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Spin-forbidden Reactions
In chemistry, reactions that involve a change in spin state are known as spin-forbidden reactions. Such reactions show increased activation energy when compared to a similar reaction in which the spin states of the reactant and product are isomorphic. As a result of this increased activation energy, a decreased rate of reaction is observed. A famous example of spin-forbidden reaction is the very slow reaction of with hydrocarbons. Examples The dissociation of nitrous oxide is a well-studied process: : O atoms have a triplet ground state. Methoxy cation has a triplet ground state. In a mass spectrometer, it dissociates into singlet products (formyl cation and H2): : Numerous spin-forbidden reactions are encountered in transition metal chemistry since many metal ions can adopt multiple spin states. For example, ferrous porphyrin complexes containing one axial donor are high spin ferrous. These complexes, which are represented by myoglobin and hemoglobin, bind CO to give singl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Chemistry
Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo during chemical reaction, reactions with other chemical substance, substances. Chemistry also addresses the nature of chemical bonds in chemical compounds. In the scope of its subject, chemistry occupies an intermediate position between physics and biology. It is sometimes called the central science because it provides a foundation for understanding both Basic research, basic and Applied science, applied scientific disciplines at a fundamental level. For example, chemistry explains aspects of plant growth (botany), the formation of igneous rocks (geology), how atmospheric ozone is formed and how environmental pollutants are degraded (ecology), the prop ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Rotational–vibrational Coupling
In physics, rotational–vibrational coupling occurs when the angular frequency, rotation frequency of a physical system, system is close to or identical to a natural frequency of internal vibration. The animation on the right shows ideal motion, with the force exerted by the spring (device), spring and the distance from the rotation around a fixed axis, center of rotation increasing together linearly with no friction. In rotational-vibrational coupling, angular velocity oscillates. By pulling the circling masses closer together, the spring transfers its stored strain energy into the kinetic energy of the circling masses, increasing their angular velocity. The spring cannot bring the circling masses together, since the spring's pull weakens as the circling masses approach. At some point, the increasing angular velocity of the circling masses overcomes the pull of the spring, causing the circling masses to increasingly distance themselves. This increasingly strains the spring, str ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Quantum Chemistry
Quantum chemistry, also called molecular quantum mechanics, is a branch of physical chemistry focused on the application of quantum mechanics to chemical systems, particularly towards the quantum-mechanical calculation of electronic contributions to physical and chemical properties of Molecule, molecules, Material, materials, and solutions at the atomic level. These calculations include systematically applied approximations intended to make calculations computationally feasible while still capturing as much information about important contributions to the computed Wave function, wave functions as well as to observable properties such as structures, spectra, and Thermodynamics, thermodynamic properties. Quantum chemistry is also concerned with the computation of quantum effects on molecular dynamics and chemical kinetics. Chemists rely heavily on spectroscopy through which information regarding the Quantization (physics), quantization of energy on a molecular scale can be obtained ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Chemical Reactions
A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an energy change as new products are generated. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking of chemical bonds between atoms, with no change to the nuclei (no change to the elements present), and can often be described by a chemical equation. Nuclear chemistry is a sub-discipline of chemistry that involves the chemical reactions of unstable and radioactive elements where both electronic and nuclear changes can occur. The substance (or substances) initially involved in a chemical reaction are called reactants or reagents. Chemical reactions are usually characterized by a chemical change, and they yield one or more products, which usually have properties different from the reactants. Reactio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Energy Of Triplet And Quintet States Of Mn-Oxo Species
Energy () is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of heat and light. Energy is a conserved quantity—the law of conservation of energy states that energy can be converted in form, but not created or destroyed. The unit of measurement for energy in the International System of Units (SI) is the joule (J). Forms of energy include the kinetic energy of a moving object, the potential energy stored by an object (for instance due to its position in a field), the elastic energy stored in a solid object, chemical energy associated with chemical reactions, the radiant energy carried by electromagnetic radiation, the internal energy contained within a thermodynamic system, and rest energy associated with an object's rest mass. These are not mutually exclusive. All living organisms constantly take in and release energy. The Earth's climate and ecosystems processes are driven primarily ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Transition Metal Oxo Complex
A transition metal oxo complex is a coordination complex containing an oxo ligand. Formally O2–, an oxo ligand can be bound to one or more metal centers, i.e. it can exist as a terminal or (most commonly) as bridging ligands. Oxo ligands stabilize high oxidation states of a metal.Nugent, W. A., Mayer, J. M. "Metal-Ligand Multiple Bonds." John Wiley & Sons, New York, 1988. They are also found in several metalloproteins, for example in molybdenum cofactors and in many iron-containing enzymes. One of the earliest synthetic compounds to incorporate an oxo ligand is potassium ferrate (K2FeO4), which was likely prepared by Georg E. Stahl in 1702. Reactivity Olation and acid-base reactions A common reaction exhibited by metal-oxo compounds is olation, the condensation process that converts low molecular weight oxides to polymers with M-O-M linkages. Olation often begins with the deprotonation of a metal-hydroxo complex. It is the basis for mineralization and the precipitation o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
High Spin
Spin states when describing transition metal coordination complexes refers to the potential spin configurations of the central metal's d electrons. For several oxidation states, metals can adopt high-spin and low-spin configurations. The ambiguity only applies to first row metals, because second- and third-row metals are invariably low-spin. These configurations can be understood through the two major models used to describe coordination complexes; crystal field theory and ligand field theory (a more advanced version based on molecular orbital theory). High-spin vs. low-spin Octahedral complexes The Δ splitting of the ''d'' orbitals plays an important role in the electron spin state of a coordination complex. Three factors affect Δ: the period (row in periodic table) of the metal ion, the charge of the metal ion, and the field strength of the complex's ligands as described by the spectrochemical series. Only octahedral complexes of first row transition metals adopt hig ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Manganese Oxo Reactivity
Manganese is a chemical element; it has symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition metal with a multifaceted array of industrial alloy uses, particularly in stainless steels. It improves strength, workability, and resistance to wear. Manganese oxide is used as an oxidising agent, as a rubber additive, and in glass making, fertilisers, and ceramics. Manganese sulfate can be used as a fungicide. Manganese is also an essential human dietary element, important in macronutrient metabolism, bone formation, and free radical defense systems. It is a critical component in dozens of proteins and enzymes. It is found mostly in the bones, but also the liver, kidneys, and brain. In the human brain, the manganese is bound to manganese metalloproteins, most notably glutamine synthetase in astrocytes. Manganese is commonly found in laboratories in the form ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
CH Activation Singlet-Triplet
CH, Ch, cH, or ch may refer to: Arts and entertainment * Television channel (sometimes abbreviated as "ch." for television and cable stations) * ''Chaos;Head'', a video game * '' Clone Hero'', a clone game version of popular rhythm game series ''Guitar Hero''. * CollegeHumor, a comedy website * CH (television system), a defunct Canadian television system later known as E! Businesses * Bemidji Airlines (IATA code CH) * Carolina Herrera, a fashion designer based in New York * Columbia Helicopters, an aircraft manufacturing and operator company based in Aurora, Oregon, United States In language * Ch (digraph), considered a single letter in several Latin-alphabet languages * Chamorro language: ISO 639 alpha-2 language code (ch) Science and technology Chemistry * The methylidyne radical (a carbyne); CH• (or •CH), CH3• (or ⫶CH) * The methylidyne group ≡CH * The methine group (methanylylidene, methylylidene) =CH− Mathematics and computing * Chomsky hierarchy, in compute ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Reagent
In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a substance ''consumed'' in the course of a chemical reaction. ''Solvents'', though involved in the reaction mechanism, are usually not called reactants. Similarly, ''catalysts'' are not consumed by the reaction, so they are not reactants. In biochemistry, especially in connection with enzyme-catalyzed reactions, the reactants are commonly called substrates. Definitions Organic chemistry In organic chemistry, the term "reagent" denotes a chemical ingredient (a compound or mixture, typically of inorganic or small organic molecules) introduced to cause the desired transformation of an organic substance. Examples include the Collins reagent, Fenton's reagent, and Grignard reagents. Analytical chemistry In analytical chemistry, a reag ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Carbon–hydrogen Bond Activation
In organic chemistry and organometallic chemistry, carbon–hydrogen bond activation ( activation) is a type of organic reaction in which a carbon–hydrogen bond is Bond cleavage, cleaved and replaced with a bond (X ≠ H is typically a main group element, like carbon, oxygen, or nitrogen). Some authors further restrict the term C–H activation to reactions in which a C–H bond, one that is typically considered to be "unreactive", interacts with a transition metal center M, resulting in its cleavage and the generation of an organometallic species with an M–C bond. The organometallic intermediate resulting from this step (sometimes known as the activation step) could then undergo subsequent reactions with other reagents, either ''in situ'' (often allowing the transition metal to be used in a Catalysis, catalytic amount) or in a separate step, to produce the Late-stage functionalization, functionalized product. The alternative term functionalization is used to describe any ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
