In
chemistry, ethenium, protonated ethylene or ethyl cation is a
positive ion with the formula C
2H+
5. It can be viewed as a molecule of
ethylene (C
2H
4) with one added proton (H+
), or a molecule of
ethane (C
2H
6) minus one
hydride ion (H−
). It is a
carbocation; more specifically, a nonclassical carbocation.
Ethenium has been observed in rarefied gases subjected to radiation.
[1] Another preparation method is to react certain proton donors such as
H+
3,
HeH+
,
N
2H+
, and N
2OH+
with ethane at ambient temperature and pressures below 1 mmHg. (Other donors such as
CH+
5 and HCO+
form ethanium preferably to ethenium.)
[2]
At room temperature and in a rarefied methane atmosphere,
ethanium slowly dissociates to ethenium and H
2. The reaction is much faster at 90 °
C.
[1]
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
sec-C
3H+
7 and H
2 is believed to be
exothermic.
[3]
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.[ clarification needed]
In
chemistry, ethenium, protonated ethylene or ethyl cation is a
positive ion with the formula C
2H+
5. It can be viewed as a molecule of
ethylene (C
2H
4) with one added proton (H+
), or a molecule of
ethane (C
2H
6) minus one
hydride ion (H−
). It is a
carbocation; more specifically, a nonclassical carbocation.
Ethenium has been observed in rarefied gases subjected to radiation.
[1] Another preparation method is to react certain proton donors such as
H+
3,
HeH+
,
N
2H+
, and N
2OH+
with ethane at ambient temperature and pressures below 1 mmHg. (Other donors such as
CH+
5 and HCO+
form ethanium preferably to ethenium.)
[2]
At room temperature and in a rarefied methane atmosphere,
ethanium slowly dissociates to ethenium and H
2. The reaction is much faster at 90 °
C.
[1]
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
sec-C
3H+
7 and H
2 is believed to be
exothermic.
[3]
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.[ clarification needed]