Ultraviolet–visible Spectroscopy Of Stereoisomers
Ultraviolet–visible spectroscopy (UV–vis) can distinguish between enantiomers by showing a distinct Cotton effect for each isomer. UV–vis spectroscopy sees only chromophores, so other molecules must be prepared for analysis by chemical addition of a chromophore such as anthracene. Two methods are reported: the octant rule and the exciton chirality method. The octant rule was introduced in 1961 by William Moffitt, R. B. Woodward, A. Moscowitz, William Klyne and Carl Djerassi.''A Simple Computer-Aided Three-Dimensional Molecular Modeling for the Octant Rule'' Yinan Kang , Fu-An Kang J. Chem. Educ., 2011, 88 (4), p 420 This empirical rule allows the prediction of the sign of the Cotton effect by analysing relative orientation of substituents in three dimensions and in this way the absolute configuration Absolute configuration refers to the spatial arrangement of atoms within a chiral molecular entity (or group) and its resultant stereochemical description. Absolute c ... [...More Info...]       [...Related Items...]     OR:     [Wikipedia]   [Google]   [Baidu]   |
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Ultraviolet–visible Spectroscopy
UV spectroscopy or UV–visible spectrophotometry (UV–Vis or UV/Vis) refers to absorption spectroscopy or reflectance spectroscopy in part of the ultraviolet and the full, adjacent visible regions of the electromagnetic spectrum. Being relatively inexpensive and easily implemented, this methodology is widely used in diverse applied and fundamental applications. The only requirement is that the sample absorb in the UV-Vis region, i.e. be a chromophore. Absorption spectroscopy is complementary to fluorescence spectroscopy. Parameters of interest, besides the wavelength of measurement, are absorbance (A) or transmittance (%T) or reflectance (%R), and its change with time. Optical transitions Most molecules and ions absorb energy in the ultraviolet or visible range, i.e., they are chromophores. The absorbed photon excites an electron in the chromophore to higher energy molecular orbitals, giving rise to an excited state. For organic chromophores, four possible types of transitions ... [...More Info...]       [...Related Items...]     OR:     [Wikipedia]   [Google]   [Baidu]   |
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Enantiomer
In chemistry, an enantiomer ( /ɪˈnænti.əmər, ɛ-, -oʊ-/ ''ih-NAN-tee-ə-mər''; from Ancient Greek ἐνάντιος ''(enántios)'' 'opposite', and μέρος ''(méros)'' 'part') – also called optical isomer, antipode, or optical antipode – is one of two stereoisomers that are non-superposable onto their own mirror image. Enantiomers are much like one's right and left hands, when looking at the same face, they cannot be superposed onto each other. No amount of reorientation will allow the four unique groups on the chiral carbon (see Chirality (chemistry)) to line up exactly. The number of stereoisomers a molecule has can be determined by the number of chiral carbons it has. Stereoisomers include both enantiomers and diastereomers. Diastereomers, like enantiomers, share the same molecular formula and are non-superposable onto each other however, they are not mirror images of each other. A molecule with chirality rotates plane-polarized light. A mixture of equals a ... [...More Info...]       [...Related Items...]     OR:     [Wikipedia]   [Google]   [Baidu]   |
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Cotton Effect
The Cotton effect in physics, is the characteristic change in optical rotatory dispersion and/or circular dichroism in the vicinity of an absorption band of a substance. In a wavelength region where the light is absorbed, the absolute magnitude of the optical rotation at first varies rapidly with wavelength, crosses zero at absorption maxima and then again varies rapidly with wavelength but in the opposite direction. This phenomenon was discovered in 1895 by the French physicist Aimé Cotton Aimé Auguste Cotton (9 October 1869 – 16 April 1951) was a French physicist known for his studies of the interaction of light with chiral molecules. In the absorption bands of these molecules, he discovered large values of optical rotator ... (1869–1951). The Cotton effect is called ''positive'' if the optical rotation first increases as the wavelength decreases (as first observed by Cotton), and ''negative'' if the rotation first decreases. A protein structure such as a bet ... [...More Info...]       [...Related Items...]     OR:     [Wikipedia]   [Google]   [Baidu]   |
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Chromophore
A chromophore is the part of a molecule responsible for its color. The color that is seen by our eyes is the one not absorbed by the reflecting object within a certain wavelength spectrum of visible light. The chromophore is a region in the molecule where the energy difference between two separate molecular orbitals falls within the range of the visible spectrum. Visible light that hits the chromophore can thus be absorbed by exciting an electron from its ground state into an excited state. In biological molecules that serve to capture or detect light energy, the chromophore is the moiety that causes a conformational change in the molecule when hit by light. Conjugated pi-bond system chromophores Just like how two adjacent p-orbitals in a molecule will form a pi-bond, three or more adjacent p-orbitals in a molecule can form a conjugated pi-system. In a conjugated pi-system, electrons are able to capture certain photons as the electrons resonate along a certain distance ... [...More Info...]       [...Related Items...]     OR:     [Wikipedia]   [Google]   [Baidu]   |
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Anthracene
Anthracene is a solid polycyclic aromatic hydrocarbon (PAH) of formula C14H10, consisting of three fused benzene rings. It is a component of coal tar. Anthracene is used in the Economic production, production of the red dye alizarin and other dyes. Anthracene is colorless but exhibits a blue (400–500 nm peak) fluorescence under ultraviolet radiation. Occurrence and production Coal tar, which contains around 1.5% anthracene, remains a major source of this material. Common impurities are phenanthrene and carbazole. The mineral form of anthracene is called freitalite and is related to a coal deposit. A classic laboratory method for the preparation of anthracene is by cyclodehydration of o-methyl- or o-methylene-substituted diarylketones in the so-called Elbs reaction, for example from ''o''-tolyl phenyl ketone. Reactions Reduction Reduction of anthracene with alkali metals yields the deeply colored radical anion salts M+[anthracene]− (M = Li, Na, K). Hydrogenation gives 9 ... [...More Info...]       [...Related Items...]     OR:     [Wikipedia]   [Google]   [Baidu]   |
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Prentice Hall
Prentice Hall was an American major educational publisher owned by Savvas Learning Company. Prentice Hall publishes print and digital content for the 6–12 and higher-education market, and distributes its technical titles through the Safari Books Online e-reference service. History On October 13, 1913, law professor Charles Gerstenberg and his student Richard Ettinger founded Prentice Hall. Gerstenberg and Ettinger took their mothers' maiden names, Prentice and Hall, to name their new company. Prentice Hall became known as a publisher of trade books by authors such as Norman Vincent Peale; elementary, secondary, and college textbooks; loose-leaf information services; and professional books. Prentice Hall acquired the training provider Deltak in 1979. Prentice Hall was acquired by Gulf+Western in 1984, and became part of that company's publishing division Simon & Schuster. S&S sold several Prentice Hall subsidiaries: Deltak and Resource Systems were sold to National Education ... [...More Info...]       [...Related Items...]     OR:     [Wikipedia]   [Google]   [Baidu]   |
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William Moffitt
William E. Moffitt (9 November 1925 – 19 December 1958) was a British quantum chemist. He died after a heart attack following a squash match.Prof William Moffit, Obituaries, by Charles Coulson, The Times, 30 December 1958 page 8 He had been thought to be one of Britain's most gifted academics. Early life Moffitt was born in Berlin, Germany to British parents; his father was working in Berlin on behalf of the British government. He was educated by private tuition up to the age of 11. He attended Harrow School from 1936–43. His chemistry master later said of him that "he was undoubtably the most able of a decade of gifted boys ... ndhas a profound effect on all who met him. He did more than anyone to create in the school the intellectual climate so necessary for the stimulation of young minds". Academic career He then studied chemistry at New College, Oxford, under an open scholarship, and graduated with first class honours. His D.Phil. supervisor, Charles Coulson, later wrot ... [...More Info...]       [...Related Items...]     OR:     [Wikipedia]   [Google]   [Baidu]   |
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William Klyne
William Klyne (March 23, 1913, in Enfield, Middlesex – November 13, 1977) was an organic chemist known for his work in steroids and stereochemistry — a field in which he was a "pioneer", and in which Ernest Eliel and Norman Allinger described him as "one of the world's experts". Klyne taught at Westfield College, University of London, where he served as dean of science from 1971 to 1973, and as vice-principal from 1973 to 1976. He also served on the editorial board of the Biochemical Society from 1950 to 1955, and on IUPAC's nomenclature committee from 1971 until his death. As well, he established and maintained the Medical Research Council's Steroid Reference Collection, and wrote several textbooks, including ''The Chemistry of Steroids'' (1957) and ''Atlas of Stereochemical Correlations'' (1974). Personal life Klyne met Barbara Clayton in 1947 while both were employed at the Medical Research Council; they married in 1949. See also *Klyne–Prelog system In stereoch ... [...More Info...]       [...Related Items...]     OR:     [Wikipedia]   [Google]   [Baidu]   |
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Carl Djerassi
Carl Djerassi (October 29, 1923 – January 30, 2015) was an Austrian-born Bulgarian-American pharmaceutical chemist, novelist, playwright and co-founder of Djerassi Resident Artists Program with Diane Middlebrook, Diane Wood Middlebrook. He is best known for his contribution to the development of combined oral contraceptive pill, oral contraceptive pills,Ball P (2015) "Carl Djerassi", Nature (journal), Nature 519(7541), 34. nicknamed the "father of the pill". Early life Carl Djerassi was born in Vienna, Austria, but spent the first years of his infancy in Sofia, Bulgaria, the home of his father, Samuel Djerassi, a dermatologist and specialist in sexually transmitted diseases.Weintraub, Bob "Pincus, Djerassi and Oral Contraceptives" ''Chemistry in Israel'', Bulletin of the Israel Chemical Society. August 2005, pp. 47–50. His mother was Alice Friedmann, a Viennese dentist and physician. Both parents were History of the Jews in Europe, Jewish. Following his parents' divorce, Djer ... [...More Info...]       [...Related Items...]     OR:     [Wikipedia]   [Google]   [Baidu]   |
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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 enant ... [...More Info...]       [...Related Items...]     OR:     [Wikipedia]   [Google]   [Baidu]   |
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NMR Spectroscopy Of Stereoisomers
Nuclear magnetic resonance spectroscopy of stereoisomers most commonly known as NMR spectroscopy of stereoisomers is a chemical analysis method that uses NMR spectroscopy to determine the absolute configuration of stereoisomers. For example, the ''cis'' or ''trans'' alkenes, ''R'' or ''S'' enantiomers, and ''R,R'' or ''R,S'' diastereomers.Frank J. Hollis. "NMR Through the Looking Glass: Uses of NMR Spectroscopy in the Analysis and Synthesis of Chiral Pharmaceuticals." 1994/ref> In a mixture of enantiomers, these methods can help quantify the optical purity by integrating the area under the NMR peak corresponding to each stereoisomer. Accuracy of integration can be improved by inserting a chiral derivatizing agent with a nucleus other than hydrogen or carbon, then reading the heteronuclear NMR spectrum: for example fluorine-19 NMR or phosphorus-31 NMR. Mosher's acid contains a -CF3 group, so if the adduct has no other fluorine atoms, the 19F NMR of a racemic mixture shows just two ... [...More Info...]       [...Related Items...]     OR:     [Wikipedia]   [Google]   [Baidu]   |