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991.
Sheng‐Li Huang Yue‐Jian Lin Zhen‐Hua Li Prof. Guo‐Xin Jin 《Angewandte Chemie (International ed. in English)》2014,53(42):11218-11222
In contrast to conventional stepwise synthesis of molecular Borromean rings, a self‐assembly synthetic method which proceeds without the aid of a template has been developed. In the formation of molecular rectangles, by adjustment of the long‐arm length of the rectangles, a series of size‐dependent Borromean‐link frameworks were constructed. Both the shortest length of two arms and the relative proportion of the length of the long arm to that of the short arm play a key role in the formation of Borromean rings. DFT calculations were used to provide theoretical support for the formation of discrete interlocked frameworks. 相似文献
992.
The objective of this article is to establish a fixed point theorem using different class of control functions, which is a generalization of Darbo’s fixed point theorem (DFPT) and its various versions obtained by several authors. Using this result we obtain existence of at least one positive solution for a quadratic integral equation of Fredholm type. 相似文献
993.
A three-dimensional complex [Cu(3-ampy)(H2O)4](SO4)·(H2O) (3-ampy = 3-aminopyridine) has been synthesized. Crystallographic data: C5H16CuN2O9S, Mr = 343.80, triclinic, space group P, a = 7.675(2), b = 8.225(3), c = 10.845(3) (A), α= 86.996(4), β = 76.292(4),γ = 68.890(4)°, V = 620.0(3) (A)3, Z = 2, Dc = 1.841 g/cm3, F(000) = 354 and μ = 1.971 mm-1. The structure was refined to R = 0.0269 and wR = 0.0659 for 1838 observed reflections (I > 2σ(Ⅰ)). The structure consists of [Cu(3-ampy)(H2O)4]2 cations, SO42- anions and lattice water molecules. 3-Ampy acting as a bidentate bridging ligand generates a 1D covalent chain. A supramolecular 2D framework is formed through π-π stacking of pyridine rings. The lattice water molecules and SO42- anions are located between the adjacent 2D frameworks. The hydrogen bonding interactions from lattice water molecules and SO42- anions to coordinate water extend the 2D framework into a 3D network. 相似文献
994.
Large amplitude motions (LAMs) form a fundamental phenomenon that demands the development of specific theoretical and Hamiltonian models. In recent years, along with the strong progress in instrumental techniques on high-resolution microwave spectroscopy and computational capacity in quantum chemistry, studies on LAMs have become very diverse. Larger and more complex molecular systems have been taken under investigation, ranging from series of heteroaromatic molecules from five- and six-membered rings to polycyclic-aromatic-hydrocarbon derivatives. Such systems are ideally suited to create families of molecules in which the positions and the number of LAMs can be varied, while the heteroatoms often provide a sufficient dipole moment to the systems to warrant the observation of their rotational spectra. This review will summarize three types of LAMs: internal rotation, inversion tunneling, and ring puckering, which are frequently observed in aromatic five-membered rings such as furan, thiophene, pyrrole, thiazole, and oxazole derivatives, in aromatic six-membered rings such as benzene, pyridine, and pyrimidine derivatives, and larger combined rings such as naphthalene, indole, and indan derivatives. For each molecular class, we will present the representatives and summarize the recent insights on the molecular structure and internal dynamics and how they help to advance the field of quantum mechanics. 相似文献
995.
Tomoki Furukawa Tomoyuki Yanagi Atsushi Kaga Hayate Saito Hideki Yorimitsu 《Helvetica chimica acta》2021,104(12):e2100195
Treatment of a mixture of dibenzothiophene dioxides and benzaldehyde N-benzylimines with potassium hexamethyldisilazide induces sequential intermolecular and intramolecular SNAr reactions to eventually form the corresponding 5H-dibenzo[c,e]azepines without any formation of the conceivable five-membered fluorene derivatives. 相似文献
996.
997.
Highly Efficient Enrichment of Volatile Iodine by Charged Porous Aromatic Frameworks with Three Sorption Sites 下载免费PDF全文
Dr. Zhuojun Yan Dr. Ye Yuan Dr. Yuyang Tian Prof. Daming Zhang Prof. Guangshan Zhu 《Angewandte Chemie (International ed. in English)》2015,54(43):12733-12737
The targeted synthesis of a series of novel charged porous aromatic frameworks (PAFs) is reported. The compounds PAF‐23, PAF‐24, and PAF‐25 are built up by a tetrahedral building unit, lithium tetrakis(4‐iodophenyl)borate (LTIPB), and different alkyne monomers as linkers by a Sonogashira–Hagihara coupling reaction. They possess excellent adsorption properties to organic molecules owing to their “breathing” dynamic frameworks. As these PAF materials assemble three effective sorption sites, namely the ion bond, phenyl ring, and triple bond together, they exhibit high affinity and capacity for iodine molecules. To the best of our knowledge, these PAF materials give the highest adsorption values among all porous materials (zeolites, metal–organic frameworks, and porous organic frameworks) reported to date. 相似文献
998.
Iyoda M Yamakawa J Rahman MJ 《Angewandte Chemie (International ed. in English)》2011,50(45):10522-10553
One of the most important objectives in materials, chemical, and physical sciences is the creation of large conjugated macrocycles with well-defined shapes, since such molecules are not only theoretically and experimentally interesting but also have potential applications in nanotechnology. Fully unsaturated macrocycles are regarded as models for infinitely conjugated π systems with inner cavities, and exhibit unusual optical and magnetic behavior. Macrocycles have interior and exterior sites, and site-specific substitution at both or either site can afford attractive structures, such as 1D, 2D, and 3D supramolecular nanostructures. These nanostructures could be controlled through the use of π-extended large macrocycles by a bottom-up strategy. Numerous shape-persistent π-conjugated macrocycles have been synthesized, but only a few are on the nanoscale. This Review focuses on nanosized π-conjugated macrocycles (>1 nm diameter) and giant macrocycles (>2 nm diameter), and summarizes their syntheses and properties. 相似文献
999.
Aav R Pehk T Tamp S Tamm T Kudrjašova M Parve O Lopp M 《Magnetic resonance in chemistry : MRC》2011,49(2):76-82
Spin-spin coupling constants between nuclei in NMR spectroscopy reflect their spatial arrangement. A number of calculation methods, applying different levels of theory, have been developed to support the stereochemical assignment of novel compounds. Nevertheless, revisions of the assignment of structures in the literature are not rare. In the present work, the reliability of the calculation methods amenable for a theoretical prediction of spin-spin coupling constants of vicinal protons to support correct stereochemical assignment of substitution at five-membered rings of 3-alkoxy-6,7-epoxy-2-oxabicyclo[3.3.0]octanes was studied. Experimental (3)J(H,H) coupling constants were compared with the coupling constants calculated for all possible diastereomers. The fully quantum chemical approach provided theoretical (3)J(H,H) coupling constants with an absolute deviation of no more than 1.1 Hz for 91% of the experimentally studied coupled spins, whereas the methods without quantum chemical geometry optimization resulted in completely unreliable predictions. Consequently, for a reliable stereochemical assignment of small and medium size molecules, the protocol for calculating the coupling constants based on the results of the quantum chemical geometry optimization is recommended. 相似文献
1000.
Three new bis-triazolinediones, 3,3′-dimethyl-4,4′-bis-[3,5-dioxo-1,2,4-triazoline-4-yl]biphenyl, t-1,4-bis-[3,5-dioxo-1,2,4-triazoline-4-yl]methyl cyclohexane, and 4,4′-bis-[3,5-dioxo-1,2,4-triazoline-4-yl] phenyl ether, were synthesized from their corresponding bis-amines or bis-isocyanates. The compounds were identified by their quantitative ene reaction with 2,3-dimethyl-2-butene. The high degree of reactivity of the triazoline moiety makes solvent selection for reaction media rather difficult. This fact prompted a study of rates of reaction with a variety of polar and nonpolar solvents, including halogenated aliphatics, aromatics, tetrahydrofuran (THF), and N,N-dimethylformamide (DMF). The compounds exhibited reasonable stability in the halogenated solvents, as well as in the aliphatic and aromatic hydrocarbons, but they underwent reaction with THF and DMF. The structure of the reaction product of N-phenyl-1,2,4-triazoline-3,5-dione in DMF solution was determined, and a mechanism for product formation was proposed. Two of the bis- triazolinediones were polymerized via a base-catalyzed condensation mechanism which eliminates N2 from the triazolinedione ring. 相似文献