chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds made of atoms, molecules and ions ...

, ethanium or protonated ethane is a highly reactive positive ion with formula . It can be described as a molecule of

ethane Ethane ( , ) is an organic chemical compound with chemical formula . At standard temperature and pressure, ethane is a colorless, odorless gas. Like many hydrocarbons, ethane is isolated on an industrial scale from natural gas and as a petr ...

() with one extra

proton A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...

(

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

nucleus Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucle ...

), that gives it a +1

electric charge Electric charge is the physical property of matter that causes charged matter to experience a force when placed in an electromagnetic field. Electric charge can be ''positive'' or ''negative'' (commonly carried by protons and electrons respe ...

. Ethanium is one of the simplest

carbonium ion In chemistry, a carbonium ion is any cation that has a pentavalent carbon atom. The name carbonium may also be used for the simplest member of the class, properly called methanium (), where the five valences are filled with hydrogen atoms. The ...

s (after

methanium In chemistry, methanium is a complex positive ion with formula []+, namely a molecule with one carbon atom covalent bond, bonded to three hydrogen atoms and one hydrogen molecule, bearing a +1 electric charge. It is a superacid and one of the ...

). It was first detected as a rarefied gas in 1960 by

S. Wexler S is the nineteenth letter of the English alphabet. S may also refer to: History * an Anglo-Saxon charter's number in Peter Sawyer's, catalogue Language and linguistics * Long s (ſ), a form of the lower-case letter s formerly used where "s ...

and N. Jesse. It easily dissociates into

ethenium In chemistry, ethenium, protonated ethylene or ethyl cation is a positive ion with the formula . It can be viewed as a molecule of ethylene () with one added proton (), or a molecule of ethane () minus one hydride ion (). It is a carbocation; mor ...

and

molecular hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

Production

Ethanium was first detected by

infrared spectroscopy Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or function ...

among the ions produced by electrical discharges in rarefied

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Eart ...

or ethane gas. Ethanium can also be produced by irradiating methane containing traces of ethane with an

electron beam Cathode rays or electron beam (e-beam) are streams of electrons observed in discharge tubes. If an evacuated glass tube is equipped with two electrodes and a voltage is applied, glass behind the positive electrode is observed to glow, due to ele ...

at low pressure (about 2

mmHg A millimetre of mercury is a manometric unit of pressure, formerly defined as the extra pressure generated by a column of mercury one millimetre high, and currently defined as exactly pascals. It is denoted mmHg or mm Hg. Although not an SI ...

). The electron beam first creates methanium and

methenium In organic chemistry, methenium (also called methylium, carbenium, methyl cation, or protonated methylene) is a cation with the formula . It can be viewed as a methylene radical (:) with an added proton (), or as a methyl radical (•) with one ...

ions. The former rapidly transfer their proton to ethane: : + → + The latter reaction is also observed when , or ions are injected into ethane at somewhat lower pressure.

Stability and reactions

At about 1 mmHg and 30 °C, ethanium dissociates very slowly to ethenium and , across an

energy barrier In chemistry and physics, activation energy is the minimum amount of energy that must be provided for compounds to result in a chemical reaction. The activation energy (''E''a) of a reaction is measured in joules per mole (J/mol), kilojoules pe ...

of about 10

kcal The calorie is a unit of energy. For historical reasons, two main definitions of "calorie" are in wide use. The large calorie, food calorie, or kilogram calorie was originally defined as the amount of heat needed to raise the temperature of on ...

/ mol; the decomposition is considerably faster at 92 °C. The decomposition has been claimed to be nearly athermal but with 8 kcal/mol of free energy due to increase of entropy.

Structure

Like its "unsaturated" relatives ethenium and ethynium , the ethanium ion was conjectured to have (at least momentarily) a proton bound simultaneously to the two

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...

atoms, and the electrical charge evenly spread between them, as in other

non-classical ion Nonclassical carbocations are stabilized by charge delocalization from contributions of neighbouring or bonds, which can form bridged intermediates or transition states. Nonclassical ions have been extensively studied with the 2-norbornyl sys ...

s. The alternative "classical" structure would have the charge and the extra hydrogen bound to only one of the two atoms, i.e. a

methyl In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula . In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in many ...

ated methanium ion. Earlier calculations had predicted that the energies of the two forms should be 4 to 12 kcal/mol lower than the dissociated state + , and they should be separated by a slightly positive energy barrier. Gas-phase

by Yeh and others (1989) has shown that both forms are stable. The bridged structure has the lowest

energy In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of heat a ...

, 4 to 8 kcal/mol lower than the classical one. Refined calculations by Obata and Hirao (1993) predict that the most stable form has three orthogonal planes of symmetry (C_2''v'') with the two subgroups in the

eclipsed configuration In chemistry an eclipsed conformation is a conformation in which two substituents X and Y on adjacent atoms A, B are in closest proximity, implying that the torsion angle X–A–B–Y is 0°. Such a conformation can exist in any open chain, ...

(unlike ethane, whose ground state has the staggered configuration). Four "bottom" H atoms lie on a plane opposite to the bridging H atom and the other two "top" H atoms. The approximate computed distances are C–C 0.211 nm, C–H 0.124 nm (bridging), 0.107 nm (bottom) and 0.108 nm (top); the C–H–C angle at the bridge is about 116 degrees, the H–C–H angles are 116 degrees (bottom-bottom) and 114 degrees (bottom-top). However, there are other configurations with near-minimum energy, including one where the two subgroups are slightly staggered (with C_''s'' symmetry), another where one of the carbons of a ion is loosely bound to an molecule 0.250 nm away.

References

Koop Lammertsma, George A. Olah, Mario Barzaghi, Massimo Simonetta (1972), "Heats of formation of protonated cyclopropane, methylcyclopropane, and ethane". Journal of the American Chemical Society, volume 94, issue 18, pages 6347–6351 Shuang-Ling Chong and J. L. Franklin (1972), "Heats of formation of protonated cyclopropane, methylcyclopropane, and ethane". Journal of the American Chemical Society, volume 94, issue 18, pages 6347–6351. Shigeki Obata and Kimihiko Hirao (1993), "Structure and Vibrational Analysis of Protonated Ethane ", Bulletin of the Chemical Society of Japan volume 66, issue 11, pages 3271-3282 G. I. Mackay, H. I. Schiff, D. K. Bohme (1981), "A room-temperature study of the kinetics and energetics for the protonation of ethane" Canadian Journal of Chemistry, volume 59, issue 12,pages 1771-1778. Margaret French and Paul Kebarle (1975), "Pyrolysis of and other ion-molecule reactions in methane containing traces of ethane". Canadian Journal of Chemistry, volume 53, pages 2268-2274. L. I. Yeh, J. M. Price, and Y. T. Lee (1989), "Infrared spectroscopy of the pentacoordinated carbonium ion ". Journal of the American Chemical Society, volume 111, pages 5591-5604. {{doi, 10.1021/ja00197a015 Carbocations

Production

Stability and reactions

Structure

See also

References