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Spin-forbidden Reactions
In chemistry, the selection rule (also known as the transition rule) formally restricts certain reactions, known as spin-forbidden reactions, from occurring due to a required change between two differing quantum states. When a reactant exists in one spin state and the product exists in a different spin state, the corresponding reaction will have an 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. Case of some cobalt carbonyls Singlet and triplet states can occur within organometallic complexes as well, such as Tp''i''-Pr,MeCo(CO)2 and Tp''i''-Pr,MeCo(CO), respectively. Changing spin states When a reaction converts a metal from a singlet to triplet state (or ''vice versa''): # The energy of the two spin states must be nearly equal, as dictated by temperature, # A mechanism is required to change spin stat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chemistry
Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds made of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo during a Chemical reaction, reaction 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 properties ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eigenvalues And Eigenvectors
In linear algebra, an eigenvector () or characteristic vector of a linear transformation is a nonzero vector that changes at most by a scalar factor when that linear transformation is applied to it. The corresponding eigenvalue, often denoted by \lambda, is the factor by which the eigenvector is scaled. Geometrically, an eigenvector, corresponding to a real nonzero eigenvalue, points in a direction in which it is stretched by the transformation and the eigenvalue is the factor by which it is stretched. If the eigenvalue is negative, the direction is reversed. Loosely speaking, in a multidimensional vector space, the eigenvector is not rotated. Formal definition If is a linear transformation from a vector space over a field into itself and is a nonzero vector in , then is an eigenvector of if is a scalar multiple of . This can be written as T(\mathbf) = \lambda \mathbf, where is a scalar in , known as the eigenvalue, characteristic value, or characteristic root ass ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 * E!, a defunct Canadian television system that went by the name CH from 2001 to 2007 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 co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carbon–hydrogen Bond Activation
In organic chemistry, carbon–hydrogen bond functionalization ( functionalization) is a type of organic reaction in which a carbon–hydrogen bond is cleaved and replaced with a bond (where X is usually carbon, oxygen, or nitrogen). The term usually implies that a transition metal is involved in the cleavage process. Reactions classified by the term typically involve the hydrocarbon first to react with a metal catalyst to create an organometallic complex in which the hydrocarbon is coordinated to the inner-sphere of a metal, either via an intermediate "alkane or arene complex" or as a transition state leading to a "" intermediate. The intermediate of this first step (known as activation and sometimes used interchangeably with functionalization) can then undergo subsequent reactions to produce the functionalized product. Important to this definition is the requirement that during the cleavage event, the hydrocarbyl species remains associated in the inner-sphere and under ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Insertion Reaction
An insertion reaction is a chemical reaction where one chemical entity (a molecule or molecular fragment) interposes itself into an existing bond of typically a second chemical entity ''e.g.'': : + \longrightarrow The term only refers to the result of the reaction and does not suggest a mechanism. Insertion reactions are observed in organic, inorganic, and organometallic chemistry. In cases where a metal-ligand bond in a coordination complex is involved, these reactions are typically organometallic in nature and involve a bond between a transition metal and a carbon or hydrogen. It is usually reserved for the case where the coordination number and oxidation state of the metal remain unchanged. When these reactions are reversible, the removal of the small molecule from the metal-ligand bond is called extrusion or elimination. There are two common insertion geometries— 1,1 and 1,2 (pictured above). Additionally, the inserting molecule can act either as a nucleophile or a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Steric Effects
Steric effects arise from the spatial arrangement of atoms. When atoms come close together there is a rise in the energy of the molecule. Steric effects are nonbonding interactions that influence the shape ( conformation) and reactivity of ions and molecules. Steric effects complement electronic effects, which dictate the shape and reactivity of molecules. Steric repulsive forces between overlapping electron clouds result in structured groupings of molecules stabilized by the way that opposites attract and like charges repel. Steric hindrance Steric hindrance is a consequence of steric effects. Steric hindrance is the slowing of chemical reactions due to steric bulk. It is usually manifested in ''intermolecular reactions'', whereas discussion of steric effects often focus on ''intramolecular interactions''. Steric hindrance is often exploited to control selectivity, such as slowing unwanted side-reactions. Steric hindrance between adjacent groups can also affect torsional ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reductive Elimination
Reductive elimination is an elementary step in organometallic chemistry in which the oxidation state of the metal center decreases while forming a new covalent bond between two ligands. It is the microscopic reverse of oxidative addition, and is often the product-forming step in many catalytic processes. Since oxidative addition and reductive elimination are reverse reactions, the same mechanisms apply for both processes, and the product equilibrium depends on the thermodynamics of both directions. General information Reductive elimination is often seen in higher oxidation states, and can involve a two-electron change at a single metal center (mononuclear) or a one-electron change at each of two metal centers (binuclear, dinuclear, or bimetallic). For mononuclear reductive elimination, the oxidation state of the metal decreases by two, while the d-electron count of the metal increases by two. This pathway is common for d8 metals Ni(II), Pd(II), and Au(III) and d6 metals Pt(I ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oxidative Addition
Oxidative addition and reductive elimination are two important and related classes of reactions in organometallic chemistry. Oxidative addition is a process that increases both the oxidation state and coordination number of a metal centre. Oxidative addition is often a step in catalytic cycles, in conjunction with its reverse reaction, reductive elimination. Role in transition metal chemistry For transition metals, oxidative reaction results in the decrease in the d''n'' to a configuration with fewer electrons, often 2e fewer. Oxidative addition is favored for metals that are (i) basic and/or (ii) easily oxidized. Metals with a relatively low oxidation state often satisfy one of these requirements, but even high oxidation state metals undergo oxidative addition, as illustrated by the oxidation of Pt(II) with chlorine: : tCl4sup>2− + Cl2 → tCl6sup>2− In classical organometallic chemistry, the formal oxidation state of the metal and the electron count of the complex both in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coordination Sphere
In coordination chemistry, the first coordination sphere refers to the array of molecules and ions (the ligands) directly attached to the central metal atom. The second coordination sphere consists of molecules and ions that attached in various ways to the first coordination sphere. First coordination sphere The first coordination sphere refers to the molecules that are attached directly to the metal. The interactions between the first and second coordination spheres usually involve hydrogen-bonding. For charged complexes, ion pairing is important. In hexamminecobalt(III) chloride ( o(NH3)6l3), the cobalt cation plus the 6 ammonia ligands comprise the first coordination sphere. The coordination sphere of this ion thus consists of a central MN6 core "decorated" by 18 N−H bonds that radiate outwards. Second coordination sphere Metal ions can be described as consisting of series of two concentric coordination spheres, the first and second. More distant from the second coo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ligand
In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electron pairs, often through Lewis bases. The nature of metal–ligand bonding can range from covalent to ionic. Furthermore, the metal–ligand bond order can range from one to three. Ligands are viewed as Lewis bases, although rare cases are known to involve Lewis acidic "ligands". Metals and metalloids are bound to ligands in almost all circumstances, although gaseous "naked" metal ions can be generated in a high vacuum. Ligands in a complex dictate the reactivity of the central atom, including ligand substitution rates, the reactivity of the ligands themselves, and redox. Ligand selection requires critical consideration in many practical areas, including bioinorganic and medicinal chemistry, homogeneous catalysis, and environmental chemi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Landau–Zener Formula
The Landau–Zener formula is an analytic solution to the equations of motion governing the transition dynamics of a two-state quantum system, with a time-dependent Hamiltonian varying such that the energy separation of the two states is a linear function of time. The formula, giving the probability of a diabatic (not adiabatic) transition between the two energy states, was published separately by Lev Landau, Clarence Zener, Ernst Stueckelberg, and Ettore Majorana, in 1932. If the system starts, in the infinite past, in the lower energy eigenstate, we wish to calculate the probability of finding the system in the upper energy eigenstate in the infinite future (a so-called Landau–Zener transition). For infinitely slow variation of the energy difference (that is, a Landau–Zener velocity of zero), the adiabatic theorem tells us that no such transition will take place, as the system will always be in an instantaneous eigenstate of the Hamiltonian at that moment in time. At non-z ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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