| 单词 | isomer |
| 例句 | The complex does not have any geometric isomers, but the mirror image is nonsuperimposable, so it has an optical isomer. Chemistry 2019-02-14T00:00:00Z Molecules must have a single bond to be cis- trans isomers. Biology for AP Courses 2022-06-09T00:00:00Z In Xu and co-workers’ synthetic pathway, a UV-induced chemical reduction occurs that leads to the strikingly selective destruction of these unwanted by-products, ultimately producing only the biologically relevant isomers of the purines. How DNA and RNA subunits might have formed to make the first genetic alphabet 2020-06-02T04:00:00Z Using mass spectrometry, researchers effectively identified glycan linkages, but in many instances failed to differentiate between sugar isomers. Exposed: cells’ sugary secrets 2020-03-15T04:00:00Z Moreover, the reactions are enantioselective: they produce one isomer of the reaction product to the near exclusion of the product’s mirror-image isomer. Practically simple reactions convert hydrocarbons to precious chemicals 2018-11-11T05:00:00Z Transition metal complexes often exist as geometric isomers, in which the same atoms are connected through the same types of bonds but with differences in their orientation in space. Chemistry 2019-02-14T00:00:00Z Geometric isomers, on the other hand, have similar placements of their covalent bonds but differ in how these bonds are made to the surrounding atoms, especially in carbon-to-carbon double bonds. Biology for AP Courses 2022-06-09T00:00:00Z The final product therefore comprises mostly one isomer in which the two appendages are fixed in what is known as a trans orientation to each other. Reaction combination opens up 3D molecular diversity for drug discovery 2018-08-05T04:00:00Z Water molecules were known to exist as two distinct "isomers", or types, based on their slightly different properties at the atomic level. Two different forms of water isolated 2018-05-30T04:00:00Z Chiral molecules can exist in two or more forms, called isomers, the structures of which are mirror images of one another. Therapeutic developments: Masters of medicine : Nature : Nature Research 2017-05-16T04:00:00Z Different geometric isomers of a substance are different chemical compounds. Chemistry 2019-02-14T00:00:00Z An isomerase is an enzyme that catalyzes the conversion of a molecule into one of its isomers. Biology for AP Courses 2022-06-09T00:00:00Z The separation factor is defined as the molar ratio of isomers in the permeate divided by the molar ratio of isomers in the feed. Ultra-selective high-flux membranes from directly synthesized zeolite nanosheets : Nature : Nature Research 2017-03-14T04:00:00Z The isomers of xylene are molecules with slight structural differences from each other that lead to different chemical properties. Seven chemical separations to change the world 2016-04-25T04:00:00Z Synthetic catalysts are not specific and typically produce a mix of isomers that must be painstakingly purified to yield a particular form. Therapeutic developments: Masters of medicine : Nature : Nature Research 2017-05-16T04:00:00Z In one isomer, cis chloride ligands cause more electron density on one side of the molecule than on the other, making it polar. Chemistry 2019-02-14T00:00:00Z In step two, citrate loses one water molecule and gains another as citrate is converted into its isomer, isocitrate. Biology for AP Courses 2022-06-09T00:00:00Z Often, only one of these isomers is clinically effective. Drugs that live long will prosper 2015-09-03T04:00:00Z The supply chains of many polymers, plastics, fibres, solvents and fuel additives depend on benzene, a cyclic hydrocarbon, as well as on its derivatives such as toluene, ethylbenzene and the xylene isomers. Seven chemical separations to change the world 2016-04-25T04:00:00Z Biological systems, however, such as the plant enzymes involved in opiate production, are adept at telling chiral isomers apart, making opioids good candidates for biosynthesis. Therapeutic developments: Masters of medicine : Nature : Nature Research 2017-05-16T04:00:00Z For the trans isomer, each ligand is directly across from an identical ligand, so the bond dipoles cancel out, and the molecule is nonpolar. Chemistry 2019-02-14T00:00:00Z One isomer is a poor disrupter of tubule activity while the other is extremely effective. Colourful chemotherapy 2015-07-09T04:00:00Z At the time it was revolutionary, but separating isomers quickly became standard practice among medicinal chemists, and thus eventually ceased to be patentable. Drugs that live long will prosper 2015-09-03T04:00:00Z Many biologically active compounds used in medicine and agriculture are still produced as a racemic mixture, even though only one isomer is actually active. [Perspective] A Two-Catalyst Photochemistry Route to Homochiral Rings 2014-04-29T14:56:12.328Z The easiest representation would be the tactile models built and produced by chemists to aid with their visualization and analysis of various chemical bonds and isomers in stereochemistry. The Science and Art of Diagramming: Culturing Life and Chemical Sciences, Part II 2013-04-05T12:45:00.527Z Draw the other geometric isomer and give its full name. Chemistry 2019-02-14T00:00:00Z Compounds with the same composition but different arrangements are called isomers. Scientists Probe Mystery Molecule that Reduces Greenhouse Gases 2012-01-16T16:15:01.960Z Others ban only specific isomers, opening the door to 'designer' drugs manufactured to mimic the effects but not the structure of an illegal compound. Poison in party pills is too much to swallow 2011-06-15T17:20:09.497Z When hydrolyzed under the influence of the enzyme cytase, it breaks down, first into cellobiose, an isomer of maltose, and then into glucose. The Chemistry of Plant Life The crude cresol obtained from tar cannot be separated into its different constituents by fractional distillation, since the boiling points of the three isomers are very close together. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 6 "Coucy-le-Château" to "Crocodile" When naming specific isomers, the descriptor is listed in front of the name. Chemistry 2019-02-14T00:00:00Z You don't have the foggiest notion of what an optical isomer is and you know it. A Feast of Demons Besides this oil, cloves also contain two neutral bodies, eugenin and caryophyllin, the latter of which is an isomer of camphor. Encyclopaedia Britannica, 11th Edition, Volume 6, Slice 5 "Clervaux" to "Cockade" The two pigments are, of course, isomers; but the difference in their structural arrangement is not known. The Chemistry of Plant Life Here we have assumed the substituent groups to be alike; when they are unlike, a greater number of isomers is possible. Encyclopaedia Britannica, 11th Edition, Volume 6, Slice 1 "Châtelet" to "Chicago" Optical isomers are very important in organic and biochemistry because living systems often incorporate one specific optical isomer and not the other. Chemistry 2019-02-14T00:00:00Z Technical benzene hexachloride is a mixture of several isomers, the gamma isomer being the most toxic to insects. Northern Nut Growers Association Report of the Proceedings at the 41st Annual Meeting Pleasant Valley, New York, August 28, 29 and 30, 1950 These hydrocarbons contain only a slight proportion of thiophene and its isomers, which can be removed only by a treatment with fuming sulphuric acid, but this is only exceptionally done. Encyclopaedia Britannica, 11th Edition, Volume 6, Slice 5 "Clervaux" to "Cockade" Many of the chemicals in food could exist in either of two forms, or isomers; they were chemically alike, but differently crystallized. Badge of Infamy In the case of tetra-substituted compounds, thirty isomers are possible when all the groups are different. Encyclopaedia Britannica, 11th Edition, Volume 6, Slice 1 "Châtelet" to "Chicago" The mirror images of the cis isomer form a pair of optical isomers, which have identical behavior except when reacting with other enantiomers. Chemistry 2019-02-14T00:00:00Z The practically pure isomer is known as lindane. Northern Nut Growers Association Report of the Proceedings at the 41st Annual Meeting Pleasant Valley, New York, August 28, 29 and 30, 1950 The oils drained from the crude naphthalene are re-distilled and worked for carbolic acid and its isomers. Encyclopaedia Britannica, 11th Edition, Volume 6, Slice 5 "Clervaux" to "Cockade" Sometimes either form was digestible, but frequently the body could use only the isomer to which it was adjusted. Badge of Infamy A factor of considerable importance in determining boiling-points of isomers is the symmetry of the molecule. Encyclopaedia Britannica, 11th Edition, Volume 6, Slice 1 "Châtelet" to "Chicago" Linkage isomers occur when the coordination compound contains a ligand that can bind to the transition metal center through two different atoms. Chemistry 2019-02-14T00:00:00Z The highest, the mammals, adhere to this diet for a considerable time; they live by the maternal milk, rich in casein, another isomer of albumen. Social Life in the Insect World Hence it was imperative to determine without doubt the molecular weight of some two typical isomers. Scientific American Supplement, No. 643, April 28, 1888 Martian plants produced different isomers from those on Earth. Badge of Infamy It is found that isomers have nearly the same critical volume, and that equal differences in molecular content occasion equal differences in critical volume. Encyclopaedia Britannica, 11th Edition, Volume 6, Slice 1 "Châtelet" to "Chicago" Explain why these two molecules are not isomers: Chemistry 2019-02-14T00:00:00Z I shall experiment with albumen, as provided by the egg of the hen; albumen being an isomer of fibrine, which is the principal element of all flesh diet. Social Life in the Insect World According to this view hyoscyamine ought to be the hyoscinate of hyoscine, or at any rate an isomer of this body. Scientific American Supplement, No. 324, March 18, 1882 Research designed to let the early colonists live off native food here had turned up an enzyme that enabled the body to handle either isomer. Badge of Infamy According to this view the active adenin obtained was not a contamination but an inactive isomer of the active substance. The Vitamine Manual Write the Lewis structure for each isomer of butane. Chemistry 2019-02-14T00:00:00Z It was found, however, that condensation products from the three isomers were distinguishable from one another neither in physical nor in tannoid properties. Synthetic Tannins The highest, the mammal, adheres to this diet for a long time: it has its mother's milk, rich in casein, another isomer of albumen. More Hunting Wasps Explain why these two molecules are not isomers: Chemistry 2019-02-14T00:00:00Z In a free state these nuclei possess the vitamine activity but under ordinary conditions are spontaneously transformed into isomers which do not possess an antineuritic power. The Vitamine Manual Write Lewis structures and name the five structural isomers of hexane. Chemistry 2019-02-14T00:00:00Z Isooctane is the common name of the isomer of C8H18 used as the standard of 100 for the gasoline octane rating: Chemistry 2019-02-14T00:00:00Z The addition made by my artifices shall be albumen, as found in the egg of the Hen, albumen the isomer of fibrin, which is the essential factor in any form of prey. More Hunting Wasps Write the structures for all the isomers of the –C5H11 alkyl group. Chemistry 2019-02-14T00:00:00Z Write the condensed structures of all isomers with the formula C2H6O2. Chemistry 2019-02-14T00:00:00Z Name and write the structures of all isomers of the propyl and butyl alkyl groups. Chemistry 2019-02-14T00:00:00Z Write the Lewis structures of all isomers with the formula C3H7ON that contain an amide linkage. Chemistry 2019-02-14T00:00:00Z There are also various types of spatial isomers, in which the relative orientations of the atoms in space can be different. Chemistry 2019-02-14T00:00:00Z When structures of butene are drawn with 120° bond angles around the sp2-hybridized carbon atoms participating in the double bond, the isomers are apparent. Chemistry 2019-02-14T00:00:00Z The different geometries produce different physical properties, such as boiling point, that may make separation of the isomers possible: Chemistry 2019-02-14T00:00:00Z Write the condensed structures of both isomers with the formula C2H6O. Chemistry 2019-02-14T00:00:00Z When they are cis, there will also be an optical isomer. Chemistry 2019-02-14T00:00:00Z Another important type of isomers are optical isomers, or enantiomers, in which two objects are exact mirror images of each other but cannot be lined up so that all parts match. Chemistry 2019-02-14T00:00:00Z Optical isomers differ only in the way they affect polarized light and how they react with other optical isomers. Chemistry 2019-02-14T00:00:00Z These two isomers will react differently with other optical isomers. Chemistry 2019-02-14T00:00:00Z In all cases, these are the cis isomers and never the trans isomers. Chemistry 2019-02-14T00:00:00Z The trans isomer, formed when the chlorines are positioned at a 180° angle, has very different properties from the cis isomers. Chemistry 2019-02-14T00:00:00Z Draw two other possible isomers in which the chlorine atom replaces a different hydrogen atom attached to the aromatic ring: Chemistry 2019-02-14T00:00:00Z Constitutional isomers have the same molecular formula but different spatial arrangements of the atoms in their molecules. Chemistry 2019-02-14T00:00:00Z Lewis structures that look different may actually represent the same isomers. Chemistry 2019-02-14T00:00:00Z Four carbon atoms in the chain of butene allows for the formation of isomers based on the position of the double bond, as well as a new form of isomerism. Chemistry 2019-02-14T00:00:00Z In a set of geometric isomers, the same types of atoms are attached to each other in the same order, but the geometries of the two molecules differ. Chemistry 2019-02-14T00:00:00Z Geometric isomers of alkenes differ in the orientation of the groups on either side of a bond. Chemistry 2019-02-14T00:00:00Z This makes it possible to have two isomers of 2-butene, one with both methyl groups on the same side of the double bond and one with the methyl groups on opposite sides. Chemistry 2019-02-14T00:00:00Z |
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