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Protonation

In chemistry, protonation (or hydronation) is the adding of a proton (or hydron, or hydrogen cation), usually denoted by H+, to an atom, molecule, or ion, forming a conjugate acid. (The complementary process, when a proton is removed from a Brønsted–Lowry acid, is deprotonation.) Some examples includeThe protonation of water by sulfuric acid: H2SO4 + H2O ⇌ H3O+ + HSO−4 The protonation of isobutene in the formation of a carbocation: (CH3)2C=CH2 + HBF4 ⇌ (CH3)3C+ + BF−4 The protonation of ammonia in the formation of ammonium chloride from ammonia and hydrogen chloride: NH3(g) + HCl(g) → NH4Cl(s)

Rates
Protonations are often rapid, partly because of the high mobility of protons in many solvents. The rate of protonation is related to the acidity of the protonating species: protonation by weak acids is slower than protonation of the same base by strong acids. The rates of protonation and deprotonation can be especially slow when protonation induces significant structural changes. Enantioselective protonations are under kinetic control, are of considerable interest in organic synthesis. They are also relevant to various biological processes. ==Reversibility and catalysis==
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==
Source: Wikipedia ↗
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