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).
Some hypothetical compounds cannot form at all. Others might turn out to be highly
unstable,
decomposing,
isomerizing,
polymerizing,
rearranging, or
disproportionating
In chemistry, disproportionation, sometimes called dismutation, is a redox reaction in which one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation states. More generally, the term can b ...
. Some are thought to exist only briefly as
reactive intermediate
In chemistry, a reactive intermediate or an intermediate is a short-lived, high-energy, highly reactive molecule. When generated in a chemical reaction, it will quickly convert into a more stable molecule. Only in exceptional cases can these comp ...
s, or in vacuum (e.g.
helium hydride ion).
Some cannot hold together due to
steric hindrance (e.g.
tetra-''tert''-butylmethane) or bond stress (e.g.
tetrahedrane).
Some have no known pathway for
synthesis
Synthesis or synthesize may refer to:
Science Chemistry and biochemistry
*Chemical synthesis, the execution of chemical reactions to form a more complex molecule from chemical precursors
** Organic synthesis, the chemical synthesis of organ ...
(e.g.
hypercubane
Hypercubane is a hypothetical polycyclic hydrocarbon with the chemical formula C40H24. It is a molecular analog of the four-dimensional hypercube or tesseract. Hypercubane possesses an unconventional geometry of the carbon framework. It has ''Oh'' ...
).
Some compounds of
radioactive elements have never been synthesized due to their radioactive decay and short half-lives (e.g.
francium hydroxide)
Some "parent compounds" have not been or cannot be isolated, even though stable
structural analogs with
substituent
A substituent is one or a group of atoms that replaces (one or more) atoms, thereby becoming a moiety in the resultant (new) molecule. (In organic chemistry and biochemistry, the terms ''substituent'' and ''functional group'', as well as ''side ...
s have been discovered or synthesized (e.g.
borole
Boroles represent a class of molecules known as metalloles, which are heterocyclic 5-membered rings. As such, they can be viewed as structural analogs of cyclopentadiene, pyrrole or furan, with boron replacing a carbon, nitrogen and oxygen atom re ...
).
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. "Phantom acids" such as
disulfurous acid and
sulfurous acid
Sulfurous acid (also sulfuric(IV) acid, sulphurous acid (UK), sulphuric(IV) acid (UK)) is the chemical compound with the formula . There is no evidence that sulfurous acid exists in solution, but the molecule has been detected in the gas phase. ...
.
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.
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.
Prediction
Stability and other properties can be predicted using energy calculations and
computational chemistry
Computational chemistry is a branch of chemistry that uses computer simulation to assist in solving chemical problems. It uses methods of theoretical chemistry, incorporated into computer programs, to calculate the structures and properties of m ...
.
"
singthe
Born–Haber cycle
The Born–Haber cycle is an approach to analyze reaction energies. It was named after the two German scientists Max Born and Fritz Haber, who developed it in 1919. It was also independently formulated by Kasimir Fajans and published concurrently ...
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.
References
External links
*
Theoretical chemistry
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