Question

Draw all constitutional isomers with molecular formula c3h8o, and rank them in terms of increasing acidity:

Answer 1

There are only three constitutional isomers (see the image below).

Ethyl methyl ether is the least acidic because it has only C-H bonds. However, it should be more acidic than an alkane (pKₐ ≈ 50) because of the electron withdrawing effect of the O atom. I would expect it to have pKₐ ≈ 30.

The alcohols are more acidic because the O in the O- H bond is highly electron withdrawing. Alcohols typically have pKₐ ≈ 17.

Alkyl groups are electron-donating. This increases electron density in the OH bond and makes the acid weaker. Propan-2-ol has two methyl groups on the α-carbon, while propan-1-ol has one ethyl group. Thus propan-2-ol should be a slightly weaker acid than propan-1-ol.