Chemical behavior

Studies other than preparative-type transformations have so far been limited to B-pyrazolylpyrazaboles. For example, the latter compounds have been found to react with R BX (where X is a readily leaving group) to form polynuclear boron spiro-cations (see Sect. V.A). It has also been shown that the pyrazolylpyrazaboles offer themselves as a class of neutral bidentate chelating ligands For example, the complexes H2B(pz)jB(pz)2ZnCl2 and Cl2Zn(pz)2B(pz)2B(pz)jZnCl2 were readily accessible by combination of the two reactants in an appropriate solvent. Obviously, a more detailed study of this feature is mandated. 

The rare earth elements are very electropositive, and, as a consequence, they generally form ionic compounds. Mineralogically, the REEs therefore form oxides, halides, carbonates, phosphates and silicates, borates or arsenates, but not sulphides. (Henderson 1996). Their oxidation states are given in Table 3.2. 

The following chapter includes information on the miscibility and the compatibility of liquified OF2 with elements and compounds at cryogenic temperatures. As pointed out by A. G. Streng (J. Chem. Eng. Data 16 [1971] 357/9), the data were based on comparatively short observation times and on the use of pure substances. At other conditions (e.g., catalytic amounts of impurities or higher temperatures) some of the mixtures may react slowly or violently. 

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Gr. aktis, aktinos, beam or ray). Discovered by Andre Debierne in 1899 and independently by F. Giesel in 1902. Occurs naturally in association with uranium minerals. Actinium-227, a decay product of uranium-235, is a beta emitter with a 21.6-year half-life. Its principal decay products are thorium-227 (18.5-day half-life), radium-223 (11.4-day half-life), and a number of short-lived products including radon, bismuth, polonium, and lead isotopes. In equilibrium with its decay products, it is a powerful source of alpha rays. Actinium metal has been prepared by the reduction of actinium fluoride with lithium vapor at about 1100 to 1300-degrees G. The chemical behavior of actinium is similar to that of the rare earths, particularly lanthanum. Purified actinium comes into equilibrium with its decay products at the end of 185 days, and then decays according to its 21.6-year half-life. It is about 150 times as active as radium, making it of value in the production of neutrons. 

The number of protons in an atom defines what element it is. For example carbon atoms have six protons, hydrogen atoms have one, and oxygen atoms have eight. The number of protons in an atom is referred to as the atomic number of that element. The number of protons in an atom also determines the chemical behavior of the element. 

A number of methods fill the valence of the interface atoms with an extra orbital, sometimes centered on the connecting MM atom. This results in filling out the valence while requiring a minimum amount of additional CPU time. The concern, which is dilficult to address, is that this might still affect the chemical behavior of the interface atom or even induce a second atom affect. 

To date, there have not been any large-scale comparisons of QM/MM methods in which many dilferent techniques were compared against experimental results for a large variety of chemical systems. There does tend to be some preference for the use of link atoms in order to ensure the correct chemical behavior of the QM region. Researchers are advised to consider the physical consequences of the effects that are included or excluded from various methods, as applied to their specific system. It is also prudent to verify results against experimental evidence when possible. 

This section is restricted to the general properties and chemical behavior of quaternary salts chiefly when they are used as dye intermediates (Tables IX-1-3, IX-4abc, IX-5) . 

It IS good chemical practice to represent molecules by their most stable Lewis structure The ability to write alternative resonance forms and to compare their relative stabilities however can provide insight into both molecular structure and chemical behavior This will become particularly apparent m the last two thirds of this text where the resonance concept will be used regularly... 

The carbon-halogen bonds of aryl halides are both shorter and stronger than the carbon-halogen bonds of alkyl halides In this respect as well as m their chemical behavior they resemble vinyl halides more than alkyl halides A hybridization effect seems to be responsible because as the data m Table 23 1 indicate similar patterns are seen for both carbon-hydrogen bonds and carbon-halogen bonds An increase m s... 

As written, equation 6.5 is a limiting law that applies only to infinitely dilute solutions, in which the chemical behavior of any species in the system is unaffected by all other species. Corrections to equation 6.5 are possible and are discussed in more detail at the end of the chapter. 

Ion exchange (qv see also Chromatography) is an important procedure for the separation and chemical identification of curium and higher elements. This technique is selective and rapid and has been the key to the discovery of the transcurium elements, in that the elution order and approximate peak position for the undiscovered elements were predicted with considerable confidence (9). Thus the first experimental observation of the chemical behavior of a new actinide element has often been its ion-exchange behavior—an observation coincident with its identification. Further exploration of the chemistry of the element often depended on the production of larger amounts by this method. Solvent extraction is another useful method for separating and purifying actinide elements. 

The study of the chemical behavior of concentrated preparations of short-Hved isotopes is compHcated by the rapid production of hydrogen peroxide ia aqueous solutions and the destmction of crystal lattices ia soHd compounds. These effects are brought about by heavy recoils of high energy alpha particles released ia the decay process. 

A. W. Frazier,. R. Lehr, and E. E. DiUard, Chemical Behavior of Eluorine in the Production of Wet-Process Phosphoric Acid, Bulletin Y-113, TVA, Muscle... 

Hafnium [7440-58-6] Hf, is in Group 4 (IVB) of the Periodic Table as are the lighter elements zirconium and titanium. Hafnium is a heavy gray-white metallic element never found free in nature. It is always found associated with the more plentiful zirconium. The two elements are almost identical in chemical behavior. This close similarity in chemical properties is related to the configuration of the valence electrons, and for zirconium and... 

E. M. Larsen, in H. J. Emelnus and A. F. Sharpe, eds.. Advances in Inorganic Chemistry and Radiochemisty, Academic Press, Inc., New York, 1988, pp. 92—97. Covers some aspects of chemical behavior of hafnium. 

The alkanes have low reactivities as compared to other hydrocarbons. Much alkane chemistry involves free-radical chain reactions that occur under vigorous conditions, eg, combustion and pyrolysis. Isobutane exhibits a different chemical behavior than / -butane, owing in part to the presence of a tertiary carbon atom and to the stability of the associated free radical. 

Dimeric aldoketenes and ketoketenes of P-lactone stmcture show a chemical behavior which is not much different to that of diketene. Thus nucleophiles add ia similar fashion to give derivatives of 3-ketoacids which are mono- or dialkylated at C-2 (aldo- and ketoketene dimers, respectively), but the reaction can often be slower than with the parent compound and, ia case of long-chain or bulky substituents, may not proceed at all. Other reactions can proceed differendy than those with diketene. For an overview of important reactions of aldoketene and ketoketene dimers see Reference 122. 

Separation Processes. The product of ore digestion contains the rare earths in the same ratio as that in which they were originally present in the ore, with few exceptions, because of the similarity in chemical properties. The various processes for separating individual rare earth from naturally occurring rare-earth mixtures essentially utilize small differences in acidity resulting from the decrease in ionic radius from lanthanum to lutetium. The acidity differences influence the solubiUties of salts, the hydrolysis of cations, and the formation of complex species so as to allow separation by fractional crystallization, fractional precipitation, ion exchange, and solvent extraction. In addition, the existence of tetravalent and divalent species for cerium and europium, respectively, is useful because the chemical behavior of these ions is markedly different from that of the trivalent species. 

The unique chemical behavior of KO2 is a result of its dual character as a radical anion and a strong oxidizing agent (68). The reactivity and solubiHty of KO2 is gready enhanced by a crown ether (69). Its usefiilness in furnishing oxygen anions is demonstrated by its appHcations in SN2-type reactions to displace methanesulfonate and bromine groups (70,71), the oxidation of benzyHc methylene compounds to ketones (72), and the syntheses of a-hydroxyketones from ketones (73). 

Potassium is required for enzyme activity in a few special cases, the most widely studied example of which is the enzyme pymvate kinase. In plants it is required for protein and starch synthesis. Potassium is also involved in water and nutrient transport within and into the plant, and has a role in photosynthesis. Although sodium and potassium are similar in their inorganic chemical behavior, these ions are different in their physiological activities. In fact, their functions are often mutually antagonistic. For example, increases both the respiration rate in muscle tissue and the rate of protein synthesis, whereas inhibits both processes (42). 

Silicon (3), which resembles metals in its chemical behavior, generally has a valence of +4. In a few compounds it exhibits a +2 valence, and in silicides it exists as a negative ion and largely violates the normal valency rules. Silicon, carbon, germanium, tin, and lead comprise the Group 14 (IVA) elements. Silicon and carbon form the carbide, SiC (see Carbides). Silicon and germanium are isomorphous and thus mutually soluble in all proportions. Neither tin nor lead reacts with silicon. Molten silicon is immiscible in both molten tin and molten lead. 

Oxo Ion Salts. Salts of 0x0 anions, such as nitrate, sulfate, perchlorate, iodate, hydroxide, carbonate, phosphate, oxalate, etc, are important for the separation and reprocessing of uranium, hydroxide, carbonate, and phosphate ions are important for the chemical behavior of uranium ia the environment (150—153). 

Vanadium(III) Chloride. Vanadium(III) chloride (vanadium trichloride, VCl ) is a pink-violet sohd, is readily hydrolyzed, and is insoluble in nonpolar solvents but dissolves in donor solvents, eg, acetonitrile, to form coordination compounds. Chemical behavior of the tribromide (VBr ) is similar to that of VCl. ... 

Zirconium tetrabromide [13777-25-8] ZrBr, is prepared direcdy from the elements or by the reaction of bromine on a mixture of zirconium oxide and carbon. It may also be made by halogen exchange between the tetrachloride and aluminum bromide. The physical properties are given in Table 7. The chemical behavior is similar to that of the tetrachloride. 

In its chemical behavior benzoic acid shows few exceptional properties the reactions of the carboxyl group are normal, and ring substitutions take place as would be predicted. 

X andjy are data matrices in row format, ie, the samples correspond to rows and the variables to columns. Some mathematical Hterature uses column vectors and matrices and thus would represent this equation as T = X. The purpose of rotation in general is to find an orientation of the points that results in enhanced understanding of the underlying chemical behavior of the system. 

Three-Dimensional Modeling of Chemical Structures. The two-dimensional representations of chemical stmctures are necessary to depict chemical species, but have limited utiHty in providing tme understanding of the effects of the three-dimensional molecule on properties and reactive behavior. To better describe chemical behavior, molecular modeling tools that reflect the spatial nature of a given compound are required. 

Most of the chemical properties of tritium are common to those of the other hydrogen isotopes. However, notable deviations in chemical behavior result from isotope effects and from enhanced reaction kinetics induced by the ( -emission in tritium systems. Isotope exchange between tritium and other hydrogen isotopes is an interesting manifestation of the special chemical properties of tritium. 

In the oxaziridines (1) ring positions 1, 2 and 3 are attributed to oxygen, nitrogen and carbon respectively. The latter almost always is in the oxidation state of a carbonyl compound and only in rare cases that of a carboxylic acid. Oxaziridinones are not known. The nitrogen can be substituted by aryl, alkyl, H or acyl the substituent causes large differences in chemical behavior. Fused derivatives (4), accessible from cyclic starting materials (Section 5.08.4.1), do not differ from monocyclic oxaziridines. 

Describe the chemical behavior of the and ozone concentration profiles of the St. Louis urban plume in Fig. 15-2. What is the reason for the sharp increase of b t and the sharp decrease of ozone in the vicinity of power plants ... 

A number of alkyl-substituted cyclobutadienes have been prepared by related methods Increasing alkyl substitution enhances the stability of the compounds. The tetra-/-butyl derivative is stable up to at least 150°C but is very reactive toward oxygen. This reactivity reflects the high energy of the HOMO. The chemical behavior of the cyclobutadienes as a group is in excellent accord with that expected from the theoretical picture of the structure of these compounds. 

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