|
Eclipsed Configuration
In chemistry an eclipsed conformation is a conformation in which two substituents X and Y on adjacent atoms A, B are in closest proximity, implying that the torsion angle X–A–B–Y is 0°. Such a conformation can exist in any open chain, single chemical bond connecting two sp3- hybridised atoms, and it is normally a conformational energy maximum. This maximum is often explained by steric hindrance, but its origins sometimes actually lie in hyperconjugation (as when the eclipsing interaction is of two hydrogen atoms). In the example of ethane, two methyl groups are connected with a carbon-carbon sigma bond, just as one might connect two Lego pieces through a single "stud" and "tube". With this image in mind, if the methyl groups are rotated around the bond, they will remain connected; however, the shape will change. This leads to multiple possible three-dimensional arrangements, known as conformations, conformational isomers (conformers), or sometimes rotational isomers ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eclipsed Conformation
In chemistry an eclipsed conformation is a conformation in which two substituents X and Y on adjacent atoms A, B are in closest proximity, implying that the torsion angle X–A–B–Y is 0°. Such a conformation can exist in any open chain, single chemical bond connecting two sp3- hybridised atoms, and it is normally a conformational energy maximum. This maximum is often explained by steric hindrance, but its origins sometimes actually lie in hyperconjugation (as when the eclipsing interaction is of two hydrogen atoms). In the example of ethane, two methyl groups are connected with a carbon-carbon sigma bond, just as one might connect two Lego pieces through a single "stud" and "tube". With this image in mind, if the methyl groups are rotated around the bond, they will remain connected; however, the shape will change. This leads to multiple possible three-dimensional arrangements, known as conformations, conformational isomers (conformers), or sometimes rotational isome ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ethane
Ethane ( , ) is a naturally occurring Organic compound, organic chemical compound with chemical formula . At standard temperature and pressure, ethane is a colorless, odorless gas. Like many hydrocarbons, ethane is List of purification methods in chemistry, isolated on an industrial scale from natural gas and as a petrochemical by-product of oil refinery, petroleum refining. Its chief use is as feedstock for ethylene production. The ethyl group is formally, although rarely practically, derived from ethane. History Ethane was first synthesised in 1834 by Michael Faraday, applying electrolysis of a potassium acetate solution. He mistook the hydrocarbon product of this reaction for methane and did not investigate it further. The process is now called Kolbe electrolysis: : acetate, CH3COO− → CH3• + carbon dioxide, CO2 + electron, e− : CH3• + •CH3 → C2H6 During the period 1847–1849, in an effort to vindicate the radical theory of organic chemistry, Hermann Kolbe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Molecular Mechanics
Molecular mechanics uses classical mechanics to model molecular systems. The Born–Oppenheimer approximation is assumed valid and the potential energy of all systems is calculated as a function of the nuclear coordinates using Force field (chemistry), force fields. Molecular mechanics can be used to study molecule systems ranging in size and complexity from small to large biological systems or material assemblies with many thousands to millions of atoms. All-atomistic molecular mechanics methods have the following properties: * Each atom is simulated as one particle * Each particle is assigned a radius (typically the van der Waals radius), polarizability, and a constant net charge (generally derived from quantum calculations and/or experiment) * Bonded interactions are treated as ''springs'' with an equilibrium distance equal to the experimental or calculated bond length Variants on this theme are possible. For example, many simulations have historically used a ''united-atom'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Microwave Spectroscopy
Microwave spectroscopy is the spectroscopy method that employs microwaves, i.e. electromagnetic radiation at GHz frequencies, for the study of matter. History The ammonia molecule NH3 is shaped like a pyramid 0.38 Å in height, with an equilateral triangle of hydrogens forming the base.The nitrogen situated on the axis has two equivalent equilibrium positions above and below the triangle of hydrogens, and this raises the possibility of the nitrogen tunneling up and down, through the plane of the H-atoms. In 1932 Dennison et al. ... analyzed the vibrational energy of this molecule and concluded that the vibrational energy would be split into pairs by the presence of these two equilibrium positions. The next year Wright and Randall observed ... a splitting of 0.67 cm–1 in far infrared lines, corresponding to a frequency of 20 GHz, the value predicted by theory. In 1934 Cleeton and Williams ... constructed a grating echelle spectrometer in order to measure this splitting directl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nuclear Magnetic Resonance Spectroscopy
Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy or magnetic resonance spectroscopy (MRS), is a Spectroscopy, spectroscopic technique based on re-orientation of Atomic nucleus, atomic nuclei with non-zero nuclear spins in an external magnetic field. This re-orientation occurs with absorption of electromagnetic radiation in the radio frequency region from roughly 4 to 900 MHz, which depends on the Isotope, isotopic nature of the nucleus and increases proportionally to the strength of the external magnetic field. Notably, the resonance frequency of each NMR-active nucleus depends on its chemical environment. As a result, NMR spectra provide information about individual functional groups present in the sample, as well as about connections between nearby nuclei in the same molecule. As the NMR spectra are unique or highly characteristic to individual compounds and functional groups, NMR spectroscopy is one of the most important methods to identify ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electron Diffraction
Electron diffraction is a generic term for phenomena associated with changes in the direction of electron beams due to elastic interactions with atoms. It occurs due to elastic scattering, when there is no change in the energy of the electrons. The negatively charged electrons are scattered due to Coulomb forces when they interact with both the positively charged atomic core and the negatively charged electrons around the atoms. The resulting map of the directions of the electrons far from the sample is called a diffraction pattern, see for instance Figure 1. Beyond patterns showing the directions of electrons, electron diffraction also plays a major role in the contrast of images in electron microscopes. This article provides an overview of electron diffraction and electron diffraction patterns, collective referred to by the generic name electron diffraction. This includes aspects of how in a general way electrons can act as waves, and diffract and interact with matter. It a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quadruple Bond
A quadruple bond is a type of chemical bond between two atoms involving eight electrons. This bond is an extension of the more familiar types of covalent bonds: double bonds and triple bonds. Stable quadruple bonds are most common among the transition metals in the middle of the , such as rhenium, tungsten, technetium, molybdenum and chromium. Typically the ligands that support quadruple bonds are π-donors, not π-acceptors. Quadruple bonds are rare as compared to double bonds and triple bonds, but hundreds of compounds with such bonds have been prepared. History Chromium(II) acetate, Cr2(''μ''-O2CCH3)4(H2O)2, was the first chemical compound containing a quadruple bond to be synthesized. It was described in 1844 by E. Peligot, although its distinctive bonding was not recognized for more than a century. The first crystallographic study of a compound with a quadruple bond was provided by Soviet chemists for salts of . The very short Re–Re distance was noted. This short dist ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Potassium Octachlorodimolybdate
Potassium octachlorodimolybdate (systematically named potassium bis(tetrachloromolybdate)(''Mo''–''Mo'')(4−)) is an inorganic compound with the chemical formula . It is known as a red-coloured, microcrystalline solid. The anion is of historic interest as one of the earliest illustrations of a quadruple bonding. The salt is usually obtained as the pink-coloured dihydrate. The compound is prepared in two steps from molybdenum hexacarbonyl: : : The reaction of the acetate with HCl was first described as providing trimolybdenum compounds, but subsequent crystallographic analysis confirmed that the salt contains the anion, with D4h symmetry, in which the two Mo atoms are linked by a quadruple bond. Each Mo atom is bounded with four ligands by a single bond. Each group is a regular square pyramid, with an Mo atom at the apex, and four Cl atoms at the vertices of the square base of the pyramid A pyramid () is a structure whose visible surfaces are triangular in bro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
X-ray Crystallography
X-ray crystallography is the experimental science of determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to Diffraction, diffract in specific directions. By measuring the angles and intensities of the X-ray diffraction, a crystallography, crystallographer can produce a three-dimensional picture of the density of electrons within the crystal and the positions of the atoms, as well as their chemical bonds, crystallographic disorder, and other information. X-ray crystallography has been fundamental in the development of many scientific fields. In its first decades of use, this method determined the size of atoms, the lengths and types of chemical bonds, and the atomic-scale differences between various materials, especially minerals and alloys. The method has also revealed the structure and function of many biological molecules, including vitamins, drugs, proteins and nucleic acids such as DNA. X-ray crystall ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anti Conformation
In chemistry, rotamers are chemical species that differ from one another primarily due to rotations about one or more single bonds. Various arrangements of atoms in a molecule that differ by rotation about single bonds can also be referred to as conformations. Conformers/rotamers differ little in their energies, so they are almost never separable in a practical sense. Rotations about single bonds are subject to small energy barriers. When the time scale for interconversion is long enough for isolation of individual rotamers (usually arbitrarily defined as a half-life of interconversion of 1000 seconds or longer), the species are termed atropisomers (''see:'' atropisomerism). The Ring flip, ring-flip of substituted cyclohexanes constitutes a common form of conformers. The study of the energetics of bond rotation is referred to as conformational analysis. In some cases, conformational analysis can be used to predict and explain product selectivity, mechanisms, and rates of reaction ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
