Hypothetical chemical compound

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A hypothetical chemical compound is a chemical compound that has been conceived of, but is not known to have been synthesized, observed, or isolated (identified or shown to exist).[ citation needed ]

Contents

Some hypothetical compounds cannot form at all, due to steric effects (e.g. tetra-tert-butylmethane, C(C(CH3)3)4, chlorine heptafluoride, ClF7, or bromine heptafluoride, BrF7) or bond stress (e.g. tetrahedrane C4H4). Others might turn out to be highly unstable, decomposing, isomerizing, polymerizing, rearranging, or disproportionating. Some are thought to exist only briefly as reactive intermediates or in vacuum. Some have no known pathway for synthesis (e.g. hypercubane).

Some compounds of radioactive elements have never been synthesized due to their radioactive decay and short half-lives (e.g. francium hydroxide FrOH, radon hexafluoride RnF6, astatine heptafluoride AtF7, polonium(II) fluoride PoF2).

Some "parent compounds" have not been or cannot be isolated, even though stable structural analogs with substituents have been discovered or synthesized (e.g. borole C4H4BH). Hypothetical compounds are often predicted or expected from known compounds, such as a families of salts for which the "parent acid" is not a stable molecule, or in which salts form with some cations but not others. Examples of such "phantom acids" are disulfurous acid HO−S(=O)−S(=O)2−OH and sulfurous acid O=S(−OH)2, whose salts are stable.

Hypothetical compounds are used in some thought experiments.

Some compounds long regarded as hypothetical have later been isolated. Ethylene dione was suggested in 1913 and observed spectroscopically in 2015. [1] Another stable compound, potassium trichromate, has been produced in a small scale and is known to be a very powerful oxidizing agent. Sodium trichromate and sodium and potassium tetrachromate have been hypothesized but are yet to be synthesized.[ when? ]

Other compounds were once thought to have already been produced, but are now regarded as hypothetical chemical compounds unlikely to ever be produced, such as polywater, oxygen tetrafluoride OF4, chromium hexafluoride CrF6 and osmium octafluoride OsF8.

Other examples of hypothetical compounds are xenon octafluoride XeF8, pentazole N5H (all nitrogen analog of azole), hexazine N6 (all nitrogen analog of benzene), octaazacubane N8 (all nitrogen analog of cubane), cyclotrioxidane O3, nitrogen pentafluoride NF5, tetrafluoroammonium fluoride [NF4]+F−.

Despite the fact that rhenium heptahydride ReH7 has not been isolated, its salt potassium nonahydridorhenate(VII) is stable.

Prediction

Stability and other properties can be predicted using energy calculations and computational chemistry.

"[Using] the Born–Haber cycle to estimate ... the heat of formation ... can be used to determine whether a hypothetical compound is stable." However, "a negative formation enthalpy does not automatically imply the existence of a hypothetical compound." The method predicts that NaCl is stable but NeCl is not. It predicted XePtF6 based on the stability of O2PtF6. [2]

Related Research Articles

In chemistry, noble gas compounds are chemical compounds that include an element from the noble gases, group 18 of the periodic table. Although the noble gases are generally unreactive elements, many such compounds have been observed, particularly involving the element xenon.

<span class="mw-page-title-main">Xenon hexafluoride</span> Chemical compound

Xenon hexafluoride is a noble gas compound with the formula XeF6. It is one of the three binary fluorides of xenon that have been studied experimentally, the other two being XeF2 and XeF4. All known are exergonic and stable at normal temperatures. XeF6 is the strongest fluorinating agent of the series. It is a colorless solid that readily sublimes into intensely yellow vapors.

<span class="mw-page-title-main">Tetrafluoroborate</span> Anion

Tetrafluoroborate is the anion BF−
4. This tetrahedral species is isoelectronic with tetrafluoroberyllate (BeF2−
4), tetrafluoromethane (CF4), and tetrafluoroammonium (NF+
4) and is valence isoelectronic with many stable and important species including the perchlorate anion, ClO−
4, which is used in similar ways in the laboratory. It arises by the reaction of fluoride salts with the Lewis acid BF3, treatment of tetrafluoroboric acid with base, or by treatment of boric acid with hydrofluoric acid.

<span class="mw-page-title-main">Hexafluorosilicic acid</span> Octahedric silicon compound

Hexafluorosilicic acid is an inorganic compound with the chemical formula H
2SiF
6. Aqueous solutions of hexafluorosilicic acid consist of salts of the cation and hexafluorosilicate anion. These salts and their aqueous solutions are colorless.

<span class="mw-page-title-main">Tantalum(V) fluoride</span> Chemical compound

Tantalum(V) fluoride is the inorganic compound with the formula TaF5. It is one of the principal molecular compounds of tantalum. Characteristic of some other pentafluorides, the compound is volatile but exists as an oligomer in the solid state.

<span class="mw-page-title-main">Technetium hexafluoride</span> Chemical compound

Technetium hexafluoride or technetium(VI) fluoride (TcF6) is a yellow inorganic compound with a low melting point. It was first identified in 1961. In this compound, technetium has an oxidation state of +6, the highest oxidation state found in the technetium halides. In this respect, technetium differs from rhenium, which forms a heptafluoride, ReF7. Technetium hexafluoride occurs as an impurity in uranium hexafluoride, as technetium is a fission product of uranium (spontaneous fission in natural uranium, possible contamination from induced fission inside the reactor in reprocessed uranium). The fact that the boiling point of the hexafluorides of uranium and technetium are very close to each other presents a problem in using fluoride volatility in nuclear reprocessing.

Dioxygenyl hexafluoroplatinate is a compound with formula O2PtF6. It is a hexafluoroplatinate of the unusual dioxygenyl cation, O2+, and is the first known compound containing this cation. It can be produced by the reaction of dioxygen with platinum hexafluoride. The fact that PtF
6 is strong enough to oxidise O
2, whose first ionization potential is 12.2 eV, led Neil Bartlett to correctly surmise that it might be able to oxidise xenon (first ionization potential 12.13 eV). This led to the discovery of xenon hexafluoroplatinate, which proved that the noble gases, previously thought to be inert, are able to form chemical compounds.

<span class="mw-page-title-main">Rhenium heptafluoride</span> Chemical compound

Rhenium heptafluoride is the compound with the formula ReF7. It is a yellow low melting solid and is the only thermally stable metal heptafluoride. It has a distorted pentagonal bipyramidal structure similar to IF7, which was confirmed by neutron diffraction at 1.5 K. The structure is non-rigid, as evidenced by electron diffraction studies.

A hexafluoride is a chemical compound with the general formula QXnF6, QXnF6m−, or QXnF6m+. Many molecules fit this formula. An important hexafluoride is hexafluorosilicic acid (H2SiF6), which is a byproduct of the mining of phosphate rock. In the nuclear industry, uranium hexafluoride (UF6) is an important intermediate in the purification of this element.

<span class="mw-page-title-main">Tetrafluoroammonium</span> Chemical compound

The tetrafluoroammonium cation is a positively charged polyatomic ion with chemical formula NF+
4. It is equivalent to the ammonium ion where the hydrogen atoms surrounding the central nitrogen atom have been replaced by fluorine. Tetrafluoroammonium ion is isoelectronic with tetrafluoromethane CF
4, trifluoramine oxide ONF
3, tetrafluoroborate BF−
4 anion and the tetrafluoroberyllate BeF2−
4 anion.

<span class="mw-page-title-main">Nitrosonium octafluoroxenate(VI)</span> Chemical compound

Nitrosonium octafluoroxenate(VI) is a chemical compound of xenon with nitrogen, oxygen, and fluorine, having formula (NO)
2XeF
8. It is an ionic compound containing well-separated nitrosonium cations (NO+) and octafluoroxenate(VI) anions (XeF2−
8). The molecular geometry of the octafluoroxenate(VI) ion is square antiprismatic, having Xe–F bond lengths of 1.971 Å, 1.946 Å, 1.958 Å, 2.052 Å, and 2.099 Å.

<span class="mw-page-title-main">Rhenium hexafluoride</span> Chemical compound

Rhenium hexafluoride, also rhenium(VI) fluoride, (ReF6) is a compound of rhenium and fluorine and one of the seventeen known binary hexafluorides.

Nitrogen pentafluoride is a theoretical compound of nitrogen and fluorine with the chemical formula NF5. It is hypothesized to exist based on the existence of the pentafluorides of the atoms below nitrogen in the periodic table, such as phosphorus pentafluoride. Theoretical models of the nitrogen pentafluoride molecule are either a trigonal bipyramidal covalently bound molecule with symmetry group D3h, or [NF4]+F−, which would be an ionic solid.

Fluorine forms a great variety of chemical compounds, within which it always adopts an oxidation state of −1. With other atoms, fluorine forms either polar covalent bonds or ionic bonds. Most frequently, covalent bonds involving fluorine atoms are single bonds, although at least two examples of a higher order bond exist. Fluoride may act as a bridging ligand between two metals in some complex molecules. Molecules containing fluorine may also exhibit hydrogen bonding. Fluorine's chemistry includes inorganic compounds formed with hydrogen, metals, nonmetals, and even noble gases; as well as a diverse set of organic compounds. For many elements the highest known oxidation state can be achieved in a fluoride. For some elements this is achieved exclusively in a fluoride, for others exclusively in an oxide; and for still others the highest oxidation states of oxides and fluorides are always equal.

<span class="mw-page-title-main">Radon compounds</span>

Radon compounds are chemical compounds formed by the element radon (Rn). Radon is a noble gas, i.e. a zero-valence element, and is chemically not very reactive. The 3.8-day half-life of radon-222 makes it useful in physical sciences as a natural tracer. Because radon is a gas under normal circumstances, and its decay-chain parents are not, it can readily be extracted from them for research.

Osmium heptafluoride is a possible inorganic chemical compound of osmium metal and fluorine with the chemical formula OsF
7. It was first reported in 1966 by the reaction of fluorine and osmium at 600 °C and 400 atm, but no purported synthesis could be reproduced in 2006, giving only osmium hexafluoride instead.

<span class="mw-page-title-main">Radon hexafluoride</span> Chemical compound

Radon hexafluoride is a binary chemical compound of radon and fluorine with the chemical formula RnF
6. This is still a hypothetical compound that has not been synthesized so far.

Osmium fluoride may refer to:

Caesium heptafluoroxenate is an inorganic compound of caesium, and fluorine, and xenon with the chemical formula CsXeF7.

References

  1. ↑ "An elusive molecule—finally revealed". Phys.Org. 2015-07-13. Retrieved 2018-07-10.
  2. ↑ Gregory S. Rohrer (19 July 2001). Structure and Bonding in Crystalline Materials. Cambridge University Press. pp. 293–294. ISBN   9780521663793.
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