# Identify how alcohols can be acidic?

Feb 27, 2016

It's generally contextual.

Alcohols generally have a pKa near $16$, and they are acidic when they are in the presence of a weaker acid, i.e. if that acid's pKa is significantly higher than $16$ (e.g. $20 \text{+}$ is sufficient).

Any Bronsted acid would donate a proton, in addition to being a Lewis acid that accepts electrons from the proton itself as the proton leaves (if the bond breaks, the electrons have to go somewhere, and the distortion of the electron cloud, i.e. generation of the induced dipole is in the direction of the oxygen).

That would be in response to a Lewis base donating electrons to acquire a proton, thereby also exhibiting Bronsted base behavior.

Furthermore, we know that a weaker acid is a stronger base. So an example would be:

Here, the Bronsted acid and Lewis acid are the alcohol, and the Lewis base and Bronsted base are the ammonia. Their conjugates are the alkoxide conjugate base and the ammonium conjugate acid.