A hypothetical chemical compound is a
chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
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, due to
steric effects
Steric effects arise from the spatial arrangement of atoms. When atoms come close together there is generally a rise in the energy of the molecule. Steric effects are nonbonding interactions that influence the shape (conformational isomerism, co ...
(e.g.
tetra-''tert''-butylmethane, , chlorine heptafluoride, , or bromine heptafluoride, ) or bond stress (e.g.
tetrahedrane
Tetrahedrane is a hypothetical platonic hydrocarbon with chemical formula and a tetrahedral structure. The molecule would be subject to considerable angle strain and has not been synthesized . However, a number of derivatives have been prepa ...
). Others might turn out to be highly
unstable
In dynamical systems instability means that some of the outputs or internal state (controls), states increase with time, without bounds. Not all systems that are not Stability theory, stable are unstable; systems can also be marginal stability ...
,
decomposing,
isomerizing
In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the existence or possibili ...
,
polymerizing,
rearranging, or
disproportionating. 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. 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 organi ...
(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 ,
astatine heptafluoride ,
polonium(II) fluoride ).
Some "parent compounds" have not been or cannot be isolated, even though stable
structural analog
A structural analog, also known as a chemical analog or simply an analog, is a chemical compound, compound having a chemical structure, structure similar to that of another compound, but differing from it in respect to a certain component.
It can ...
s with
substituent
In organic chemistry, a substituent is one or a group of atoms that replaces (one or more) atoms, thereby becoming a moiety in the resultant (new) molecule.
The suffix ''-yl'' is used when naming organic compounds that contain a single bond r ...
s have been discovered or synthesized (e.g.
borole ). 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
Disulfurous acid, metabisulfurous acid or pyrosulfurous acid is an oxoacid of sulfur with the formula . Its structure is . The salts of disulfurous acid are called disulfites or metabisulfites. Disulfurous acid is, like sulfurous acid (), a phan ...
and
sulfurous acid
Sulfuric(IV) acid (United Kingdom spelling: sulphuric(IV) acid), also known as sulfurous (UK: sulphurous) acid and thionic acid, is the chemical compound with the chemical formula, formula .
Raman spectroscopy, Raman spectra of solutions o ...
, whose salts are stable.
Hypothetical compounds are used in some
thought experiment
A thought experiment is an imaginary scenario that is meant to elucidate or test an argument or theory. It is often an experiment that would be hard, impossible, or unethical to actually perform. It can also be an abstract hypothetical that is ...
s.
Some compounds long regarded as hypothetical have later been isolated.
Ethylene dione was suggested in 1913 and observed spectroscopically in 2015. Another stable compound, potassium trichromate, has been produced in a small scale and is known to be a very powerful
oxidizing agent
An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ''electron donor''). In ot ...
. Sodium trichromate and sodium and potassium tetrachromate have been hypothesized but are yet to be synthesized.
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
Polywater was a hypothesized polymerized form of water that was the subject of much scientific controversy during the late 1960s, first described by Soviet scientist Nikolai Fedyakin. By 1969 the popular press had taken notice of Western attempt ...
,
oxygen tetrafluoride ,
chromium hexafluoride and
osmium octafluoride .
Other examples of hypothetical compounds are
xenon octafluoride ,
pentazole
Pentazole is an aromatic molecule consisting of a five-membered ring with all nitrogen atoms, one of which is bonded to a hydrogen atom. It has the molecular formula . Although strictly speaking a homocyclic, inorganic compound, pentazole has ...
(all nitrogen analog of
azole
Azoles are a class of five-membered heterocyclic compounds containing a nitrogen atom and at least one other non-carbon atom (i.e. nitrogen, sulfur, or oxygen) as part of the ring.
Their names originate from the Hantzsch–Widman nomenclature. Th ...
),
hexazine (all nitrogen analog of
benzene
Benzene is an Organic compound, organic chemical compound with the Chemical formula#Molecular formula, molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar hexagonal Ring (chemistry), ring with one hyd ...
),
octaazacubane
Octaazacubane is a hypothetical explosive allotrope of nitrogen with formula N8, whose molecules have eight atoms arranged into a cube. (By comparison, nitrogen usually occurs as the diatomic molecule N2.) It can be regarded as a cubane-type clu ...
(all nitrogen analog of
cubane
Cubane is a synthetic hydrocarbon compound with the Chemical formula, formula . It consists of eight carbon atoms arranged at the corners of a Cube (geometry), cube, with one hydrogen atom attached to each carbon atom. A solid crystalline substanc ...
),
cyclotrioxidane ,
nitrogen pentafluoride ,
tetrafluoroammonium fluoride .
Despite the fact that rhenium heptahydride 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
Computational chemistry is a branch of chemistry that uses computer simulations to assist in solving chemical problems. It uses methods of theoretical chemistry incorporated into computer programs to calculate the structures and properties of mol ...
.
"
sing
Singing is the art of creating music with the voice. It is the oldest form of musical expression, and the human voice can be considered the first musical instrument. The definition of singing varies across sources. Some sources define singi ...
the
Born–Haber cycle to estimate ... the
heat of formation
In chemistry and thermodynamics, the standard enthalpy of formation or standard heat of formation of a compound is the change of enthalpy during the formation of 1 mole of the substance from its constituent elements in their reference state, wi ...
... 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
based on the stability of
.
References
External links
*{{Commonscatinline, Hypothetical chemical compounds
Hypothetical chemical compounds
Theoretical chemistry