Deprotonation

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Overview

Deprotonation is a chemistry term that refers to the removal of a proton (hydrogen cation H+) from a molecule, forming the conjugate base. The relative ability for a molecule to give up a proton is measured by a pKa value. A low pKa value indicates that the compound is acidic and will easily give up its proton to a base. The pKa of a compound is determined by many things, but most significantly it is impacted by the stability of the conjugate base, that is maily determined by the ability (or inability) of the conjugated base to stabilize the negative charge. The negative charge is stabilized when it is distributed on a large surface or a long chain. One of the mechanisms that distributs the negative charge on a longer chain or a ring is resonance. Solvent also could assist in the stabilization of the negative charge on a conjugated base.

Bases used to deprotonate depend on the pKa of the compound. Where the proton is not particularly acidic, and as such, the molecule does not give up its proton easily, a base stronger than the commonly known hydroxides are required. Hydrides are one of the many types of powerful deprotonating agents. Common hydrides used are sodium hydride and potassium hydride. These bases are so powerful because the hydride forms hydrogen gas when the proton from the other molecule is removed. However, the production of hydrogen also means that deprotonation using agents that release hydrogen are dangerous and should be done in an inert atmosphere (e.g. nitrogen) as water is a source of protons that is present in the air around us all the time and may react with the hydride instead of the desired molecule or may set on fire.

See also


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