protic

Protic is a term used in chemistry to describe substances that can donate a proton in acid–base reactions. In Brønsted–Lowry theory, a protic substance contains a labile hydrogen atom attached to a highly electronegative atom, typically oxygen or nitrogen, that can be released as H+. In many contexts, protic refers specifically to solvents that can donate hydrogen ions and participate in hydrogen bonding.

Common protic solvents include water, methanol, and ethanol, as well as formic and acetic acids. Ammonia and many amines with N–H bonds can also act as protic solvents in certain solutions, though their acidity is weaker. Protic solvents are characterized by their ability to donate protons and to form strong hydrogen-bond networks, which influences solvation, acidity, and reaction rates. They contrast with aprotic solvents, which lack O–H or N–H groups and do not donate protons, such as dimethyl sulfoxide, acetonitrile, acetone, and dichloromethane.

In practical chemistry, whether a solvent is protic affects reaction mechanisms, especially in nucleophilic substitutions and acid–base reactions, and influences solvation of ions and reactive intermediates. In NMR spectroscopy, deuterated protic solvents (for example, D2O or CD3OD) can exchange labile protons with deuterium, altering spectral features. The term also extends to acids that readily donate a proton, distinguishing them from nonprotic or non-donating bases.