Ethenium has been observed in rarefied gases subjected to radiation.[1] Another preparation method is to react certain proton donors such as [[trihydrogen cation|Шаблон:Chem]], [[helium hydride ion|Шаблон:Chem]], [[diazenylium|Шаблон:Chem]], and Шаблон:Chem with ethane at ambient temperature and pressures below 1 mmHg. (Other donors such as [[methanium|Шаблон:Chem]] and Шаблон:Chem form ethanium preferably to ethenium.)[2]
At room temperature and in a rarefied methane atmosphere, ethanium slowly dissociates to ethenium and Шаблон:Chem. The reaction is much faster at 90 °C.[1]
Stability and reactions
Contrary to some earlier reports, ethenium was found to be largely unreactive towards neutral methane at ambient temperature and low pressure (on the order of 1 mmHg), even though the reaction yielding [[propenium|sec-Шаблон:Chem]] and Шаблон:Chem is believed to be exothermic.[3]
Structure
The structure of ethenium's ground state was in dispute for many years, but it was eventually agreed to be a non-classical structure, with the two carbon atoms and one of the hydrogen atoms forming a three-center two-electron bond. Calculations have shown that higher homologues, like the propyl and n-butyl cations also have bridged structures. Generally speaking, bridging appears to be a common means by which 1° alkyl carbocations achieve additional stabilization. Consequently, true 1° carbocations (with a classical structure) may be rare or nonexistent.Шаблон:Cln
