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Cation–π Interaction
Cation–π interaction is a noncovalent molecular interaction between the face of an electron-rich π system (e.g. benzene, ethylene, acetylene) and an adjacent cation (e.g. Li+, Na+). This interaction is an example of noncovalent bonding between a monopole (cation) and a quadrupole (π system). Bonding energies are significant, with solution-phase values falling within the same order of magnitude as hydrogen bonds and salt bridges. Similar to these other non-covalent bonds, cation–π interactions play an important role in nature, particularly in protein structure, molecular recognition and enzyme catalysis. The effect has also been observed and put to use in synthetic systems. Origin of the effect Benzene, the model π system, has no permanent dipole moment, as the contributions of the weakly polar carbon–hydrogen bonds cancel due to molecular symmetry. However, the electron-rich π system above and below the benzene ring hosts a partial negative charge. A counterbalan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Electric Quadrupole
A quadrupole or quadrapole is one of a sequence of configurations of things like electric charge or current, or gravitational mass that can exist in ideal form, but it is usually just part of a multipole expansion of a more complex structure reflecting various orders of complexity. Mathematical definition The quadrupole moment tensor ''Q'' is a rank-two tensor—3×3 matrix. There are several definitions, but it is normally stated in the traceless form (i.e. Q_ + Q_ + Q_ = 0). The quadrupole moment tensor has thus nine components, but because of transposition symmetry and zero-trace property, in this form only five of these are independent. For a discrete system of \ell point charges or masses in the case of a gravitational quadrupole, each with charge q_\ell, or mass m_\ell, and position \vec_\ell = \left(r_, r_, r_\right) relative to the coordinate system origin, the components of the ''Q'' matrix are defined by: : Q_ = \sum_\ell q_\ell\left(3r_ r_ - \left\, \vec_\ell \righ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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D-orbital
In atomic theory and quantum mechanics, an atomic orbital is a function describing the location and wave-like behavior of an electron in an atom. This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus. The term ''atomic orbital'' may also refer to the physical region or space where the electron can be calculated to be present, as predicted by the particular mathematical form of the orbital. Each orbital in an atom is characterized by a set of values of the three quantum numbers , , and , which respectively correspond to the electron's energy, angular momentum, and an angular momentum vector component ( magnetic quantum number). Alternative to the magnetic quantum number, the orbitals are often labeled by the associated harmonic polynomials (e.g., ''xy'', ). Each such orbital can be occupied by a maximum of two electrons, each with its own projection of spin m_s. The simple names s orbital, p o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Transition Metals
In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. They are the elements that can use d orbitals as Valence electron#Valence_shell, valence orbitals to form chemical bonds. The lanthanide and actinide elements (the f-block) are called inner transition metals and are sometimes considered to be transition metals as well. Since they are metals, they are lustrous and have good electrical and thermal conductivity. Most (with the exception of Group 11 element, group 11 and Group 12 element, group 12) are hard and strong, and have high melting and boiling temperatures. They form compounds in any of two or more different oxidation states and bind to a variety of ligands to form coordination complexes that are often coloured. They form many useful alloys and are often employed as catalysts in elemental form or in compounds such ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Cyclohexane
Cyclohexane is a cycloalkane with the molecular formula . Cyclohexane is non-polar. Cyclohexane is a colorless, flammable liquid with a distinctive detergent-like odor, reminiscent of cleaning products (in which it is sometimes used). Cyclohexane is mainly used for the industrial production of adipic acid and caprolactam, which are precursors to nylon. Cyclohexyl () is the alkyl substituent of cyclohexane and is abbreviated Cy. Production Modern On an industrial scale, cyclohexane is produced by hydrogenation of benzene in the presence of a Raney nickel catalyst. Producers of cyclohexane account for approximately 11.4% of global demand for benzene. The reaction is highly exothermic, with ΔH(500 K) = -216.37 kJ/mol. Dehydrogenation commenced noticeably above 300 °C, reflecting the favorable entropy for dehydrogenation. : Early Unlike benzene, cyclohexane is not found in natural resources such as coal. For this reason, early investigators synthesized their cyclohex ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Aliphatic
In organic chemistry, hydrocarbons ( compounds composed solely of carbon and hydrogen) are divided into two classes: aromatic compounds and aliphatic compounds (; G. ''aleiphar'', fat, oil). Aliphatic compounds can be saturated, like hexane, or unsaturated, like hexene and hexyne. Open-chain compounds, whether straight or branched, and which contain no rings of any type, are always aliphatic. Cyclic compounds can be aliphatic if they are not aromatic. Structure Aliphatic compounds can be saturated, joined by single bonds (alkanes), or unsaturated, with double bonds (alkenes) or triple bonds ( alkynes). If other elements ( heteroatoms) are bound to the carbon chain, the most common being oxygen, nitrogen, sulfur, and chlorine, it is no longer a hydrocarbon, and therefore no longer an aliphatic compound. The least complex aliphatic compound is methane (CH4). Properties Most aliphatic compounds are flammable, allowing the use of hydrocarbons as fuel, such as met ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Intervalence Charge Transfer
192 px, The intense blue color of Prussian blue is a consequence of an intervalence charge transfer band. In chemistry, intervalence charge transfer, often abbreviated IVCT or even IT, is a type of charge-transfer band that is associated with mixed valence compounds. It is most common for systems with two metal sites differing only in oxidation state. Quite often such electron transfer reverses the oxidation states of the sites. The term is frequently extended to the case of metal-to-metal charge transfer between non-equivalent metal centres. The transition produces a characteristically intense absorption in the electromagnetic spectrum. The band is usually found in the visible or near infrared region of the spectrum and is broad. The process can be described as follows: :LnM+-bridge-M'Ln + hν → LnM-bridge-M'+Ln where L is a bridging ligand In coordination chemistry, a bridging ligand is a ligand that connects two or more atoms, usually metal ions. The ligand may b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Polarizability
Polarizability usually refers to the tendency of matter, when subjected to an electric field, to acquire an electric dipole moment in proportion to that applied field. It is a property of all matter, considering that matter is made up of elementary particles which have an electric charge, namely protons and electrons. When subject to an electric field, the negatively charged electrons and positively charged atomic nuclei are subject to opposite forces and undergo charge separation. Polarizability is responsible for a material's dielectric constant and, at high (optical) frequencies, its refractive index. The polarizability of an atom or molecule is defined as the ratio of its induced dipole moment to the local electric field; in a crystalline solid, one considers the dipole moment per unit cell. Note that the local electric field seen by a molecule is generally different from the macroscopic electric field that would be measured externally. This discrepancy is taken into account by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Dennis A
Dennis or Denis is a first or last name from the Greco-Roman name Dionysius, via one of the Christian saints named Dionysius. The name came from Dionysus, the Greek god of ecstatic states, particularly those produced by wine, which is sometimes said to be derived from the Greek Dios (Διός, "of Zeus") and Nysos or Nysa (Νῦσα), where the young god was raised. Dionysus (or Dionysos; also known as Bacchus in Roman mythology and associated with the Italic Liber), the Thracian god of wine, represents not only the intoxicating power of wine, but also its social and beneficent influences. He is viewed as the promoter of civilization, a lawgiver, and lover of peace—as well as the patron deity of both agriculture and the theater. Dionysus is a god of mystery religious rites, such as those practiced in honor of Demeter and Persephone at Eleusis near Athens. In the Thracian mysteries, he wears the "bassaris" or fox-skin, symbolizing new life. (See also Maenads.) A mediaeval ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Journal Of The American Chemical Society
The ''Journal of the American Chemical Society'' is a weekly peer-reviewed scientific journal that was established in 1879 by the American Chemical Society. The journal has absorbed two other publications in its history, the ''Journal of Analytical and Applied Chemistry'' (July 1893) and the ''American Chemical Journal'' (January 1914). It covers all fields of chemistry. Since 2021, the editor-in-chief is Erick M. Carreira ( ETH Zurich). In 2014, the journal moved to a hybrid open access publishing model. Abstracting and indexing The journal is abstracted and indexed in Chemical Abstracts Service, Scopus, EBSCO databases, ProQuest databases, Index Medicus/ MEDLINE/ PubMed, and the Science Citation Index Expanded. According to the '' Journal Citation Reports'', the journal has a 2021 impact factor of 16.383. Editors-in-chief The following people are or have been editor-in-chief: * 1879–1880 – Hermann Endemann * 1880–1881 – Gideon E. Moore * 1881–1882 – Hermann ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Nitrogenous
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seventh in total abundance in the Milky Way and the Solar System. At standard temperature and pressure, two atoms of the element bond to form N2, a colorless and odorless diatomic gas. N2 forms about 78% of Earth's atmosphere, making it the most abundant uncombined element. Nitrogen occurs in all organisms, primarily in amino acids (and thus proteins), in the nucleic acids ( DNA and RNA) and in the energy transfer molecule adenosine triphosphate. The human body contains about 3% nitrogen by mass, the fourth most abundant element in the body after oxygen, carbon, and hydrogen. The nitrogen cycle describes the movement of the element from the air, into the biosphere and organic compounds, then back into the atmosphere. Many industrially important ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |