16alpha-bromo-3beta-hydroxy-5alpha-androstan-17-one: a synthetic adrenal hormone that reduced the incidence of tuberculosis and other opportunistic infections in AIDS patients
Chemical reaction systems are typically regarded as having the Markov property -- they lack memory and their evolution depends only on their current state. Under a not-too-restrictive set of conditions, Markov chains will have a stationary distribution: the basic requirement seems to be that any state be reachable from any other in a finite number of steps. This seems like something that will generally be true for chemical systems, at least on the lattice of stoichiometrically-compatible states ...
July 2000. Background. Until 1999, DWI provided the support services for the voluntary approval system for chemicals used in swimming pool treatment. Following the decision to terminate the voluntary approval system, this study was commissioned in response to unresolved concerns about the conditions of approval for products based on the organobromine compound BCDMH.. Bromine-based disinfectants were introduced during the 1970s and early 1980s for use in recreational pools following the governments recommendation for the discontinuation of the use of chlorine gas. At the time, the perceived benefits of bromine were the improved bactericidal efficiency of bromination over chlorination (due to the greater biological activity of bromamines over chloramines, produced by the combination of the halogen with nitrogenous pollution - ie. urine), and the reduced scale of pH correction required, although it was recognized that elemental bromine is hazardous and capsulated dosing systems were recommended ...
Also known as 1-Bromopropane and n-propylbromide, nPB is an organobromine compound thats widely used as a solvent in several industries. nPB works great for the right applications, but it has a major downside: its reputation as a human carcinogen and a cause of other health problems in those who regularly apply it. To help educate our customers on solvent selection, we take a look at some of the most commonly asked questions regarding nPB as a carcinogen.. What evidence shows that nPB is a cancer causing agent?. The National Toxicology Program (NTP) considers nPB to be "reasonably anticipated to be a human carcinogen" [NTP 2013]. This assessment is based largely on animal studies in which rodents developed cancers of the lung, large intestine, and skin after being exposed to nPB in the air (i.e., nPB as a hazardous air pollutant). Evidence for nPB as a carcinogen is extrapolated from these studies and "anticipated" to have the same effect in humans.. How much nPB exposure does it take to cause ...
Terpenoid synthases produce a plethora of polycyclic natural products from only a few acyclic precursors. The mechanisms of these impressive enzyme-catalyzed polycyclization reactions have been discussed for decades, but a key unsanswered question is whether or not nonclassical carbocations - carbocations that contain delocalized 3-center 2-electron bonding arrays - are involved in these mechanisms. Nonclassical carbocations are common in nonpolar environments and have even been shown to persist in aqueous solution. It is reasonable, therefore, to think that they may also persist in enzyme active sites. In order to assess the stability of nonclassical carbocations in terpenoid synthase active sites, we are examining complexes of nonclassical species with small models of various protein residues - so-called theozymes. Some of the types of enzyme-nonclassical cation interactions that are possible are shown schematically above. We have so far shown that complexes between active site residues and ...
We present a detailed analysis of the anomalous carbocations: C2H5+ and C3H3+. This work involves (a) probing electronic structural properties, (b) ab initio dynamics simulations over a range of internal energies, (c) analysis of reduced dimensional potential surfaces directed along selected conformational t
View Notes - Lecture21outline from CHEM 0740 at Pittsburgh. I. Review Nucleophiles generally add to anomeric carbocations from the axial face This is a result of the anomeric effect that states that
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Electron affinity is the energy change associated with the addition of an electron to an atom or ion in the gas phase. For example, when an electron ...
Superhalogens belong to a class of molecules that not only mimic the chemistry of halogen atoms but also possess electron affinities that are much larger than that of chlorine, the element with the highest electron affinity in the periodic table. Using BO,sub,2,/sub, as an example and the synergy between density functional theory-based calculations and photoelectron spectroscopy experiments we demonstrate another unusual property of superhalogens. Unlike halogens, whose ability to accept an electron falls upon dimerization, B,sub,2,/sub,O,sub,4,/sub,, the dimer of BO,sub,2,/sub,, has an electron affinity larger than that of the BO,sub,2,/sub, building block. This ability of (BO,sub,2,/sub,),sub,2,/sub, and subsequent, higher oligomers (BO,sub,2,/sub,),sub,n,/sub, (n = 3 and 4), to retain their superhalogen characteristics can be traced to the enhanced bonding interactions between oxygen and boron atoms and due to the delocalization of the charge of the extra-electron over the terminal oxygen ...
Positive ion data are generally listed under the corresponding neutral species. With the exception of electron affinity data, negative ion data are provided under an entry for the anion. This means that if you want positive ion data, you must search for the neutral species, and if you want negative ion data you must search for the anion. This potentially confusing situation is a legacy of the format in which the data were collected and the fact that many of the anions in the database do not have corresponding neutral species. In those cases where the corresponding neutral is known, any electron affinity data will be listed under the neutral species, since the electron affinity may be considered a property of the neutral species. Heat of acidity data and heat of clustering data are considered Reaction Thermochemistry Data and are shown under the anion. In addition to the data described above, a link to search for appearance potential reactions with a product with the same formula as the current ...
Gutta, P.; Tantillo, D. J. Angew. Chem. Int. Ed. 2005, 44, 2719-2723: Proton Sandwiches: Nonclassical Carbocations with 4-Coordinate Protons. This article was highlighted in the Science Concentrates section of the May 2, 2005 issue of C&EN.. Bojin, M. D.; Tantillo, D. J. J. Phys. Chem. A 2006, 110, 4810-481: Nonclassical Carbocations as C-H Hydrogen Bond Donors Gutta, P.; Tantillo, D. J. J. Am. Chem. Soc. 2006, 128, 6172-6179: Theoretical Studies of Farnesyl Cation Cyclization: Pathways to Pentalenene. Hong, Y. J.; Tantillo, D. J. Org. Lett. 2006, 8, 4601-4604: Which is More Likely in Trichodiene Biosynthesis: Hydride or Proton Transfer?. Gutta, P.; Tantillo, D. J. Org. Lett. 2007, 9, 1069-1071: A Promiscuous Proton in Taxadiene Biosynthesis?. Willenbring, D.; Tantillo, D. J. Russ. J. Gen. Chem. 2008, 78, 723-731 (Rossiiskii Khimicheskii Zhurnal 2007, 51, 49-55): "Mechanistic Possibilities for Oxetane Formation in the Biosynthesis of Taxols D Ring". Lodewyk, M. W.; Gutta, P.; ...
A method of preparing a resinous system, and the resinous system produced by the method is described whereby 30 moles of formaldehyde, 2 moles catalyzing acid, 2 moles triethanolamine, and 12 moles of urea are sequentially reacted to provide an aqueous resinous solution. The resinous solution will cure at room temperature or upon application of heat, permitting its use as or in coatings, adhesives, and the like.
A hydride shift is a rearrangement of atoms in which an unstable carbocation is transformed into a more stable one. Carbocations are ions with positively charged carbon atoms and are often found in...
Nakagawa, Shigeki; Wei, Lan; Song, Won Min; Higashi, Takaaki; Ghoshal, Sarani; Kim, Rosa S.; Bian, C. Billie; Yamada, Suguru; Sun, Xiaochen; Venkatesh, Anu; Goossens, Nicolas; Bain, Gretchen; Lauwers, Gregory Y.; Koh, A. P.; El-Abtah, Mohamed; Ahmad, Noor B.; Hoshida, Hiroki; Erstad, Derek J.; Gunasekaran, Ganesh; Lee, Youngmin; Yu, Ming-Lung; Chuang, Wan-Long; Dai, Chia-Yen; Kobayashi, Masahiro; Kumada, Hiromitsu; Beppu, Toru; Baba, Hideo; Mahajan, Milind; Nair, Venugopalan D.; Lanuti, Michael; Villanueva, Augusto; Sangiovanni, Angelo; Iavarone, Massimo; Colombo, Massimo; Llovet i Bayer, Josep Maria; Subramanian, Aravind; Tager, Andrew M.; Friedman, Scott L.; Baumert, Thomas F.; Schwartz, Myron E.; Chung, Raymond T.; Tanabe, Kenneth K.; Zhang, Bin; Fuchs, Bryan C.; Hoshida, Yujin; Precision Liver Cancer Prevention Consortium ...
Gaines, A.F.; Kay, J.; Page, F.M., Determination of Electron Affinities. Part 8. - CCl4, CHCl3, and CH2Cl2, Trans. Farad. Soc., 1966, 62, 874, https://doi.org/10.1039/tf9666200874 . 7 matching species were found. For each matching species the following will be displayed: ...
Scientists in the US and China have invented a way to encapsulate teams of enzymes in a thin polymer shell. This enables the enzymes to carry out a series of sequential reactions
Organobromine compounds have a wide range of uses in the chemical industry, which vary from petrol additives and drilling fluids to dyestuffs and pharmaceuticals. The production of these compounds under more environmentally and industrially friendly conditions is desirable. In this work the ability of y-alumina and montmorillonite K10 to adsorb bromine onto the surface, and the ability of these adsorbed species to enhance bromination reactions, are investigated. These investigations include the bromination of the supports using, dibromomethane, hydrogen bromide and dibromine. The action of each of these individual reagents upon the supports results in its own distinct adsorbed bromine species on the surface. These investigations also include the hydrobromination of alkenes and the Hell Volhard Zelinsky reaction (bromination of the carbon a to the carboxylic acid group). The alkenes chosen for this work include 1,9-decadiene and butenes, as these give rise to both liquid and gas phase ...
Bromine, from ancient Greek, meaning "stench", is a chemical element with symbol Br, and atomic number 35. It is a halogen.. Free bromine does not occur in nature, but occurs as colorless soluble crystalline salts, analogous to table salt. The high solubility of bromide ions has caused its accumulation in the oceans, where it is abundantly available. Commercially, the element is easily extracted from brine pools, mostly in the United States, Israel and China.. Elemental bromine is a red-brown liquid at room temperature, corrosive and toxic, with properties between those of chlorine and iodine. One of the major uses of bromine is as a water purifier/disinfectant in swimming pools and hot tubs. Another key use of bromine compounds is in the manufacturing of pharmaceuticals: Brominated substances are important ingredients of many over-the-counter and prescription drugs, including analgesics, sedatives, and antihistamines.. Elestors storage systems incorporate a number of parallel and independent ...
Lewis base-bridged intermetallic compounds comprising the reaction product of a transition metal alkoxide with a reducing metal having a higher oxidation potential than the transition metal in the presence of a Lewis base and said reaction product being associated by coordinate covalent bridges formed from the Lewis base and composed of donor atoms selected from the group consisting of oxygen, nitrogen, sulfur and phosphorous; and catalyst components and systems for the polymerization of alpha olefins.
About 90 % of all ozone is found in a layer high up in the stratosphere. Detecting trends in this layer and the atmospheres total ozone content requires confidence in the characteristics of monitoring instruments, assurance in their performance and robust calibration methods to ensure data accuracy. Precise measurements over many years will be needed to detect ozone recovery processes, which are expected to occur after restrictions in the use of chlorine and bromine compounds were imposed by the 1987 Montreal Protocol.. Established networks for monitoring total column ozone, which is the ozone in an imaginary column between ground level and the top of the atmosphere, rely on bulky, ageing, or proprietary instruments. Each network operates one or more master instruments to which all other network instruments are referred to ensure measurements inter-relate. However different instrument types yield small, but significant, differences in output data, hampering this process and impeding the merging ...
Ion-implanted, shallow-energy, donor centres in diamond: the effect of negative electron affinity. Johan F. Prins Department of Physics, University of Pretoria, Pretoria 0002 Gauteng, South Africa. 4 th International Conference on: Slideshow 111078 by Roberta
A nitrogen-containing Lewis base mediated regioselective [4 + 2] cyclization strategy between allenic esters and α,β-unsaturated ketimines was discovered, affording a series of hydropyridine derivatives in moderate to good yields under mild conditions.
Our research interests involve the combined application of theory and experiment in structural-mechanistic studies. Our research work is centered on the generation and investigation of electron deficient carbocations by NMR spectroscopy, ab initio, DFT, IGLO and GIAO calculations. This include the structures of some of the most important carbocation intermediates, effects of heteroatoms on the stability of carbocations and their role in the electrophilic substitution reactions.. Our work is also concerned with the possible role of onium dications (superelectrophiles) in superacid catalyzed reactions. Some electrophiles, such as carboxonium ions, nitronium ion and related systems are capable of further interaction with Bronsted or Lewis superacids can be greatly activated in superacidic systems. Such further interactions produce superelectrophiles, which are highly reactive, energetic, high lying intermediates of dipositive nature. They are the de facto reactive intermediates (such as NO2H2+, ...
The ,-stabilized carbanion complexes [PhSO2CHCNNa·THF], 3, [t-BuSO2CHCNNa], 4, [PhSO2CHCNK], 5, [t-BuSO2CHCNK], 6, and [MeSO2CHCNLi·TMEDA], 7, have been synthesized via the metalation of the parent (organo)sulfonylacetonitriles by BuLi, BuNa, or BnK in THF solution (or THF/TMEDA in the case of 7). In addition, complexes 3 and 7 have been characterized by single-crystal X-ray analyses and have been found to adopt related structures in the solid state. Complex 7 is a molecular dimer containing a central 12-membered (OSCCNLi)2 ring core, with each metal rendered tetracoordinate by binding to a chelating TMEDA molecule. As found in related complexes, no direct carbanion to lithium contacts are present in the structure of 7. Complex 3 forms a polymeric cage structure composed of associated dimeric (OSCCNNa)2 rings, similar to those found in 7. The larger sodium cations, and the presence of only one THF molecule/metal, allow additional contacts with the anions, leading to hexacoordination at the ...
Two interesting questions are addressed in a focal-point computational study of t-butyl radical and the t-butyl anion from the Schaefer group.1 First, is the radical planar? EPR and PES studies from the 1970s indicate a pyramidal structure, with an inversion barrier of only 0.64 kcal mol-1. The CCSD(T)/cc-pCVTZ optimized structure of t-butyl radical shows it to be pyramidal with the out-of-plane angle formed by one methyl group and the other three carbons of 22.9°, much less than the 54.7° of a perfect tetrahedron. Focal point analysis give the inversion barrier 0.74 kcal mol-1, in outstanding agreement with experiment.. Second, what is the electron affinity (EA) of the t-butyl radical? Schleyer raised the concern that the alkyl anions may be unbound, and suggested that the electron affinity of t-butyl radical was -9.6 kcal mol-1; in other words, the anion is thermodynamically unstable. This focal-point study shows just how sensitive the EA is to computational method. The HF/CBS value of the ...
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Today is the birthday of Maria Sibylla Merian, born in Frankfurt, Germany in 1647. She was a VERY early explorer and explainer of botanical end entomological processes. I had never heard of her until I read about her at the Biodiversity Heritage Librarys blog site, where they write, Marias illustrations were important and revolutionary for a number…
The lighting setup was dictated by the choice of location. For the sequences captured in-studio, studio lighting was employed. As stated previously, the studio lighting setup consisted of 8 650W lights and an above head height frame suspended from the ceiling and a control panel that allowed the intensity of each light to be adjusted individually. In contrast, additional lighting in the on-location sites was more sparingly used. In fact, no additional lighting was used in the outdoor shots. For the indoor location, there was a limited amount of additional lighting provided by a 300W spot and a 4-bank Kino Flo lighting fixture [6]. The basic philosophy behind the studio lighting design was to illuminate the performance area from a single key light and two diffuse fill lights to soften shadows cast by the key. The diffuse lighting was provided by two of the 650W spot lights mounted at head height at either end (ie. left and right from the camera perspective) of the performance area, with a screen ...
Commonly used triethyl aluminum and tri-isobutyl aluminum cocatalysts may be replaced in olefin polymerizations with a cocatalyst conforming to the formula AlR z (X z ) n L z m wherein R z may be a linear or branched organic moiety having at least 5 carbons and X z may be a linear or branched organic moiety having at least 5 carbons or heteroatom substituted organic moiety or a heterocyclic moiety having at least 4 atoms and may be anionic (n=2) or dianionic (n=1). One X z may also be hydrogen. The aluminum complex may also be in the form of an adduct complex where L z may be a Lewis base and m=1−3. In the absence of a Lewis base, m=0.
It has previously been shown that self-consistent-charge density-functional tight-binding (SCC-DFTB) suffers from a self-interaction error that leads to artificial stabilization of delocalized states. The effects of the error are similar to those appearing for many density functionals. In SCC-DFTB, the delocalization error is inherently related to the use of a Hubbard-like term to describe on-site charge interactions. The mathematical simplicity of this Hubbard-like term makes it easy to estimate if a complex system is subject to artificial stabilization of delocalized states and to quantitatively predict the delocalization error in the system energy at large fragment separation. The error is directly proportional to the on-site charge interaction term but decreases as the fragments become more asymmetric. The difference in orbital energies required to eliminate the delocalization error becomes equal to the Hubbard-like parameter of the fragment with the highest electron affinity. However, in ...
Mikio Kumada, Executive Director & Global Strategist at LGT Capital Partners tells CNBCs Cash Flow why he thinks the market has overreacted to U.S. Federal Reserve Chairman Ben Bernankes comments.
Stradiņš J.; Glezer V.; Turovska B.; Markava E.; Freimanis J. Electrochemical reduction of N-aryl- and N-arylsulphonylbenzoquinoneimines in acetonitrile-II. Electron affinity and relationship between oxidation and reduction potentials. Electrochim Acta 1991, 36(7), 1219-1225 ...
Stradiņš J.; Glezer V.; Turovska B.; Markava E.; Freimanis J. Electrochemical reduction of N-aryl- and N-arylsulphonylbenzoquinoneimines in acetonitrile-II. Electron affinity and relationship between oxidation and reduction potentials. Electrochim Acta 1991, 36(7), 1219-1225 ...
My research involves investigations into the molecular genetics of a group of plant pathogenic Pseudomonads. This work involves studies of the genes responsible for the bacteria/plant interaction, investigation into pathogenicity islands present in these bacteria and study into the role of plasmids in the interaction between bacteria and plant ...
TY - JOUR. T1 - The electronic and geometrical structure of aluminum fluoride anions AlFn-, n=1-4, and electron affinity of their neutral parents. AU - Gutsev, Gennady. AU - Leś, Andrzej. AU - Adamowicz, Ludwik. PY - 1994/1/1. Y1 - 1994/1/1. N2 - The electronic and geometrical structure of AlF-, AlF 2-, AlF3-, and AlF4 - as well as their neutral parents are determined at the unrestricted Hartree-Fock (UHF) and second-order unrestricted Møller-Plesset (UMP2) levels of theory. The results of the calculations are used for estimating the adiabatic electron affinity (E.A.) of the neutrals and fragmentation energies of both the neutrals and anions. All these characteristics were also recomputed using the UMP2/6-31+G* geometry at the fourth-order UMP4 level of theory. According to the results of the single-, double, triple-, and quadruple-excitation fourth-order Møller-Plesset (MP4SDTQ) calculations, the AlF molecule in the ground state has no positive E.A., AlF2 possesses a rather high E.A. value ...
Kinetic measurements have been made at 25° C on the halogenation of benzoylacetone, acetylacetone, ethyl acetoacetate, ethyl α-bromoacetoacetate and diethyl bromomalonate. A method is described for analyzing the kinetic data and obtaining the rates of substitution of successive halogen atoms without isolating the partly halogenated derivatives. The reaction velocities measured are all independent of the halogen concentration, and represent the rates of ionization of the ketonic substances in presence of basic catalysts. The results obtained conform in general to the regularities previously found for this type of reaction, but anomalies are found in some instances; these are related to the interaction of large substituent groups in both substrate and anion catalyst. The effect of bromine substitution in increasing the reaction velocity is shown to decrease as the reactivity of the ketone increases, and this is explained in terms of the charge distribution in the anion of the substrate. ...
A Lewis acid is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any species that has a filled orbital containing an electron pair which is not involved in bonding but may form a dative bond with a Lewis acid to form a Lewis adduct. For example, NH3 is a Lewis base, because it can donate its lone pair of electrons. Trimethylborane (Me3B) is a Lewis acid as it is capable of accepting a lone pair. In a Lewis adduct, the Lewis acid and base share an electron pair furnished by the Lewis base, forming a dative bond.[1] In the context of a specific chemical reaction between NH3 and Me3B, the lone pair from NH3 will form a dative bond with the empty orbital of Me3B to form an adduct NH3•BMe3. The terminology refers to the contributions of Gilbert N. Lewis.[2]. The terms nucleophile and electrophile are more or less interchangeable with Lewis base and Lewis acid, respectively. However, ...
The BZ reaction is an example of a chemical oscillator, a system which instead of arriving at a steady state transitions between two different chemical states (which two states have two different colors, whence the waves above). Boris Belousov discovered it in the 1950s when he happened to mix together potassium bromate, cerium(IV) sulfate, propanedioic acid and citric acid in dilute sulfuric acid (hell, why not?); he made two attempts to publish his findings, but was rejected from peer-reviewed journals because he couldnt explain why the oscillations occurred ...
TY - JOUR. T1 - Dipole-bound anion of hydrogen fluoride dimer. T2 - Theoretical ab initio study. AU - Ramaekers, Riet. AU - Smith, Dayle M.A.. AU - Elkadi, Yasser. AU - Adamowicz, Ludwik. PY - 1997/10/3. Y1 - 1997/10/3. N2 - Ab initio calculations have been performed to determine the electron affinity of the hydrogen fluoride dimer, (HF)2. Although, a single hydrogen fluoride molecule does not form a stable stationary state with an excess electron, the hydrogen fluoride dimer has a positive electron affinity. In this system the excess electron is bound by the dipole field of the complex. The present theoretical calculations render the value of adiabatic electron affinity equal to 52 meV. The calculated value is in a good agreement with experimental result of 63 ± 6 meV of Bowen and coworkers.. AB - Ab initio calculations have been performed to determine the electron affinity of the hydrogen fluoride dimer, (HF)2. Although, a single hydrogen fluoride molecule does not form a stable stationary ...
A complex is a species in which the central atom is surrounded by a group of Lewis bases that have covalent bonds to the central atom. The Lewis bases that surround the central atom are generally referred to as ligands. Complexes are so named because when they were first studied, they seemed unusual and difficult to understand. Primarily, transition metals form complexes and their most observable property is their vivid color. The color of transition metal complexes is dependent on the identity and oxidation state of the central atom and the identity of the ligand.. Acids and bases were originally defined by Arrhenius as substances that donated protons (positively charged hydrogen ions) and hydroxide ions (consisting of one hydrogen atom bonded to one oxygen atom and having an overall charge of minus one) respectively. Subsequently, Bronsted and Lowry redefined acids and bases as being proton donors and proton acceptors, respectively. This broadened definition made it possible to include ...
A component of a polymerization catalyst is prepared by reacting an organo-magnesium compound, or a complex with an organo-aluminium compound, with an halogenating agent such as silicon tetrachloride or hydrogen chloride, and then reacting the product with a Lewis Base compound, particularly an ester and finally with titanium tetrachloride. The product obtained is combined with an organo-aluminium compound preferably together with a Lewis Base and used to polymerize an olefine monomer. The catalyst has a high activity and is stereospecific.
The test for alkenes is the bromine water test. The mechanism for this is the one with Br-Br. A solution of Br will be coloured orange, but when this reaction happens with an alkene, it will become colourless because it becomes a haloalkane. In the middle of this reaction, a carbocation (that is a cation of carbon) is formed; this is a C+. The position of this is important, depending on whether this is primary, secondary, or tertiary (see this page), determines the likelihood of different products being formed. A tertiary carbocation is the most stable, and therefore will form the major product, while secondary and primary carbocations will make the minor product ...
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Concepts: Hybridisation of carbon; σ and π-bonds; Shapes of simple organic molecules; Structural and geometrical isomerism; Optical isomerism of compounds containing up to two asymmetric centres, (R,S and E,Z nomenclature excluded); IUPAC nomenclature of simple organic compounds (only hydrocarbons, mono-functional and bi-functional compounds); Conformations of ethane and butane (Newman projections); Resonance and hyperconjugation; Keto-enoltautomerism; Determination of empirical and molecular formulae of simple compounds (only combustion method); Hydrogen bonds: definition and their effects on physical properties of alcohols and carboxylic acids; Inductive and resonance effects on acidity and basicity of organic acids and bases; Polarity and inductive effects in alkyl halides; Reactive intermediates produced during homolytic and heterolytic bond cleavage; Formation, structure and stability of carbocations, carbanions and free radicals. Preparation, properties and reactions of alkanes: ...
As the importance and abundance of silicon in our environment is large, it has been thought that silicon might take the place of carbon in forming a host of similar compounds and silicon-based life. However, until today there is no experimental evidence for such a hypothesis and carbon is still unique among the elements in the vast number and variety of compounds it can form. Also, the corresponding derivatives of the two elements show considerable differences in their chemical properties. The essential debate concerning organosilicon chemistry relates to the existence of the free planar tricoordinated silyl cations in condensed phase (R3Si+), in analogy to carbocations (R3C+) which have been known and characterized as free species. Although silyl cations are thermodynamically more stable than their carbon analogs, they are very reactive due to their high inherent electrophilicity and the ability of hypervalent coordination. On the other hand, stabilization by inductive and hyperconjugative ...
I have been doing chemistry since the mid fifties, since my first introduction to research as a summer student visitor at the Brookhaven Laboratory. (An earlier course in qualitative analysis came close in its demands for a chemist’s eye, hand brain coordination.) I’ll use this as an excuse to ruminate on the course of chemistry during those fifty years.. If you except biochemistry and, in particular, the DNA revolution, not much seemed to be happening from the fifties through the seventies, and my answer to friends’ queries about what was new in chemistry was often “not much!†My field â€" physical organic chemistry â€" was a victim of its own success. In a relatively few years, it had answered most of the important questions regarding reaction mechanisms and, by the sixties, was involved in heated arguments about classical versus non-classical carbocations â€" a question that could not be answered with the experimental techniques available at the ...
Abstract: Standard flavors of density-functional theory (DFT) calculations are known to fail in describing anions, due to large self-interaction errors. The problem may be circumvented by using localized basis sets of reduced size, leaving no variational flexibility for the extra electron to delocalize. Alternatively, a recent approach exploiting DFT evaluations of total energies on electronic densities optimized at the Hartree-Fock (HF) level has been reported, showing that the self-interaction-free HF densities are able to lead to an improved description of the additional electron, returning affinities in close agreement with the experiments. Nonetheless, such an approach can fail when the HF densities are too inaccurate. Here, an alternative approach is presented, in which an embedding environment is used to stabilize the anion in a bound configuration. Similarly to the HF case, when computing total energies at the DFT level on these corrected densities, electron affinities in very good ...
The elements of the periodic system with names, symbols, atomic numbers and weights, melting and boiling points, density, electronegativity and electron affinity, and electron configuration
reference: GSK-3-selective inhibitors derived from Tyrian purple indirubins., Meijer L, Skaltsounis AL, Magiatis P, Polychronopoulos P, Knockaert M, Leost M, Ryan XP, Vonica CA, Brivanlou A, Dajani R, Crovace C, Tarricone C, Musacchio A, Roe SM, Pearl L, Greengard P, Chem Biol 2003 Dec;10(12):1255-66. PMID: 14700633 ...