came across a section in the Chemistry textbook I’m reading that provided an analysis of why they were acidic. I found it quite fascinating and I hope you do as well.

If we look at the carboxylic group:

carboxyl_group01.png

  1. The additional doubly-bonded oxygen atom is very electronegative and will attract the electrons that are shared in the OH bond, which further polarizes the bond and thus makes the H easier to “pop off.”
  2. After the H detaches from the carboxyl group, it becomes of carboxylate ion, which is negatively charged. The two oxygens then form resonance structures, which stabilizes the anion and “distributes” the negative charge to a greater volume, effectively decreasing the charge density. With the diminished charge density it it less likely to grab a hydrogen from water.

For those of you that may be wondering, the first reason I cited is due to a phenomenon called electron drift.

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