Protonation
In chemistry, protonation (or hydronation) is the adding of a
conjugate acid.[1] (The complementary process, when a proton is removed from a Brønsted–Lowry acid, is deprotonation
.) Some examples include
- The protonation of water by sulfuric acid:
- H2SO4 + H2O ⇌ H3O+ + HSO−
4
- H2SO4 + H2O ⇌ H3O+ + HSO−
- The protonation of isobutene in the formation of a carbocation:
- (CH3)2C=CH2 + HBF4 ⇌ (CH3)3C+ + BF−
4
- (CH3)2C=CH2 + HBF4 ⇌ (CH3)3C+ + BF−
- The protonation of ammonia in the formation of ammonium chloride from ammonia and hydrogen chloride:
Protonation is a fundamental chemical reaction and is a step in many
oxidation potential, and optical properties
can change.
Rates
Protonations are often rapid, partly because of the high mobility of protons in many solvents. The
strong acids. The rates of protonation and deprotonation can be especially slow when protonation induces significant structural changes.[2]
Reversibility and catalysis
Protonation is usually reversible, and the structure and bonding of the conjugate base are normally unchanged on protonation. In some cases, however, protonation induces isomerization, for example cis-alkenes can be converted to trans-alkenes using a catalytic amount of protonating agent. Many enzymes, such as the serine hydrolases, operate by mechanisms that involve reversible protonation of substrates.
See also
- Acid dissociation constant
- Deprotonation (or dehydronation)
- Molecular autoionization
References
- ISBN 0-669-04529-2.
- .