Boron behavioral effect

On the theoretical side, study of the dissociation of addition compounds of amines with trimethylborane, boron trifluoride, and borane provide a new quantitative approach to steric strains. These studies quickly removed doubts as to the importance of steric effects in chemical behavior. 

It is necessary for the intermediate cation or complex to bear considerable car-bocationic character at the carbon center in order for effective hydride transfer to be possible. By carbocationic character it is meant that there must be a substantial deficiency of electron density at carbon or reduction will not occur. For example, the sesquixanthydryl cation l,26 dioxolenium ion 2,27 boron-complexed imines 3, and O-alkylated amide 4,28 are apparently all too stable to receive hydride from organosilicon hydrides and are reportedly not reduced (although the behavior of 1 is in dispute29). This lack of reactivity by very stable cations toward organosilicon hydrides can enhance selectivity in ionic reductions. 

Whitworth, M.R., G.W. Pendleton, D.J. Hoffman, and M.B. Camardese. 1991. Effects of dietary boron and arsenic on the behavior of mallard ducklings. Environ. Toxicol. Chem. 10 911-916. 

It is well known that the elements in framework of zeolite molecular sieves greatly influence the properties and behaviors of these materials [1-3], The introduction of heteroatoms into the framework has become one of most active fields in study of zeolites. The investigations were mostly focused on the methods to introduce heteroatoms into the framework (for examples, hydrothermal synthesis and post-synthesis), the mechanisms for incorporations, the effect of heteroatoms on the acid-base properties and the catalytic features of modified samples [1-10]. Relatively less attention was paid to the effect of treatment process on the porous properties of samples although the incorporation of heteroatoms, especially by the so-called post-synthesis, frequently changes the distribution of pore size. Recently, we incorporated Al, Ga and B atoms into zeolites (3 by the post-synthesis in an alkaline medium named alumination, galliation and boronation, respectively. It was found that different trivalent elements inserted into the [3 framework at quite different level. The heteroatoms with unsuitable atom size and poor stability in framework were less introduced, leading to that a considerable amount of framework silicon were dissolved under the action of base and the mesopores in zeolite crystal were developed. As a typical case, the boronation of zeolites (3 and the accompanied formation of mesopores are reported in the present paper. 

LEWIS ACID. Any molecule or ion (culled and electrophilel that can combine with another molecule or ion by lomtiog a covalent bond with two electrons I rum the second molecule or ion. An acid is thus an electron acceptor. Hydrogen ion (proton) is the simplest substance that will do ihis. but many compounds such as boron trilluuricJe. Bt . nod aluminum chloride. AlCIv. exhibit the same behavior and are therefore properly called adds. Such substances show acid effects on indicator colors and when dissolved in the proper solvents. 

AP-CVD ZnO Hu and Gordon [10,28] observed an increase of electron mobility p with increasing film thickness d, both for boron-doped and for gallium-doped AP-CVD ZnO films, with a more pronounced slope for small thickness. They attributed this behavior to the influence of the grain boundary scattering effect, which is dominant for thinner films that are composed of smaller crystallites. 

The reaction of XIII with EtOH in CHjCl EtOH, in 1 1 molar ratio, affords the ethoxy-derivative, [8,8-(q2-dppp)-9-(OEt)-nido-RhSB,H,] (XIV) behavior which is seen in the series of related compounds.12,111 This suggests that the boron vertex at the 9-position in Xm, and the related series of compounds, is prone to nucleophilic substitution reactions. XIV was characterized by NMR spectroscopy, mass spectrometry and X-ray diffraction. In contrast to the parent rhodathiaborane IV, and XIII, compound XIV does not feature fluxional behavior, even at 373 K implying, perhaps, AG values greater than 64 kjmol 1 for a possible dynamic process in XIV. The apparent large difference in the activation energy for the substituted versus the unsubstituted species may be due to either electronic or steric effects. The differences in the structures of XIII and XIV are minimal except for the B(9)-B(10) distances which differ by 0.083 A.4b This tends to suggest a role for this bond in the fluxional process although a purely steric influence of the substituent at the 9-position in XIV cannot be ruled out. 

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