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Hypothetical Compound
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. Some are thought to exist only briefly as reactive intermediates, 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 (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) 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). Hypothetical compounds are oft ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 is therefore not a compound. A compound can be transformed into a different substance by a chemical reaction, which may involve interactions with other substances. In this process, bonds between atoms may be broken and/or new bonds formed. There are four major types of compounds, distinguished by how the constituent atoms are bonded together. Molecular compounds are held together by covalent bonds; ionic compounds are held together by ionic bonds; intermetallic compounds are held together by metallic bonds; coordination complexes are held together by coordinate covalent bonds. Non-stoichiometric compounds form a disputed marginal case. A chemical formula specifies the number of atoms of each element in a compound molecule, using the s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Structural Analog
A structural analog (analogue in modern traditional English; Commonwealth English), also known as a chemical analog or simply an analog, is a compound having a structure similar to that of another compound, but differing from it in respect to a certain component. It can differ in one or more atoms, functional groups, or substructures, which are replaced with other atoms, groups, or substructures. A structural analog can be imagined to be formed, at least theoretically, from the other compound. Structural analogs are often isoelectronic. Despite a high chemical similarity, structural analogs are not necessarily functional analogs and can have very different physical, chemical, biochemical, or pharmacological properties. In drug discovery, either a large series of structural analogs of an initial lead compound are created and tested as part of a structure–activity relationship study or a database is screened for structural analogs of a lead compound. Chemical analogues of il ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dioxygenyl Hexafluoroplatinate
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 is strong enough to oxidise , 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. Preparation Dioxygenyl hexafluoroplatinate can be synthesized from the elements by the action of a mixture of oxygen and fluorine gas on platinum sponge at 450 °C. It can also be prepared by the reaction of oxygen difluoride () with platinum sponge. At 350 °C, platinum tetrafluoride is produced; above 400 °C, dioxygenyl hexafluo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Xenon Hexafluoroplatinate
Xenon hexafluoroplatinate is the product of the reaction of platinum hexafluoride with xenon, in an experiment that proved the chemical reactivity of the noble gases. This experiment was performed by Neil Bartlett at the University of British Columbia, who formulated the product as "Xe+ tF6sup>−", although subsequent work suggests that Bartlett's product was probably a salt mixture and did not in fact contain this specific salt. Preparation "Xenon hexafluoroplatinate" is prepared from xenon and platinum hexafluoride (PtF6) as gaseous solutions in SF6. The reactants are combined at 77 K and slowly warmed to allow for a controlled reaction. Structure The material described originally as "xenon hexafluoroplatinate" is probably not Xe+ tF6sup>−. The main problem with this formulation is "Xe+", which would be a radical and would dimerize or abstract a fluorine atom to give XeF+. Thus, Bartlett discovered that Xe undergoes chemical reactions, but the nature and puri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Standard Enthalpy 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, with all substances in their standard states. The standard pressure value is recommended by IUPAC, although prior to 1982 the value 1.00 atm (101.325 kPa) was used. There is no standard temperature. Its symbol is . The superscript Plimsoll on this symbol indicates that the process has occurred under standard conditions at the specified temperature (usually 25 °C or 298.15 K). Standard states are as follows: # For a gas: the hypothetical state it would have assuming it obeyed the ideal gas equation at a pressure of 1 bar # For a gaseous or solid solute present in a diluted ideal solution: the hypothetical state of concentration of the solute of exactly one mole per liter (1 M) at a pressure of 1 bar extrapolated fro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 in the same issue of the same journal. The cycle is concerned with the formation of an ionic compound from the reaction of a metal (often a Group I or Group II element) with a halogen or other non-metallic element such as oxygen. Born–Haber cycles are used primarily as a means of calculating lattice energy (or more precisely enthalpyThe difference between energy and enthalpy is very small and the two terms are interchanged freely in this article.), which cannot otherwise be measured directly. The lattice enthalpy is the enthalpy change involved in the formation of an ionic compound from gaseous ions (an exothermic process), or sometimes defined as the energy to break the ionic compound into gaseous ions (an endothermic process). A Born ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 molecules, groups of molecules, and solids. It is essential because, apart from relatively recent results concerning the hydrogen molecular ion (dihydrogen cation, see references therein for more details), the quantum many-body problem cannot be solved analytically, much less in closed form. While computational results normally complement the information obtained by chemical experiments, it can in some cases predict hitherto unobserved chemical phenomena. It is widely used in the design of new drugs and materials. Examples of such properties are structure (i.e., the expected positions of the constituent atoms), absolute and relative (interaction) energies, electronic charge density distributions, dipoles and higher multipole moments, vi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polywater
Polywater was a hypothesized polymerized form of water that was the subject of much scientific controversy during the late 1960s. By 1969 the popular press had taken notice and sparked fears of a "polywater gap" in the US. Increased press attention also brought with it increased scientific attention, and as early as 1970 doubts about its authenticity were being circulated. By 1973 it was found to be illusory, being just water with any number of common compounds contaminating it. Today, polywater is best known as an example of pathological science. Background In 1961, the Soviet physicist Nikolai Fedyakin, working at the Technological Institute of Kostroma, Russia, performed measurements on the properties of water which had been condensed in, or repeatedly forced through, narrow quartz capillary tubes. Some of these experiments resulted in what was seemingly a new form of water with a higher boiling point, lower freezing point, and much higher viscosity than ordinary water – ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ethylene Dione
Ethylene dione or ethylenedione, also called dicarbon dioxide, Carbon peroxide, ethenedione, or ethene-1,2-dione, is a chemical compound with the formula or . It is an oxide of carbon (an oxocarbon), and can be described as the carbon-carbon covalent dimer of carbon monoxide. It can also be thought of as the dehydrated form of glyoxylic acid (), or a ketone of ethenone . Synthesis attempts The existence of ethylenedione was first suggested in 1913.H. Staudinger, E. Anthes, ''Ber. Dtsch. Chem. Ges.'' 1913, 46, 1426. However, for over a century the compound had eluded all attempts to synthesize and observe it, and it came to be considered a purely hypothetical compound, or at best an "exceedingly coy molecule". In 2015, a research group reported the creation of ethylenedione — by using laser light to eject an electron from the corresponding stable singly-charged anion — and its spectroscopic characterization. However, the reported spectrum was later found to match that of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thought Experiment
A thought experiment is a hypothetical situation in which a hypothesis, theory, or principle is laid out for the purpose of thinking through its consequences. History The ancient Greek ''deiknymi'' (), or thought experiment, "was the most ancient pattern of mathematical proof", and existed before Euclidean mathematics, where the emphasis was on the conceptual, rather than on the experimental part of a thought-experiment. Johann Witt-Hansen established that Hans Christian Ørsted was the first to use the German term ' (lit. thought experiment) circa 1812. Ørsted was also the first to use the equivalent term ' in 1820. By 1883 Ernst Mach used the term ' in a different way, to denote exclusively the conduct of a experiment that would be subsequently performed as a by his students. Physical and mental experimentation could then be contrasted: Mach asked his students to provide him with explanations whenever the results from their subsequent, real, physical experiment differed ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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. The conjugate bases of this elusive acid are, however, common anions, bisulfite (or hydrogen sulfite) and sulfite. Sulfurous acid is an intermediate species in the formation of acid rain from sulfur dioxide. Raman spectra of solutions of sulfur dioxide in water show only signals due to the molecule and the bisulfite ion, . The intensities of the signals are consistent with the following equilibrium: 17O NMR spectroscopy provided evidence that solutions of sulfurous acid and protonated sulfites contain a mixture of isomers, which is in equilibrium: Attempts to concentrate the solutions of sulfurous acid simply reverses the equilibrium, producing sulfur dioxde and water vapor. A clathrate with the formul a has been crystallised. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Disulfurous Acid
Disulfurous acid or pyrosulfurous acid is an oxoacid of sulfur with the formula H2S2O5. The salts of disulfurous acid are called disulfites or metabisulfites. Disulfurous acid is, like sulfurous acid (H2SO3), a phantom acid, which does not exist in the free state. In contrast to disulfate (), disulfite has two directly connected sulfur atoms. The oxidation state In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ... of the sulfur atom bonded to three oxygen atoms is +5 while that of the other is +3. References Sulfur oxoacids Metabisulfites Hypothetical chemical compounds {{theoretical-chem-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
