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Absolute Configuration
Absolute configuration refers to the spatial arrangement of atoms within a chiral molecular entity (or group) and its resultant stereochemical description. Absolute configuration is typically relevant in organic molecules, where carbon is bonded to four different substituents. This type of construction creates two possible enantiomers. Absolute configuration uses a set of rules to describe the relative positions of each bond around the chiral center atom. The most common labeling method uses the descriptors ''R'' or ''S'' is based on the Cahn–Ingold–Prelog priority rules. R and S refer to Rectus and Sinister, which are Latin for right and left, respectively. Chiral molecules can differ in their chemical properties, but are identical in their physical properties, which can make distinguishing enantiomers challenging. Absolute configurations for a chiral molecule (in pure form) are most often obtained by X-ray crystallography, although with some important limitations. All ena ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
R S Configuration
R, or r, is the eighteenth letter of the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''ar'' (pronounced ), plural ''ars'', or in Ireland ''or'' . The letter is the eighth most common letter in English and the fourth-most common consonant (after , , and ). The letter is used to form the ending "-re", which is used in certain words such as ''centre'' in some varieties of English spelling, such as British English. Canadian English also uses the "-re" ending, unlike American English, where the ending is usually replaced by "-er" (''center''). This does not affect pronunciation. Name The name of the letter in Latin was (), following the pattern of other letters representing continuants, such as F, L, M, N and S. This name is preserved in French and many other languages. In Middle English, the name of the letter changed from to , following a pattern exhibited in many ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chemical Reaction
A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. 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. Reactions often consist of a sequence of individual sub-steps, the so-called elementary reactions, and the information on the precise course ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Crystallization
Crystallization is the process by which solid forms, where the atoms or molecules are highly organized into a structure known as a crystal. Some ways by which crystals form are precipitating from a solution, freezing, or more rarely deposition directly from a gas. Attributes of the resulting crystal depend largely on factors such as temperature, air pressure, and in the case of liquid crystals, time of fluid evaporation. Crystallization occurs in two major steps. The first is nucleation, the appearance of a crystalline phase from either a supercooled liquid or a supersaturated solvent. The second step is known as crystal growth, which is the increase in the size of particles and leads to a crystal state. An important feature of this step is that loose particles form layers at the crystal's surface and lodge themselves into open inconsistencies such as pores, cracks, etc. The majority of minerals and organic molecules crystallize easily, and the resulting crystals are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Crystal Structure
In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric patterns that repeat along the principal directions of three-dimensional space in matter. The smallest group of particles in the material that constitutes this repeating pattern is the unit cell of the structure. The unit cell completely reflects the symmetry and structure of the entire crystal, which is built up by repetitive translation of the unit cell along its principal axes. The translation vectors define the nodes of the Bravais lattice. The lengths of the principal axes, or edges, of the unit cell and the angles between them are the lattice constants, also called ''lattice parameters'' or ''cell parameters''. The symmetry properties of the crystal are described by the concept of space groups. All possible symmetric arrangements of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tartrate
A tartrate is a salt or ester of the organic compound tartaric acid, a dicarboxylic acid. The formula of the tartrate dianion is O−OC-CH(OH)-CH(OH)-COO− or C4H4O62−. The main forms of tartrates used commercially are pure crystalline tartaric acid used as an acidulant in non-alcoholic drinks and foods, cream of tartar used in baking, and Rochelle salt, commonly used in electroplating solutions. As food additives As food additives, tartrates are used as antioxidants, acidity regulators, and emulsifiers. Examples include *sodium tartrates ( E335) ** monosodium tartrate ** sodium tartrate **sodium ammonium tartrate the compound through which Louis Pasteur discovered chirality *potassium tartrates ( E336) ** potassium bitartrate (monopotassium tartrate, cream of tartar) ** potassium tartrate * potassium sodium tartrate ( E337) * calcium tartrate ( E354, used as emulsifier) *stearyl tartrate ( E483, used as emulsifier) In wine In wine, tartrates are the harmless crystalli ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Resonant Scattering
Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscillating force is applied at a resonant frequency of a dynamic system, the system will oscillate at a higher amplitude than when the same force is applied at other, non-resonant frequencies. Frequencies at which the response amplitude is a relative maximum are also known as resonant frequencies or resonance frequencies of the system. Small periodic forces that are near a resonant frequency of the system have the ability to produce large amplitude oscillations in the system due to the storage of vibrational energy. Resonance phenomena occur with all types of vibrations or waves: there is mechanical resonance, orbital resonance, acoustic resonance, electromagnetic resonance, nuclear magnetic resonance (NMR), electron spin resonance (ESR) and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anomalous Dispersion
In optics, and by analogy other branches of physics dealing with wave propagation, dispersion is the phenomenon in which the phase velocity of a wave depends on its frequency; sometimes the term chromatic dispersion is used for specificity to optics in particular. A medium having this common property may be termed a dispersive medium (plural ''dispersive media''). Although the term is used in the field of optics to describe light and other electromagnetic waves, dispersion in the same sense can apply to any sort of wave motion such as acoustic dispersion in the case of sound and seismic waves, and in gravity waves (ocean waves). Within optics, dispersion is a property of telecommunication signals along transmission lines (such as microwaves in coaxial cable) or the pulses of light in optical fiber. Physically, dispersion translates in a loss of kinetic energy through absorption. In optics, one important and familiar consequence of dispersion is the change in the angle of refra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Johannes Martin Bijvoet
Johannes Martin Bijvoet (23 January 1892, Amsterdam – 4 March 1980, Winterswijk) was a Dutch chemist and crystallographer at the van 't Hoff Laboratory at Utrecht University. He is famous for devising a method of establishing the absolute configuration of molecules. In 1946, he became member of the Royal Netherlands Academy of Arts and Sciences. The concept of tetrahedrally bound carbon in organic compounds stems back to the work by van 't Hoff and Le Bel in 1874. At this time, it was impossible to assign the absolute configuration of a molecule by means other than referring to the projection formula established by Fischer, who had used glyceraldehyde as the prototype and assigned randomly its absolute configuration. In 1949 Bijvoet outlined his principle, which relies on the anomalous dispersion of X-ray radiation. Instead of the normally observed elastic scattering of X-rays when they hit an atom, which generates a scattered wave of the same energy but with a shift in ph ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Relative Absolute Configuration
Relative may refer to: General use *Kinship and family, the principle binding the most basic social units society. If two people are connected by circumstances of birth, they are said to be ''relatives'' Philosophy *Relativism, the concept that points of view have no absolute truth or validity, having only relative, subjective value according to differences in perception and consideration, or relatively, as in the relative value of an object to a person * Relative value (philosophy) Economics *Relative value (economics) Popular culture Film and television * ''Relatively Speaking'' (1965 play), 1965 British play * ''Relatively Speaking'' (game show), late 1980s television game show * ''Everything's Relative'' (episode)#Yu-Gi-Oh! (Yu-Gi-Oh! Duel Monsters), 2000 Japanese anime ''Yu-Gi-Oh! Duel Monsters'' episode *'' Relative Values'', 2000 film based on the play of the same name. *''It's All Relative'', 2003-4 comedy television series *''Intelligence is Relative'', tag line for ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lactic Acid
Lactic acid is an organic acid. It has a molecular formula . It is white in the solid state and it is miscible with water. When in the dissolved state, it forms a colorless solution. Production includes both artificial synthesis as well as natural sources. Lactic acid is an alpha-hydroxy acid (AHA) due to the presence of a hydroxyl group adjacent to the carboxyl group. It is used as a synthetic intermediate in many organic synthesis industries and in various biochemical industries. The conjugate base of lactic acid is called lactate (or the lactate anion). The name of the derived acyl group is lactoyl. In solution, it can ionize by loss of a proton to produce the lactate ion . Compared to acetic acid, its p''K'' is 1 unit less, meaning lactic acid is ten times more acidic than acetic acid. This higher acidity is the consequence of the intramolecular hydrogen bonding between the α-hydroxyl and the carboxylate group. Lactic acid is chiral, consisting of two enantiomer ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zinc
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic table. In some respects, zinc is chemically similar to magnesium: both elements exhibit only one normal oxidation state (+2), and the Zn2+ and Mg2+ ions are of similar size.The elements are from different metal groups. See periodic table. Zinc is the 24th most abundant element in Earth's crust and has five stable isotopes. The most common zinc ore is sphalerite (zinc blende), a zinc sulfide mineral. The largest workable lodes are in Australia, Asia, and the United States. Zinc is refined by froth flotation of the ore, roasting, and final extraction using electricity ( electrowinning). Zinc is an essential trace element for humans, animals, plants and for microorganisms and is necessary for prenatal and postnatal development. I ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isoserine
Isoserine is a non-proteinogenic α-hydroxy-β-amino acid, and an isomer of serine. Non-proteinogenic amino acids do not form proteins, and are not part of the genetic code of any known organism. Isoserine has only been produced synthetically. The first documented synthesis of isoserine in a laboratory setting was by Miyazawa et al., who published their results in 1976. See also * Abiogenesis * Miller–Urey experiment The Miller–Urey experiment (or Miller experiment) is a famous chemistry experiment that simulated the conditions thought at the time (1952) to be present in the atmosphere of the early, prebiotic Earth, in order to test the hypothesis of the ... References Non-proteinogenic amino acids Alpha hydroxy acids {{Biochemistry-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
