Deprotonation

Deprotonation is the removal of a proton (a hydrogen cation, H⁺) from a molecule, forming the conjugate base. The proton removal decreases positive charge in the molecule and increases negative charge. Deprotonation usually occurs from the donation of electrons or acceptance of the proton using a base, which forms its conjugate acid.

The relative ability of a molecule to give up a proton is measured by its pK_a value. A low pK_a value indicates that the compound is acidic and will easily give up its proton to a base. The pK_a of a compound is determined by many things, but the most significant is the stability of the conjugate base. This is primarily determined by the ability (or inability) of the conjugated base to stabilize negative charge. One of the most important ways of assessing a conjugate base's ability to distribute negative charge is using resonance. Electron withdrawing groups (which can stabilize the molecule by increasing charge distribution) or electron donating groups (which destabilize by decreasing charge distribution) present on a molecule also determine its pK_a. The solvent used can also assist in the stabilization of the negative charge on a conjugated base.

Bases used to deprotonate depend on the pK_a of the compound. When the compound is not particularly acidic, and, as such, the molecule does not give up its proton easily, a base stronger than the commonly known hydroxides is required. Hydrides are one of the many types of powerful deprotonating agents. Common hydrides used are sodium hydride and potassium hydride. The hydride forms hydrogen gas with the proton from the other molecule. However, the production of hydrogen also means that deprotonation using agents that release hydrogen is dangerous and should be done in an inert atmosphere (e.g., nitrogen), as the hydrogen can ignite with the oxygen in the air.

See also

• Protonation
• Hydronium
• Acid dissociation constant