In boron

Riter J R Jr 1973 Shock-induced graphite.far.wurtzite phase transformation in boron nitride and implications for stacking graphitic boron nitride J. Chem. Phys. 59 1538... 

Boranes are typical species with electron-deficient bonds, where a chemical bond has more centers than electrons. The smallest molecule showing this property is diborane. Each of the two B-H-B bonds (shown in Figure 2-60a) contains only two electrons, while the molecular orbital extends over three atoms. A correct representation has to represent the delocalization of the two electrons over three atom centers as shown in Figure 2-60b. Figure 2-60c shows another type of electron-deficient bond. In boron cage compounds, boron-boron bonds share their electron pair with the unoccupied atom orbital of a third boron atom [86]. These types of bonds cannot be accommodated in a single VB model of two-electron/ two-centered bonds. 

Figure 2-60. Soine examples of electron-deficient bonds a) diborane featuring B-H-B bonds b) diborane in a tentative RAMSES representation c) the orbital in a B-B-B bond (which occurs in boron cage compounds),...

The element is not found free in nature, but occurs as orthoboric acid usually found in certain volcanic spring waters and as borates in boron and colemantie. Ulexite, another boron mineral, is interesting as it is nature s own version of "fiber optics."... 

Verify that the formal charges on boron and oxy gen in boron trifluoride etherate are correct... 

The boron atom in boron trifluoride is hybridized to the sp planar configuration and consequently is coordinatively unsaturated, ie, a Lewis acid. Its chemistry centers around satisfying this unsaturation by the formation with Lewis bases of adducts that are nearly tetrahedral sp [ The electrophilic properties (acid strengths) of the trihaloboranes have been found to increase in the order BF < BCl < BBr < BI (3,4). 

In the case of the fibrous laminate not much work has been done, but it has been observed that a significant loss of stiffness in boron—aluminum laminate occurs when cycled in tension—tension (43,44). Also, in a manner similar to that in the laminated PMCs, the ply stacking sequence affects the fatigue behavior. For example, 90° surface pHes in a 90°/0° sequence develop damage more rapidly than 0° pHes. In the case of laminates made out of metallic sheets, eg, stainless steel and aluminum, further enhanced resistance against fatigue crack propagation than either one of the components in isolation has been observed (45). 

Boron s electron deficiency does not permit conventional two-electron bonds. Boron can form multicenter bonds. Thus the boron hydrides have stmctures quite unlike hydrocarbons. The B nucleus, which has a spin of 3/2, which has been employed in boron nuclear magnetic resonance spectroscopy. 

Production from sodium borate ores takes place in the United States, Turkey, and Argentina. AH U.S. production based on sodium borate ores is from the United States Borax Chemical Corp. in Boron, California. Turkish mining of tincal takes place at Kirka. This operation is under the control of the Turkish government and its representative, Etibank. Argentine production is carried out at Tincalayu, primarily by Boroquimica Samicaf. 

Various borate esters are chemostetilants for house flies (51). Tributyl borate, available from Eagle-Picher, Miami, Oklahoma, which is isotopically enriched in boron-10, is being used as a chemical precursor in the synthesis of pharmacologically active boron compounds suitable for boron neutron capture therapy. 

Amine boranes have been examined by a variety of spectroscopic methods (24—29). The boron-substituted alpha-amino acids have been utilized in animal model studies. These compounds along with their precursors and selected derivatives have been shown to possess antineoplastic, antiarthritic, and hypolipidemic activity (30—32). The boron amino acid analogues are also being evaluated for possible utility in boron neutron capture therapy (BNCT) (33). 

Fig. 2.30. SAM map offractured SiC after sintering with B addition [2.167], (a)-(d) elemental maps in boron, potassium, sodium, and oxygen, respectively. (E), (F) point analyses at points A and B, respectively.

We can consider the hydroboration step as though it involved borane (BH3). It simplifies our mechanistic analysis and is at variance with reality only in matters of detail. Borane is electrophilic it has a vacant 2p orbital and can accept a pair- of electrons into that orbital. The source of this electron pair is the tt bond of an alkene. It is believed, as shown in Figure 6.10 for the example of the hydroboration of 1-methylcyclopentene, that the first step produces an unstable intenrrediate called a tt complex. In this tt complex boron and the two carbon atoms of the double bond are joined by a three-center two-electron bond, by which we mean that three atoms share two electrons. Three-center two-electron bonds are frequently encountered in boron chemistry. The tt complex is fonrred by a transfer of electron density from the tt orbital of the alkene to the 2p orbital... 

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