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71.
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73.
Broadband irradiation (lambda > 320 nm) of hemicarceplex H(.)1 between -74 degrees C and -84 degrees C, produces encapsulated didehydroazepine (2), triplet phenylnitrene ((3)PN), 2-azabicyclo[3.2.0]hepta-1,3,6-triene (6), and 4-azaspiro[2.4]hepta-1,4,6-triene (7). The highly strained anti-Bredt imine 6 is formed from 2 via a photochemical four-electron electrocyclization. Under the irradiation conditions, 6 rearranges further to azaspirene 7. In addition, 6 thermally rearranges to 7 via a 1,5-sigmatropic shift (DeltaG(267K) = 20.0 +/- 0.5 kcal/mol), yielding a final equilibrium composed of [7]/[6] = 5 at room temperature. The observation of a photochemical rearrangement of 2 to 6 contrasts earlier results of narrow band irradiations (lambda = 334 nm) of matrix-isolated 2, which gave (3)PN (Hayes, J. C.; Sheridan, R. S. J. Am. Chem. Soc. 1990, 112, 5879-5881). Encapsulated (3)PN is remarkably stable due to the prevention of its dimerization by the surrounding hemicarcerand. Above 255 K, it slowly decays with a rate constant k = 10(7.7+/-0.4) s(-1) x exp {(13300 +/- 500 cal/mol)/RT}. The isolation of substantial amounts of a hemicarcerand lacking one acetal spanner suggests that (3)PN decays preferentially by inserting into an inward-pointing acetal C-H bond of H. 相似文献
74.
You X Wang H Goos E Sung CJ Klippenstein SJ 《The journal of physical chemistry. A》2007,111(19):4031-4042
The kinetics of the reaction CO + HO2* --> CO2 + *OH was studied using a combination of ab initio electronic structure theory, transition state theory, and master equation modeling. The potential energy surface was examined with the CCSD(T) and CASPT2 methods. The classical energy barriers were found to be about 18 and 19 kcal/mol for CO + HO2* addition following the trans and cis paths, respectively. For the cis path, rate constant calculations were carried out with canonical transition state theory. For the trans path, master equation modeling was also employed to examine the pressure dependence. Special attention was paid to the hindered internal rotations of the HOOC*O adduct and transition states. The theoretical analysis shows that the overall rate coefficient is independent of pressure up to 500 atm for temperature ranging from 300 to 2500 K. On the basis of this analysis, we recommend the following rate expression for reaction R1 k(cm(3)/mol x s) = 1.57 x 10(5) T(2.18)e(-9030/T) for 300 < or = T < or = 2500 K with the uncertainty factor equal to 8, 2, and 1.7 at temperatures of 300, 1000, and 2000 K, respectively. 相似文献
75.
Molecular container compounds have a range of potential applications in chemical and biological sciences, most notably as nanoreactors, drug delivery devices, and storage materials. We report a highly efficient dynamic covalent chemistry approach for the synthesis of covalent rhombicuboctahedral nanocapsule 1 from 14 square- and triangular-shaped molecular components. The nanocapsule is obtained in a one-pot reaction in high yield and high purity, and has a solvodynamic diameter of 3.9 nm. In our approach, six formyl cavitands and eight 1,3,5-tris(p-aminophenyl)benzene molecules are assembled into a molecular rhombicuboctahedron through twenty four newly formed dynamic imine bonds. Binding studies show that 1 encapsulates tetraalkylammonium salts in toluene. We also discuss the growth mechanism of this nanocapsule. 相似文献
76.
77.
78.
Reactions of Uranium Pentabromide. Crystal Structures of PPh4[UBr6], PPh4[UBr6] · 2CCl4, (PPh4)2[UBr6] · 4CH3CN, and (PPh4)2[UO2Br4] · 2CH2Cl2 PPh4[UBr6] and PPh4[UBr6] · 2CCl4 were obtained from UBr5 · CH3CN and tetraphenylphosphonium bromide in dichloromethane, the latter being precipitated by CCl4. Their crystal structures were determined by X-ray diffraction. PPh4[UBr6]: 2101 observed reflexions, R = 0.090, space group C2/c, Z = 4, a = 2315.5, b = 695.0, c = 1805.2 pm, β = 96.38°. PPh4[UBr6] · 2CCl4: 2973 reflexions, R = 0.074, space group P21/c, Z = 4, a = 1111.5, b = 2114.2, c = 1718.7 pm, β = 95.42°. Hydrogen sulfide reduces uranium pentabromide to uranium tetrabromide. Upon evaporation, bromide is evolved from solutions of UBr5 with 1 or more then 3 mol equivalents of acetonitrile in dichlormethane yielding UBr4 · CH3CN and UBr4 · 3CH3CN, respectively. These react with PPh4Br in acetonitrile affording (PPh4)2[UBr6] · 4CH3CN, the crystal structure of which was determined: 2663 reflexions, R = 0.050, space group P21/c, Z = 2, a = 981.8, b = 2010.1, c = 1549.3 pm, β = 98.79°. By reduction of uranium pentabromide with tetraethylammonium hydrogen sulfide in dichloromethane (NEt4)2[U2Br10] was obtained; (PPh4)2[U2Br10] formed from UBr4 and PPh4Br in CH2Cl2. Both compounds are extremely sensitive towards moisture and oxygen. The crystal structure of the oxydation product of the latter compound, (PPh4)2[U02Br4]· 2 CH2Cl2, was determined: 2163 reflexions, R = 0.083, space group C2/c, Z = 4, a = 2006.3, b = 1320.6, c = 2042,5 pm, β = 98.78°. Mean values for the UBr bond lengths in the octahedral anions are 266.2 pm for UBr6-, 276.7 pm for UBr62? and 282.5 pm for UO2Br42? 相似文献
79.
Batrice Alpha Elke Anklam Robert Deschenaux Jean-Marie Lehn Marek Pietraskiewiez 《Helvetica chimica acta》1988,71(5):1042-1052
Sythetic procedures have been deweloped for the preparation of sodium and lithium cryptates of the macrabicyclic ligands 1–11 containing pyridine, bipyridine, and biisoquinoline groups. They involve stepwise construction of the bicyclic system as will as direct macrobicyclisation procedures (Scheme 1) and give access to both symmetrical and dissymmetrical structures. Marked cation template effects have been found that facilitate the cyclisation processes. The ligands 1–11 were isolated as their cryptates with Na+ or Li+ cations. 相似文献
80.
Manfredo Hrner Vanessa S. Carratu Jairo Bordinhao Angela Silva Elke Niquet 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(3):m140-m142
In the title compound, [Cd(C12H8F2N3)2(C5H5N)2], the Cd atom lies on a crystallographic twofold axis in space group Iba2. The coordination geometry about the CdII ion corresponds to a rhombically distorted octahedron, with two deprotonated 1,3‐bis(2‐fluorophenyl)triazenide ions, viz. FC6H4NNNC6H4F−, acting as bidentate ligands (four‐electron donors). Two neutral pyridine (py) molecules complete the coordination sphere in positions cis with respect to one another. The triazenide ligand is not planar (r.m.s. deviation = 0.204 Å), the dihedral angle between the phenyl rings of the terminal 2‐fluorophenyl substituents being 24.6 (1)°. The triazenide and pyridine Cd—N distances are 2.3757 (18)/2.3800 (19) and 2.3461 (19) Å, respectively. Intermolecular C—H⋯F interactions generate sheets of molecules in the (010) plane. 相似文献