OxoniumIon

An oxonium ion is a positively charged polyatomic ion where oxygen is bonded to three other atoms. It is essentially a protonated alcohol or ether. The most common example is the hydronium ion, H₃O⁺, which forms when a Brønsted-Lowry acid donates a proton to a water molecule. In this case, the oxygen atom in water accepts a proton, resulting in a net positive charge distributed across the molecule. Other examples include protonated ethers (R-O⁺H-R') and protonated alcohols (R-O⁺H₂).

Oxonium ions are important intermediates in many chemical reactions, particularly in acid-catalyzed reactions. Their reactivity stems from the positive charge on the oxygen atom, which makes it a strong electrophile. This electrophilic nature allows them to readily attack electron-rich species. In aqueous solutions, hydronium ions are the primary species responsible for acidity, as defined by the Brønsted-Lowry theory. The concentration of hydronium ions is a direct measure of the acidity of a solution. The stability of oxonium ions can vary depending on the substituents attached to the oxygen atom. Electron-donating groups generally stabilize the positive charge, while electron-withdrawing groups destabilize it.