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231.
Brain PT Cowie J Donohoe DJ Hnyk D Rankin DW Reed D Reid BD Robertson HE Welch AJ Hofmann M Schleyer PR 《Inorganic chemistry》1996,35(6):1701-1708
The compound 1-phenyl-1,2-dicarba-closo-dodecaborane(12), 1-C(6)H(5)-1,2-closo-C(2)B(10)H(11) (1), has been synthesized and characterized by a complete assignment of its (11)B NMR spectrum via (11)B{(1)H}/(11)B{(1)H} (COSY), (1)H{(11)B(selective)} and (1)H{(11)B}/(1)H{(11)B} (COSY) spectroscopy. An electron- and X-ray diffraction investigation of 1, complemented by ab initio calculations, has been undertaken. The gas-phase electron-diffraction (GED) data can be fitted by several models describing conformations which differ in the position of the phenyl ring with respect to the carborane cage. Local symmetries ofC(2)(v)() and D(6)(h)() for the 1,2-C(2)B(10) and C(6) moieties, respectively, were adopted in the GED model in order to simplify the problem. In addition, constraints among the close-lying C-C and B-B bonds were employed. However, even though such simplifications led to satisfactory refinements (R(G) = 0.069-0.071), a unique, definitive solution could not be gained. The (C-C)(mean), (C-B)(mean) and (B-B)(mean) bond lengths,r(a), are ca. 1.44, 1.72, and 1.78 ?, respectively. The C(6) hexagon, with r(a)(C-C) = ca. 1.394 ?, either eclipses the C(1)-C(2) vector (overall C(s)() symmetry) or more or less eclipses the C(1)-B(4) cluster bond (overall C(1) symmetry). In contrast, in the solid at 199 K, the ring lies at a position intermediate between the two GED positions, as determined by X-ray crystallography [C(8)H(16)B(10), monoclinic P2(1)/a: a = 12.047(3) ?, b = 18.627(4) ?, c = 12.332(5) ?, beta = 110.09(4) degrees, Z = 8]. The C-B distances span the range 1.681(6)-1.743(5) ?, and B-B lengths lie between 1.756(6) and 1.795(6) ?. A similar conformation was found for the theoretical (RHF/6-31G level) structure which was fully optimized in C(1) symmetry. The r(e) distances are consistent with the dimensions derived in the experimental studies. IGLO calculations of the (11)B chemical shifts, in addition to SCF single-point energies of the GED structures, further support these observations. 相似文献
232.
233.
W. E. Collins A. H. Welch J. H. Hamilton A. V. Ramayya N. C. Singhal 《Zeitschrift für Physik A Hadrons and Nuclei》1978,285(1):31-32
The gamma-gamma directional correlation of the 2+′-2+-0+, 913(Iγ=1.69)-934(Iγ =100)keV cascade in92Nb decay has been investigated with a NaI-Ge(Li) system. Our results yieldδ=?0.013 ?0.024 +0.041 . This is one of a very few cases where the second 2+ to first 2+ transition is not predominatelyE2. This may be related to the closed neutron shell, as earlier suggested. [Radioactivity92Zr; measuredγ-γ(θ), deducedδ] 相似文献
234.
14‐Vertex Heteroboranes with 14 Skeletal Electron Pairs: An Experimental and Computational Study 下载免费PDF全文
Dr. Alasdair P. M. Robertson Nicholas A. Beattie Dr. Greig Scott Dr. Wing Y. Man John J. Jones Prof. Stuart A. Macgregor Dr. Georgina M. Rosair Prof. Alan J. Welch 《Angewandte Chemie (International ed. in English)》2016,55(30):8706-8710
Three isomers of [(Cp*Ru)2C2B10H12], the first examples of 14‐vertex heteroboranes containing 14‐skeletal electron pairs, have been synthesized by the direct electrophilic insertion of a {Cp*Ru+} fragment into the anion [4‐Cp*‐4,1,6‐RuC2B10H12]?. All three compounds have the same unique polyhedral structure having an approximate Cs symmetry and featuring a four‐atom trapezoidal face. X‐ray diffraction studies could confidently identify only one of the two cage C atoms in each structure. The other C atom position has been established by a combination of i) best fitting of computed and experimental 11B and 1H NMR chemical shifts, and ii) consideration of the lowest computed energy for series of isomers studied by DFT calculations. In all three isomers, one cage C atom occupies a degree‐4 vertex on the short parallel edge of the trapezium. 相似文献
235.
Multiple‐injection techniques have been shown to be a simple way to perform high‐throughput analysis where the entire experiment resides in a single chromatogram, simplifying the data analysis and interpretation. In this study, multiple‐injection techniques are applied to gas chromatography with flame ionization detection and mass detection to significantly increase sample throughput. The unique issues of implementing a traditional “Fast” injection mode of multiple‐injection techniques with gas chromatography and mass spectrometry are discussed. Stacked injections are also discussed as means to increase the throughput of longer methods where mass detection is unable to distinguish between analytes of the same mass and longer retentions are required to resolve components of interest. Multiple‐injection techniques are shown to increase instrument throughput by up to 70% and to simplify data analysis, allowing hits in multiple parallel experiments to be identified easily. 相似文献
236.
Hutton BW MacIntosh F Ellis D Herisse F Macgregor SA McKay D Petrie-Armstrong V Rosair GM Perekalin DS Tricas H Welch AJ 《Chemical communications (Cambridge, England)》2008,(42):5345-5347
The reduction and subsequent oxidation of meta-carboranes containing bulky groups attached to the cage C atoms affords sterically-crowded ortho-carboranes with unprecedentedly long C-C connectivities. 相似文献
237.
238.
In this paper we first give a variant of a theorem of Jockusch–Lewis– Remmel on existence of a computable, degree-preserving homeomorphism between a bounded strong ${\Pi^0_2}$ class and a bounded ${\Pi^0_1}$ class in 2 ω . Namely, we show that for mathematically common and interesting topological spaces, such as computably presented ${\mathbb{R}^n}$ , we can obtain a similar result where the homeomorphism is in fact the identity mapping. Second, we apply this finding to give a new, priority-free proof of existence of a tree of shadow points computable in 0′. 相似文献
239.
Michael A. Duncan David Welch Igor Shuryak David J. Brenner 《Photochemistry and photobiology》2023,99(1):160-167
Far-UVC radiation, defined in this paper as ultraviolet (UV) radiation with wavelengths from 200 to 235 nm, is a promising tool to help prevent the spread of disease. The unique advantage of far-UVC technology over traditional UV germicidal irradiation lies in the potential for direct application of far-UVC into occupied spaces since antimicrobial doses of far-UVC are significantly below the recommended daily safe exposure limits. This study used a ceiling-mounted far-UVC fixture emitting at 222 nm to directly irradiate an indoor space and then evaluated the doses received upon a manikin. Radiation-sensitive film was affixed to the head, nose, lip and eyes of the manikin, and the 8-h equivalent exposure dose was determined. Variables examined included manikin height (sitting or standing position), manikin offset from directly below the fixture, tilt of the manikin, the addition of glasses, the addition of hair and different anatomical feature sizes. Importantly, at the manikin position with the highest dose to eyes, the average eye dose was only 5.8% of the maximum directly measured dose. These results provide the first experimental analysis of possible exposure doses a human would experience from an indoor far-UVC installation. 相似文献
240.
A solution of SF5Br in CCl3F (0.5-1 M) was utilized to effect the addition of pentafluorosulfanyl bromide (SF5Br) to olefins. The reaction of the SF5Br solution in the presence of triethylborane (0.1 equiv) with an olefin over 20 min at 0 °C gave pentafluorosulfanylated compound 2(a-f) in high yield (Table 2). An efficient route for the preparation of synthetically useful SF5-containing esters is also described. 相似文献