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31.
R. W. Warren D. S. Gates G. L. Driscoll 《Journal of polymer science. Part A, Polymer chemistry》1971,9(3):717-746
The composition of nonvolatile fluids obtained from thermally cracking and hydrogenating polyisobutylene was determined by using a combination of gas chromatography and nuclear magnetic resonance spectroscopy (NMR). This work involved the separation and characterization of a homologous series, C11–C40, of sixteen branched hydrocarbon species consisting of repeating isobutylene structures. As a result of this investigation, useful correlations between NMR spectra and molecular structure for highly branched hydrocarbons were developed. The data demonstrate that these hydrocarbons are unique species characterized by “crowded” and sterically hindered geminal methyl and isolated methylene groups. NMR solvent shift studies in benzene solutions indicate that it is possible to differentiate between maximally crowded geminal methyl groups and between maximally crowded methylene groups in these structures. Results of the benzene-induced solvent effects are discussed with respect to the stereochemistry of these molecules and related to existing solvent shift data. These results suggest that these hydrocarbons are polar or nearly polar materials. Successive losses of isobutylene units from stabilized tertiary radicals can account for the formation of the major species identified in these fluids. Higher carbon numbered species have lower refractive indices and densities and higher molal volumes than predicted by calculations. 相似文献
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Sarkar U Glaser R Parsons ZD Barnes CL Gates KS 《Journal of chemical crystallography》2010,40(7):624-629
Abstract
1,2,4-Benzotriazine 1,4-di-N-oxides are potent antitumor drug candidates that undergo in vivo bioreduction leading to selective DNA damage in the low oxygen (hypoxic) cells found in tumors. Tirapazamine (TPZ) is the lead compound in this family. Here we report on the synthesis, crystal structure, and conformational analysis of a new analog, 3-cyclopropyl-1,2,4-benzotriazine 1,4-di-N-oxide (3). Compound 3 (C10H10N3O2) crystallized in the monoclinic space group C2/c. Unit cell parameters for 3: a = 16.6306 (12), b = 7.799 (5), c = 16.0113 (11) ?, α = 90, β = 119.0440 (10), γ = 90, and z = 8. 相似文献38.
Henry T. G. Walsgrove Khadiza K. Chowdhury Philipp Dabringhaus Dr. Brian O. Patrick Prof. Dr. Derek P. Gates 《欧洲无机化学杂志》2023,26(20):e202300182
The anionic polymerization of 1-phosphaisoprene [Mes*P=C(Me)−CH=CH2 (E- 1 )] affords poly(1-phosphaisoprene) 2 in high yield (75 %). Concentrated solutions of polymer 2 (Mn=21,800 g mol−1; Đ=1.02) a P-analogue of natural rubber, undergo gelation upon treatment with [Pd(cod)Cl2] (0.15 P equiv). Evidence for P-coordination of 2 to PdII was obtained by 31P and 1H NMR spectroscopy. The gelation is reversed by the addition of PMe3 and the reformation of recoverable 2 along with [PdII−PMe3] complexes were confirmed by 31P NMR spectroscopy. The use of labile metal-ligand bonds to reversibly form gels is unprecedented and has relevance to self-healing materials. In contrast, coordination of 2 to [Pd(η3-C3H5)(μ-Cl)]2 affords the well-defined complex 2 ⋅ [Pd(η3-C3H5)Cl] which was characterized by 31P, 1H, 13C{1H} NMR spectroscopy and GPC. This polymer chemistry was complemented by detailed molecular model studies of the coordination chemistry of monomer 1-phosphaisoprene E- 1 with [Pd(cod)Cl2] and [Pd(η3-C3H5)(μ-Cl)]2]. 相似文献
39.
H. Henry Lamb Bruce C. Gates Helmut Knzinger 《Angewandte Chemie (International ed. in English)》1988,27(9):1127-1144
Metal carbonyls react on metal oxide surfaces to give a wide range of structures analogous to those of known compounds. The reactions leading to formation of surface-bound metal carbonyls are explained by known molecular organometallic chemistry and the functional group chemistry of the surfaces. The reaction classes include formation of acid-base adducts as the oxygen of a carbonyl group donates an electron pair to a Lewis acidic center; nucleophilic attack at CO ligands by basic surface hydroxyl groups or O2? ions; ion-pair formation by deprotonation of hydrido carbonyls to give carbonylate ions; interaction of bifunctional complexes with surface acid-base pair sites such as [Mg2⊕O2?]; and oxidative addition of surface hydroxyl groups to metal clusters. The reactions of surface-bound organometallic species include redox condensation and cluster formation on basic surfaces (paralleling the reactions in basic solution) as well as oxidation of mononuclear metal complexes and oxidative fragmentation of metal clusters by reaction with surface hydroxyl groups. Most supported metal carbonyls are unstable at high temperatures, but some, including osmium carbonyl cluster anions on the basic MgO surface, are strongly stabilized in the presence of CO and are precursors of catalysts for CO hydrogenation at 550 K. 相似文献
40.
Fierro-Gonzalez JC Kuba S Hao Y Gates BC 《The journal of physical chemistry. B》2006,110(27):13326-13351
This article is a review of the physical characterization of well-defined site-isolated molecular metal complexes and metal clusters supported on metal oxides and zeolites. These surface species are of interest primarily as catalysts; as a consequence of their relatively uniform structures, they can be characterized much more precisely than traditional supported catalysts. The properties discussed in this review include metal nuclearity, oxidation state, and ligand environment, as well as metal-support interactions. These properties are determined by complementary techniques, including transmission electron microscopy; X-ray absorption, infrared, Raman, and NMR spectroscopies; and density functional theory. The strengths and limitations of these techniques are assessed in the context of results characterizing samples that have been investigated thoroughly and with multiple techniques. The depth of understanding of well-defined metal complexes and metal clusters on supports is approaching that attainable for molecular analogues in solution. The results provide a foundation for understanding the more complex materials that are typical of industrial catalysts. 相似文献