Illustrated Glossary of Organic Chemistry

Protic: A hydrogen bond donor. Often said of a solvent.

Methanol (CH3OH) is protic because it can donate a hydrogen for hydrogen bonding. In this illustration the hydrogen bond donor molecule is shown in red, and the hydrogen bond acceptor molecule in blue. Other common protic solvents include water (H2O), ethanol (CH3CH2OH), and acetic acid (CH3COOH).

Acetone is aprotic. Its oxygen atom is a hydrogen bond acceptor, the molecule has no hydrogen with enough δ+ charge to be a hydrogen bond donor.