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We propose a Cohen-type bond order analysis in terms of orthogonalized atomic basis functions which can be used to analyze NDO wave functions of large organic and metal–organic molecules. It is shown that for small molecules the results gained with this method are in excellent agreement with the same analysis based on ab initio STO -3G wavefunctions. For large planar aromatic systems these all-valence electron bond orders are found to be a consistent generalization of the π-bond order. A simple relation between these bond orders and the corresponding covalent bond energies is established. The method can be easily extended to study excited state multiconfiguration wave functions. We present calculations for C2H2, C2H4, C2H6, and Mn2(CO)10. The results indicate that the method can be used to discuss the photochemistry of organic and metal–organic compounds. 相似文献
13.
Molecular Composition of Liquid Sulfur. Part 2: Qualitative Analysis and Preparation of S7, S12, α-S18, and S20 from S8 Raman spectra of sulfur melts (115–300°C), of quenched melts and of CS2 extracts of quenched melts show besides S8 the presence of S6 and S7. Formation of S7 from S8 at 120°C takes more than 8 h; the S7 equilibrium concentration increases with temperature. Pure crystalline S7, S12, α-S18 and S20 are prepared on a preparative scale by fractional extraction, crystallization, flotation and precipitation of quenched sulfur melts. Also a mixture of larger rings (Sx; x? = 25) has been isolated. Infrared and Raman spectra of α-S18, S20 and Sx are reported. 相似文献
14.
Let A, B be two matrices of the same order. We write A>B(A>?B) iff A? B is a positive (semi-) definite hermitian matrix. In this paper the well-known result if (cf. Bellman [1, p.59]) is extended to the generalized inverses of certain types of pairs of singular matrices A,B?θ, where θ denotes the zero matrix of appropriate order. 相似文献
15.
Pfeifer P Aston L Banks M Barker S Burress J Carter S Coleman J Crockett S Faulhaber C Flavin J Gordon M Hardcastle L Kallenborn Z Kemiki M Lapilli C Pobst J Schott R Shah P Spellerberg S Suppes G Taylor D Tekeei A Wexler C Wood M Buckley P Breier T Downing J Eastman S Freeze P Graham S Grinter S Howard A Martinez J Radke D Vassalli T Ilavsky J 《Chaos (Woodbury, N.Y.)》2007,17(4):041108
16.
Michael Reinhardt Andreas Schnhals Dietmar Pfeifer Karl Pfeiffer Irene V. Lampe Hans-Joachim Lorkowski 《先进技术聚合物》1996,7(10):791-796
Dielectric relaxation spectroscopy in the frequency range from 10−2 Hz to 106 Hz and electron spin resonance (ESR) experiments are employed to study the dynamics in chemically and physically crosslinked networks. As examples for physically crosslinked networks ortho- and para-cresol novolacs were investigated. Dielectrically these materials show low-temperature β- and high-temperature α-relaxation. Both relaxation regions differ for both types of novolacs. This is also reflected by the ESR measurements and is discussed in terms of different hydrogen bonds found to be stronger in para-cresol novolac. For the chemically crosslinked poly(triallyl isocyanurate) only a β-peak is found by the dielectric measurements. Also in the ESR experiment the slow motion regime is characterized up to high temperatures. This means that the segmental motion is strongly suppressed by chemical crosslinking. Nevertheless the obtained change in the formal T50G value can be used to characterize the glass transition in highly crosslinked systems by the ESR method. 相似文献
17.
Hans-Joachim Nees Uwe Bergstrßer Heinrich Heydt Manfred Regitz 《Heteroatom Chemistry》1993,4(5):525-530
The (diazoalkyl)phosphanes 4a–e undergo [4 + 1]-cycloaddition reactions with the tetrahalo-orthobenzoquinones 5a,b to furnish the previously unknown (diazoalkyl)phosphoranes 6a–h . The structure of product 6h has been investigated by X-ray crystallography. 相似文献
18.
Hans-Joachim Bhm 《Nachrichten aus der Chemie》1993,41(6):711-712
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