Beta mechanisms

Keywords thiophene, methyl-thiophene, benzothiophene, H202, Ti-Beta, mechanism, XANES. 

Graphite exists in two forms alpha and beta. These have identical physical properties, except for their crystal structure. Naturally occurring graphites are reported to contain as much as 30% of the rhombohedral (beta) form, whereas synthetic materials contain only the alpha form. The hexagonal alpha type can be converted to the beta by mechanical treatment, and the beta form reverts to the alpha on heating it above lOOOoC. 

HyperChem quantum mechanics calculations must start with the number of electrons (N) and how many of them have alpha spins (the remaining electrons have beta spins). HyperChem obtains this information from the charge and spin multiplicity that you specify in the Semi-empirical Options dialog box or Ab Initio Options dialog box. N is then computed by counting the electrons (valence electrons in semi-empirical methods and all electrons in fll) mitio method) associated with each (assumed neutral) atom and... 

The Zn—A1 system permits manipulation of the mechanical properties by suitable heat treatment. The aluminum-rich alpha phase is especially suitable for solution hardening since it can be supersaturated by as much as 30 wt % zinc. Furthermore, both alpha and beta phases can be strengthened by precipitation because of decreasing solute solubiUty with decreasing temperature. 

Alpha—beta aluminum alloys respond to heat treatment with a general improvement of mechanical properties. Heat treatment is accompHshed by heating to 815—870°C, quenching in water, and reannealing at 370—535°C, depending on the size and section of the casting. Different combinations of strength, hardness, and ductility can be obtained. Some nickel in aluminum bronze is in soHd solution with the matrix and helps refine the precipitate, and a smaller amount is in the K-intermetaUic compound. 

This computation is also referred to as calculating the zinc equivalent of the alloy. The increase in strength in this alloy series is caused by increased amounts of beta phase in the stmcture. The silicon brasses show similar hardening effects accompanying a second phase. Typical mechanical properties and electrical conductivity for various cast alloys are shown in Table 2. 

W. J. Evans. Optimising mechanical properties in alpha + beta titanium alloys. Mater Sci Eng A 243 %%, 1998. 

In a few cases extensive cleavage of the substrate molecule occurs The case documented [JS] involves beta cleavage of tetramethylorthocarbonate and tri-methylorthoacetate The mechanism of this reaction involves the formation of a radical which can form a more stable radical by eliminating a stable molecule by beta cleavage Interestingly tetramethylorthocarbonate seems to suffer less cleav age by the LTG method [9] Examples of beta cleavage during direct fluorination are shown in equahons 6-9, where AF is aerosol direct fluorination procedure... 

Radioactive transformations are accomplished by several different mechanisms, most importantly alpha ptirticle, beta particle, tuid gamma ray emissions, Each of tliese mechanisms are sponuuieous nuclear transformations. The result of these transformations is tlie formation of different tuid more stable elements. 

Several different mechanisms, most importtuitly alplia particle, beta particle, and gamma ray emissions accomplish radioactive transformations. Each of these mechanisms is a spontaneous nuclear transformation. Tlie result of tliese transformations is the formation of different stable elements. Tlie kind of transformation that will ttike place for any given radioactive element is a function of the type of nuclear inslabilitv as well as the mass/energy relationship. The nuclear instability is dependent on the ratio of neutrons to... 

Michael reactions and, 895 Beta-keto ester, 851 alkylation of, 859-860 cyclic, 892-893 decarboxylation of, 857, 860 Michael reactions and. 895 pKd of, 852 synthesis of, 892-893 Beta-lactam antibiotics, 824-825 Beta oxidation pathway, 1133-1137 mechanism of, 1133-1136 Beta-pleated sheet (protein), 1038 molecular model of, 1039 secondary protein structure and, 1038-1039 Betaine, 720 Bextra. structure of, 544 BHA, synthesis of, 629 BHT, synthesis of. 629 Bicycloalkane. 129 Bijvoet. J. M., 299 Bimolecular, 363... 

There are three common ways by which nuclei can approach the region of stability (1) loss of alpha particles (a-decay) (2) loss of beta particles (/3-decay) (3) capture of an orbital electron. We have already encountered the first type of radioactivity, a-decay, in equation (/0). Emission of a helium nucleus, or alpha particle, is a common form of radioactivity among nuclei with charge greater than 82, since it provides a mechanism by which these nuclei can be converted to new nuclei of lower charge and mass which lie in the belt of stability. The actinides, in particular, are very likely to decay in this way. 

The term vitamin E describes a family of eight antioxidants, four tocopherols, alpha (a), beta ((3), gamma (y) and delta (8), and four tocotrienols (also a, (3, y, and 8). a-Tocopherol is present in nature in only one form, RRR a-tocopherol. The chemical synthesis of a-tocopherol results in eight different forms (SRR, SSR, SRS, SSS, RSR, RRS, RSS, RRR), only one of which is RRR a-tocopherol. These forms differ in that they can be right (R) or left (S) at three different places in the a-tocopherol molecule. RRR a-tocopherol is the only form of vitamin E that is actively maintained in the human body and is therefore the form of vitamin E found in the largest quantities in the blood and tissue. A protein synthesized in the liver (a-TTP alpha-tocopherol transfer protein) preferentially selects the natural form of vitamin E (RRR a-tocopherol) for distribution to the tissues. However, the mechanisms for the regulation of vitamin E in tissues are not known... 

Tinplate and Solder. Metallurgical studies were performed to determine the effect of irradiation at low temperature on the corrosion resistance of tinplate and on the mechanical properties and microstructure of tinplate and side-seam solder of the tinplate container. The area of major interest was the effect of low-temperature irradiation on the possible conversion of the tin from the beta form to the alpha form. In the case of pure tin, the transition occurs at 18 °C. It was feared that low-temperature irradiation would create dislocations in the crystal lattice of tin and enhance the conversion of tin from the silvery form to a powdery form rendering the tin coating ineffective in protecting the base steel. Tin used for industrial consumption contains trace amounts of soluble impurities of lead and antimony to retard this conversion for several years. 

According to quantum mechanics, an electron has two spin states, represented by the arrows T (up) and l(down) or the Greek letters a (alpha) and P (beta) We can think of an electron as being able to spin counterclockwise at a certain rate... 

A possible alternative mechanism for the formation of fragment alkyl ions comes immediately to mind—namely, beta fission of the Ci8 ion formed in Reactions 6 and 7 to form a smaller alkyl ion and an olefin. Thus we write as a typical example ... 

---