odors. For example, acetic acid (ethanoic acid) is the main ingredient in vinegar; propionic acid
(propanoic acid) gives Swiss cheese its smell; butyric acid (butanoic acid) is found in rancid butter
and body odor.
So what makes carboxylic acids so interesting and versatile? First, they’re acids, so they like to give
away protons—particularly because when they do so, the remaining negative charge resonates
between two oxygen atoms, making the anion very stable. This makes carboxylic acids some of the
most acidic compounds encountered in organic chemistry, with pKa values between 3 and 6.
Compare this with alcohols, which have an average pKa around 17. Carboxylic acids are also
excellent at hydrogen bonding, which results in large intermolecular forces and high boiling points.
Finally, carboxylic acids are ubiquitous in nature and are synthesized by all living organisms.