Electronic bonding data

TABLE 2 Structure and Electronic Bonding Data for the a-C H Models, in Comparison with Experimentally Determined Values... 

Optical absorption measurements give band-gap data for cubic sihcon carbide as 2.2 eV and for the a-form as 2.86 eV at 300 K (55). In the region of low absorption coefficients, optical transitions are indirect whereas direct transitions predominate for quantum energies above 6 eV. The electron affinity is about 4 eV. The electronic bonding in sihcon carbide is considered to be predominantiy covalent in nature, but with some ionic character (55). In a Raman scattering study of vahey-orbit transitions in 6H-sihcon carbide, three electron transitions were observed, one for each of the inequivalent nitrogen donor sites in the sihcon carbide lattice (56). The donor ionization energy for the three sites had values of 0.105, 0.140, and 0.143 eV (57). 

The structures of the series trans-Pt(PMePh2)2 RC1 (R = Me, CF2CF3) show Pt-C bonds of 2.081 and 2.013 A, respectively, with the electron-withdrawing fluoroalkyl leading to a shorter and stronger bond. (Data for some other platinum alkyls are discussed in section 3.8.10.)... 

Table 2.4 shows a comparison of the experimental and PPP-MO calculated electronic spectral data for azobenzene and the three isomeric monoamino derivatives. It is noteworthy that the ortho isomer is observed to be most bathochromic, while the para isomer is least bathoch-romic. From a consideration of the principles of the application of the valence-bond approach to colour described in the previous section, it might have been expected that the ortho and para isomers would be most bathochromic with the meta isomer least bathochromic. In contrast, the data contained in Table 2.4 demonstrate that the PPP-MO method is capable of correctly accounting for the relative bathochromicities of the amino isomers. It is clear, at least in this case, that the valence-bond method is inferior to the molecular orbital approach. An explanation for the failure of the valence-bond method to predict the order of bathochromicities of the o-, m- and p-aminoazobenzenes emerges from a consideration of the changes in 7r-electron charge densities on excitation calculated by the PPP-MO method, as illustrated in Figure 2.14. 

Ill37-42 lists the electronic absorption data for doubly bonded germanium compounds. 

Reduction of bulky organohalogermylenes leads to the formation of pentametallic germanium clusters 149 and 150 (Equations (260) and (261), respectively).322 The structure of 149 is shown in Figure 8, and selected structural data are collected in Table 32. The five germanium atoms are held together by six two-center, two-electron bonds, and a lone pair resides on the unsubstituted Ge(5) atom. 

Fig. 39). The ESR data for dimethylselenide dimer cation radical 107c are consistent with two-center three-electron bonding, in which two electrons are in a cr bond between the two chalcogens, while the third electron is in a o orbital. 

The effect of substituent groupings upon the first ionization potential of, at least, the aliphatic aldehydes and ketones does not seem to provide clear evidence for a choice between loss of a 7r-electron from the C=0 double bond or one of the oxygen lone-pair electrons. Concordant data for the homologous series of aliphatic ketones have been obtained by... 

Mass spectrometric studies on iron(II) chloride and iron(II) bromide showed that monomers are the major species in the vapor phase, while concentration of the dimer, Fe2X4, increases with temperature in its certain interval. The electron diffraction data on iron(II) chloride could be well approximated by monomers only, while the data on the bromide indicated the presence of a detectable amount of dimeric species. This can be seen on the radial distribution of Fig. 12. It was found that there was about 10% dimeric qjecies present under the experimental conditions (nozzle temperature around 625 °C). As regards the relative scattering power, this constituted about 20%, and allowed only the determination of a limited amount of structural information. The electron diffraction date were consistent with a bridge stmcture characterized by the same Fe-Br, bond length as that of the monomeric... 

Since the aromaticity is defined as the stabilization due to cyclic electron (bond) delocalization, the data on thermodynamics and kinetics of various reactions leading to removal of cyclic delocalization system (or, conversely, to its formation) may in principle be used for assessing aromatic stabilization or antiaromatic destabilization. 

Wifckowski and coworkers [37] have reported adsorption of bisulfate anions on Au(lll), Pt(lll), and Rh(lll) electrodes in sulfuric acid solution using electrochemical and several nonelectrochemical techniques. It was concluded from the low-energy electron-diffraction data that the structure of bisulfate on gold is different from that on Pt(lll) and Rh(lll). Adsorption of bisulfate on Au(lll) is associated with a charge transfer from the electrode to the adsorbate. However, the formation of this particular bond does... 

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