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19F NMR
Fluorine-19 nuclear magnetic resonance spectroscopy (fluorine NMR or 19F NMR) is an analytical technique used to detect and identify fluorine-containing compounds. 19F is an important nucleus for NMR spectroscopy because of its receptivity and large chemical shift dispersion, which is greater than that for proton nuclear magnetic resonance spectroscopy. Operational details 19F has a nuclear spin (I) of and a high gyromagnetic ratio. Consequently, this isotope is highly responsive to NMR measurements. Furthermore, 19F comprises 100% of naturally occurring fluorine. The only other highly sensitive spin NMR-active nuclei that are monoisotopic (or nearly so) are 1H and 31P. Indeed, the 19F nucleus is the third most receptive NMR nucleus, after the 3H nucleus and 1H nucleus. The 19F NMR chemical shifts span a range of ''ca.'' 800 ppm. For ''organo''fluorine compounds the range is narrower, being ''ca.'' -50 to -70 ppm (for CF3 groups) to -200 to -220 ppm (for CH2F groups). Th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
CFCl3
Trichlorofluoromethane, also called freon-11, CFC-11, or R-11, is a chlorofluorocarbon (CFC). It is a colorless, faintly ethereal, and sweetish-smelling liquid that boils around room temperature. CFC-11 is a Class 1 ozone-depleting substance which damages Earth's protective stratospheric ozone layer. Historical use Trichlorofluoromethane was first widely used as a refrigerant. Because of its high boiling point (compared to most refrigerants), it can be used in systems with a low operating pressure, making the mechanical design of such systems less demanding than that of higher-pressure refrigerants R-12 or R-22. Trichlorofluoromethane is used as a reference compound for fluorine-19 NMR studies. Trichlorofluoromethane was formerly used in the drinking bird novelty, largely because it has a boiling point of . The replacement, dichloromethane, boiling point , requires a higher ambient temperature to work. Prior to the knowledge of the ozone depletion potential of chlor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Contrast Agent
A contrast agent (or contrast medium) is a substance used to increase the contrast of structures or fluids within the body in medical imaging. Contrast agents absorb or alter external electromagnetism or ultrasound, which is different from radiopharmaceuticals, which emit radiation themselves. In x-rays, contrast agents enhance the radiodensity in a target tissue or structure. In MRIs, contrast agents shorten (or in some instances increase) the relaxation times of nuclei within body tissues in order to alter the contrast in the image. Contrast agents are commonly used to improve the visibility of blood vessels and the gastrointestinal tract. Several types of contrast agent are in use in medical imaging and they can roughly be classified based on the imaging modalities where they are used. Most common contrast agents work based on X-ray attenuation and magnetic resonance signal enhancement. Radiocontrast media For radiography, which is based on X-rays, iodine and barium are the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magnetic Resonance Imaging
Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio waves to generate images of the organs in the body. MRI does not involve X-rays or the use of ionizing radiation, which distinguishes it from CT and PET scans. MRI is a medical application of nuclear magnetic resonance (NMR) which can also be used for imaging in other NMR applications, such as NMR spectroscopy. MRI is widely used in hospitals and clinics for medical diagnosis, staging and follow-up of disease. Compared to CT, MRI provides better contrast in images of soft-tissues, e.g. in the brain or abdomen. However, it may be perceived as less comfortable by patients, due to the usually longer and louder measurements with the subject in a long, confining tube, though "Open" MRI designs mostly relieve this. Additionally, implants and oth ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acetone-d6
Deuterated acetone ((CD3)2CO), also known as Acetone-D6, is a form (called an isotopologue) of acetone (CH3)2CO in which the hydrogen atom ("H") is replaced with deuterium (heavy hydrogen) isotope ("D"). Deuterated acetone is a common solvent used in NMR spectroscopy. Properties As with all deuterated compounds, the properties of deuterated acetone are virtually identical to those of regular acetone. Manufacture Deuterated acetone is prepared from heavy water, D2O, by what amounts to an aldol reaction. In this case, the base used is a deuterated version of lithium hydroxide Lithium hydroxide is an inorganic compound with the formula LiOH. It can exist as anhydrous or hydrated, and both forms are white hygroscopic solids. They are soluble in water and slightly soluble in ethanol. Both are available commercially. While ...:P. J. Paulsen, W. D. Cooke. ''. Anal. Chem.'', 1963, 35 (10), pp 1560–1560. DOI: 10.1021/ac60203a072 In order to fully deuterate the acetone, the p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
C6D6
Deuterated benzene (C6D6) is an isotopologue of benzene (C6H6) in which the hydrogen atom ("H") is replaced with deuterium (heavy hydrogen) isotope ("D"). Properties The properties of deuterated benzene are very similar to those of normal benzene, however, the increased atomic weight of deuterium relative to protium means that the melting point of C6D6 is about 1.3 °C higher than that of the nondeuterated analogue. The boiling points of both compounds, however, are the same: 80 °C. Applications Deuterated benzene is a common solvent used in NMR spectroscopy. It is widely used for taking spectra of organometallic compounds, which often react with the cheaper deuterated chloroform. A slightly more exotic application of C6D6 is in the synthesis of molecules containing a deuterated phenyl group. Deuterated benzene will undergo all the same reactions its normal analogue will, just a little more slowly due to the kinetic isotope effect. For example, deuterated benzene could ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
CDCl3
Deuterated chloroform, also known as chloroform-''d'', is the organic compound with the formula C2HCl3 or . Deuterated chloroform is a common solvent used in NMR spectroscopy. The properties of are virtually identical. Preparation Deuterated chloroform is commercially available. It is more easily produced and less expensive than deuterated dichloromethane. Deuterochloroform is produced by the reaction of hexachloroacetone with deuterium oxide, using pyridine as a catalyst. The large difference in boiling points between the starting material and product facilitate purification by distillation. : NMR solvent In proton NMR spectroscopy, deuterated solvent (enriched to >99% deuterium) is typically used to avoid recording a large interfering signal or signals from the proton(s) (i.e., hydrogen-1) present in the solvent itself. If nondeuterated chloroform (containing a full equivalent of protium) were used as solvent, the solvent signal would almost certainly overwhelm and obscure any ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
CF3CO2H
Trifluoroacetic acid (TFA) is an organofluorine compound with the chemical formula CF3CO2H. It is a structural analogue of acetic acid with all three of the acetyl group's hydrogen atoms replaced by fluorine atoms and is a colorless liquid with a vinegar-like odor. TFA is a stronger acid than acetic acid, having an acid ionisation constant, ''K''a, that is approximately 34,000 times higher, as the highly electronegative fluorine atoms and consequent electron-withdrawing nature of the trifluoromethyl group weakens the oxygen-hydrogen bond (allowing for greater acidity) and stabilises the anionic conjugate base. TFA is widely used in organic chemistry for various purposes. Synthesis TFA is prepared industrially by the electrofluorination of acetyl chloride or acetic anhydride, followed by hydrolysis of the resulting trifluoroacetyl fluoride: : + 4 → + 3 + : + → + Where desired, this compound may be dried by addition of trifluoroacetic anhydride. An older route t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
C6F6
Hexafluorobenzene, HFB, , or perfluorobenzene is an organic, aromatic compound. In this derivative of benzene all hydrogen atoms have been replaced by fluorine atoms. The technical uses of the compound are limited, although it is recommended as a solvent in a number of photochemical reactions. In the laboratory hexafluorobenzene is used as standard in fluorine-19 NMR spectroscopy, solvent and standard in carbon-13 NMR, solvent in proton NMR, solvent when studying some parts in the infrared and solvent in ultraviolet–visible spectroscopy, as hexafluorobenzene itself hardly shows any absorbance in the UV region. Geometry of the aromatic ring Hexafluorobenzene stands somewhat aside in the perhalogenbenzenes. When counting for bond angles and distances it is possible to calculate the distance between two ortho fluorine atoms. Also the non bonding radius of the halogens is known. The following table presents the results: The conclusion of the table is hexafluorobenzene is the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Trifluorotoluene
Trifluorotoluene is an organic compound with the formula of C6H5CF3. This colorless fluorocarbon is used as a specialty solvent in organic synthesis and an intermediate in the production of pesticides and pharmaceuticals.Banks, R.E. Organofluorine Chemicals and their Industrial Applications, Ellis Horwood LTD, Chichester, 1979. Synthesis For small-scale laboratory preparations, trifluorotoluene is synthesized by coupling an aromatic halide and trifluoromethyl iodide in the presence of a copper catalyst: :PhX + CF3I → PhCF3 (where X = I, Br) Industrial production is done by reacting benzotrichloride with hydrogen fluoride in a pressurized reactor.Siegemund, Günter "Aromatic Compounds with Fluorinated Side-Chains" in Ullmann’s Encyclopedia of Industrial Chemistry 2005, Wiley-VCH. . :PhCCl3 + 3 HF → PhCF3 + 3 HCl Uses Trifluorotoluene has a variety of niche uses. Low toxicity alternative to dichloromethane According to Ogawa and Curran, trifluorotoluene is similar to dich ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
C6H5F
Fluorobenzene is the chemical compound with the formula C6H5F, often abbreviated PhF. A colorless liquid, it is a precursor to many fluorophenyl compounds. Preparation PhF was first reported in 1886 by O. Wallach at the University of Bonn, who prepared the compound in two steps. Phenyldiazonium chloride was first converted to a triazene using piperidine: : hN2l + 2 (CH2)5NH → PhN=N-N(CH2)5 + CH2)5NH2l The triazine was then cleaved with hydrofluoric acid: :PhN=N-N(CH2)5 + 2 HF → PhF + N2 + CH2)5NH2 Historical note: in Wallach's era, the element fluorine was symbolized with "Fl". Thus, his procedure is subtitled "Fluorbenzol, C6H5Fl". On the laboratory scale, PhF is prepared by the thermal decomposition of the benzenediazonium tetrafluoroborate: :PhN2BF4 → PhF + BF3 + N2 According to the procedure, solid hN2F4 is heated with a flame to initiate an exothermic reaction, which also affords boron trifluoride and nitrogen gas. Product PhF and BF3 a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isotopes Of Thulium
Naturally occurring thulium (69Tm) is composed of one stable isotope, 169Tm (100% natural abundance). Thirty-four radioisotopes have been characterized, with the most stable being 171Tm with a half-life of 1.92 years, 170Tm with a half-life of 128.6 days, 168Tm with a half-life of 93.1 days, and 167Tm with a half-life of 9.25 days. All of the remaining radioactive isotopes have half-lives that are less than 64 hours, and the majority of these have half-lives that are less than 2 minutes. This element also has 26 meta states, with the most stable being 164mTm (t1/2 5.1 minutes), 160mTm (t1/2 74.5 seconds) and 155mTm (t1/2 45 seconds). The isotopes of thulium range in atomic weight from 144.97007 u (145Tm) to 178.95534 u (179Tm). The primary decay mode before the most abundant stable isotope, 169Tm, is electron capture, and the primary mode after is beta emission. The primary decay products before 169Tm are erbium isotopes, and the primary products after are ytterbium isotope ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
