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Winstein Reaction
In organic chemistry, the term 2-norbornyl cation (or 2-bicyclo .2.1eptyl cation) describes a carbonium ionic derivative of norbornane. A salt of the 2-norbornyl cation was crystallized and characterized by X-ray crystallography confirmed the non-classical structure. Theory Hypovalency: the non-classical picture Advocates of the non-classical nature of the stable 2-norbornyl cation typically depict the species using either resonance structures or a single structure with partial bonds (''see Figure 2''). This hypovalent interaction can be imagined as the net effect of i) a partial sigma bond between carbons 1 and 6, ii) a partial sigma bond between carbons 2 and 6, and iii) a partial pi bond between carbons 1 and 2. Each partial bond is represented as a full bond in one of the three resonance structures or as a dashed partial bond if the cation is depicted through a single structure. There has been some debate over how much the pi-bonded resonance structure actually contributes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
CSD CIF HIGNAOhires
CSD may refer to: Finance * Central securities depository * Confederate States Dollar * Serbian dinar, by previous ISO 4217 code Organizations Education * California School for the Deaf (other), several institutions * Canyons School District, in Utah, US * Cheltenham School District, in Pennsylvania, US * Christina School District, in Delaware, US * Cleveland School District, in Mississippi, US * Cordova School District, in Alaska, US Other organizations * Canteen Stores Department (India), a chain of stores operated by the Indian Ministry of Defence at military bases * CSD Pakistan (Canteen Stores Department), a chain of stores operated by the Pakistani Ministry of Defence * Chartered Society of Designers, a British learned society for various kinds of design work * Commission on Sustainable Development (1992–2013), a former UN agency * Communication Service for the Deaf, an American non-profit company providing ASL services * Congress of Democratic Trade Unions (Que ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Molecular Orbital Theory
In chemistry, molecular orbital theory (MO theory or MOT) is a method for describing the electronic structure of molecules using quantum mechanics. It was proposed early in the 20th century. The MOT explains the paramagnetic nature of O2, which valence bond theory cannot explain. In molecular orbital theory, electrons in a molecule are not assigned to individual chemical bonds between atoms, but are treated as moving under the influence of the atomic nuclei in the whole molecule. Quantum mechanics describes the spatial and energetic properties of electrons as molecular orbitals that surround two or more atoms in a molecule and contain valence electrons between atoms. Molecular orbital theory revolutionized the study of chemical bonding by approximating the states of bonded electrons – the molecular orbitals – as linear combinations of atomic orbitals (LCAO). These approximations are made by applying the density functional theory (DFT) or Hartree–Fock (HF) models to the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Camphene
Camphene is a bicyclic organic compound. It is one of the most pervasive monoterpenes. As with other terpenes, it is insoluble in water, flammable, colorless, and has a pungent smell. It is a minor constituent of many essential oils such as turpentine, cypress oil, camphor oil, citronella oil, neroli, ginger oil, valerian, and mango. It is produced industrially by isomerization of the more common alpha-pinene using a solid acid catalyst such as titanium dioxide. Camphene is used in the preparation of fragrances and as a food additive for flavoring. These include isobornyl acetate. Biosynthesis Camphene is biosynthesized from linalyl pyrophosphate via a sequence of carbocation Carbocation is a general term for ions with a positively charged carbon atom. In the present-day definition given by the IUPAC, a carbocation is any even-electron cation with significant partial positive charge on a carbon atom. They are further ...ic intermediates. : References {{Authority ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electronic Structure
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 molecules, 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 functions as well as to observable properties such as structures, spectra, and 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 of energy on a molecular scale can be obtained. Common methods are infra-red (IR) spectroscopy, nuclear magnetic re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nonclassical Ion
In chemistry, a nonclassical ion usually refers to carbonium ions, a family of organic cations. They are characterized by delocalized three-center, two-electron bonds. The more stable members are often bi- or polycyclic. Examples Historically, nonclassical ions were invoked to explain unusually fast solvolyses of steroidal, norbornyl, and cyclopropyl halides. Explanations for these rates was once controversial. The 2-norbornyl cation is one of the best characterized carbonium ions: : In fact, it has emerged as the prototype for non-classical ions. As indicated first by low-temperature NMR spectroscopy and confirmed by X-ray crystallography, it has a symmetric structure with an RCH2+ group bonded to an alkene group, stabilized by a bicyclic structure. Solvolyses of cyclopropylcarbinyl, cyclobutyl, and homoallyl esters are also characterized by very large rates, and have been shown to occur via a common nonclassical ion structure in the form of a bicyclobutonium ion. Siehl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Atomic Orbital
In quantum mechanics, an atomic orbital () is a Function (mathematics), function describing the location and Matter wave, wave-like behavior of an electron in an atom. This function describes an electron's Charge density, charge distribution around the Atomic nucleus, atom's nucleus, and can be used to calculate the probability of finding an electron in a specific region around the nucleus. Each orbital in an atom is characterized by a set of values of three quantum numbers , , and , which respectively correspond to electron's energy, its angular momentum, orbital angular momentum, and its orbital angular momentum projected along a chosen axis (magnetic quantum number). The orbitals with a well-defined magnetic quantum number are generally complex-valued. Real-valued orbitals can be formed as linear combinations of and orbitals, and are often labeled using associated Spherical harmonics#Harmonic polynomial representation, harmonic polynomials (e.g., ''xy'', ) which describe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isotope Scrambling
Isotopic labeling (or isotopic labelling) is a technique used to track the passage of an isotope (an atom with a detectable variation in neutron count) through chemical reaction, metabolic pathway, or a Cell (biology), biological cell. The reactant is 'labeled' by replacing one or more specific atoms with their isotopes. The reactant is then allowed to undergo the reaction. The position of the isotopes in the product (chemistry), products is measured to determine what sequence the isotopic atom followed in the reaction or the cell's metabolic pathway. The nuclides used in isotopic labeling may be stable nuclides or radionuclides. In the latter case, the labeling is called radiolabeling. In isotopic labeling, there are multiple ways to detect the presence of labeling isotopes; through their mass, vibrational mode, or radioactive decay. Mass spectrometry detects the difference in an isotope's mass, while infrared spectroscopy detects the difference in the isotope's vibrational modes. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reaction Rate
The reaction rate or rate of reaction is the speed at which a chemical reaction takes place, defined as proportional to the increase in the concentration of a product per unit time and to the decrease in the concentration of a reactant per unit time. Reaction rates can vary dramatically. For example, the oxidative rusting of iron under Earth's atmosphere is a slow reaction that can take many years, but the combustion of cellulose in a fire is a reaction that takes place in fractions of a second. For most reactions, the rate decreases as the reaction proceeds. A reaction's rate can be determined by measuring the changes in concentration over time. Chemical kinetics is the part of physical chemistry that concerns how rates of chemical reactions are measured and predicted, and how reaction-rate data can be used to deduce probable reaction mechanisms. The concepts of chemical kinetics are applied in many disciplines, such as chemical engineering, enzymology and environmental e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transition State
In chemistry, the transition state of a chemical reaction is a particular configuration along the reaction coordinate. It is defined as the state corresponding to the highest potential energy along this reaction coordinate. It is often marked with the double dagger (‡) symbol. As an example, the transition state shown below occurs during the SN2 reaction of bromoethane with a hydroxide anion: The activated complex of a reaction can refer to either the transition state or to other states along the reaction coordinate between reactants and products, especially those close to the transition state. Peter Atkins and Julio de Paula, ''Physical Chemistry'' (8th ed., W.H. Freeman 2006), p.809 According to the transition state theory, once the reactants have passed through the transition state configuration, they always continue to form products. History of concept The concept of a transition state has been important in many theories of the rates at which chemical re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Enantiomer
In chemistry, an enantiomer (Help:IPA/English, /ɪˈnænti.əmər, ɛ-, -oʊ-/ Help:Pronunciation respelling key, ''ih-NAN-tee-ə-mər''), also known as an optical isomer, antipode, or optical antipode, is one of a pair of molecular entities which are mirror images of each other and non-superposable. Enantiomer molecules are like right and left hands: one cannot be superposed onto the other without first being converted to its mirror image. It is solely a relationship of chirality (chemistry), chirality and the permanent three-dimensional relationships among molecules or other chemical structures: no amount of re-orientation of a molecule as a whole or conformational isomerism, conformational change converts one chemical into its enantiomer. Chemical structures with chirality rotate plane-polarized light. A mixture of equal amounts of each enantiomer, a ''racemic mixture'' or a ''racemate'', does not rotate light. Stereoisomers include both enantiomers and diastereomers. Diaste ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
