Search results for "Configuration"
showing 10 items of 601 documents
Perturbative treatment of triple excitations in coupled‐cluster calculations of nuclear magnetic shielding constants
1996
A theory for the calculation of nuclear magnetic shielding constants at the coupled‐cluster singles and doubles level augmented by a perturbative correction for connected triple excitations (CCSD(T)) has been developed and implemented. The approach, which is based on the gauge‐including atomic orbital (GIAO) ansatz, is illustrated by several numerical examples. These include a comparison of CCSD(T) and other highly correlated methods with full configuration interaction for the BH molecule, and a systematic comparison with experiment for HF, H2O,NH3, CH4, N2, CO, HCN, and F2. The results demonstrate the importance of triple excitations in establishing quantitative accuracy. Finally, the abil…
Acid-induced rearrangement of epoxygermacra-8,12-olides: synthesis and absolute configuration of guaiane and eudesmane derivatives from artemisiifolin
2010
A study on the acid-induced rearrangement of 4,5-epoxy- and 1,10-epoxygermacra-8,12-olides was carried out. From a 4,5-epoxy derivative, guaianes were obtained, whereas 1,10-epoxy derivatives furnished, depending on the stereochemistry of the C-1/C-10 epoxy ring, trans-5β,10α- or trans-5α,10β-eudesmanolides.
Synthesis of 8-aminomorphans with high KOR affinity
2021
2-Azabicyclo[3.3.1]nonanes (morphans) with a (3,4-dichlorophenyl)acetyl group at 2-position and a pyrrolidino moiety at 8-position were designed as conformationally restricted analogs of piperidine-based KOR agonists. The synthesis started with 4-oxopiperidine-2-carboxylic acid comprising 13 reaction steps. At first the ketone 10 was transformed into diester 7 bearing a propionate side chain. Dieckmann condensation of diester 7 to afford bicyclic enolester 14 and subsequent Krapcho deethoxycarbonylation represent the key steps of the synthesis. The enantiomeric pyrrolidines (1S,5R,8R)-5a and (1R,5S,8S)-5a were separated by chiral HPLC. The eutomer (1S,5R,8R)-5a showed high KOR affinity (K-i…
Selected dissociation‐ and correlation‐consistent configuration interaction by a perturbative criterion
1990
We propose a perturbative criterion to select the most important dissociation‐ or correlation‐consistent type of contributions to perform generalized valence bond‐configuration interaction (GVB‐CI) calculations, dissociation‐consistent configuration interaction (DCCI) or correlation‐consistent configuration interaction (CCCI) approach, respectively. The procedure presented is computationally less demanding than the CCCI proposed by Goddard and co‐workers. To ensure the distance consistency of the MOs used, the nonvalence virtual orbitals are obtained by a projection technique. The results obtained for a few test calculations show the ability of the suggested approach to get close results to…
Stereoselective Synthesis of Chiral Piperidine Derivatives Employing Arabinopyranosylamine as the Carbohydrate Auxiliary.
2006
Stereoselective synthesis of 2-substituted dehydropiperidinones and their further transformation to variously disubstituted piperidine derivatives was achieved employing D-arabinopyranosylamine as the stereodifferentiating carbohydrate auxiliary. A domino MannichMichael reaction of 1-methoxy-3-(trimethylsiloxy)butadiene (Danishefsky's diene) with O-pivaloylated arbinosylaldimines furnished N-arabinosyl dehydropiperidinones in high diastereoselectivity. Subsequent conjugate cuprate addition gave 2,6-cis-substituted piperidinones, while enolate alkylation furnished 2,3-trans-substituted dehydropiperidinones. Electrophilic substitution at the enamine structure afforded 5-nitro- and 5-halogen…
Structural characterization of carane derivative stereoisomers - Potent local anesthetics
2002
The paper reports on structural investigation and phase analysis of a newly synthesized potent local anesthetic with chiral molecular structure. Absolute structure and absolute configuration on four chiral centres was determined using microcrystalline single-crystal difracti on with anomalous scattering of X-ray radiation azimuthal scan technique. Phase analysis for new compound (K P23SS) and its epimer (K P23 RS) was carried out using classical and synchrotron radiation powder difraction. Enantiopurity of the bulk material was verifed for both isomers by comparison of experimental and simulated high- resolution powder difraction diagrams. The presence of two new polymorphic phases of K P23…
Magic numbers, excitation levels, and other properties of small neutral math clusters (N < 50)
2006
The ground-state energies and the radial and pair distribution functions of neutral math clusters are systematically calculated by the diffusion Monte Carlo method in steps of one math atom from 3 to 50 atoms. In addition the chemical potential and the low-lying excitation levels of each cluster are determined with high precision. These calculations reveal that the “magic numbers” observed in experimental math cluster size distributions, measured for free jet gas expansions by nondestructive matter-wave diffraction, are not caused by enhanced stabilities. Instead they are explained in terms of an enhanced growth due to sharp peaks in the equilibrium concentrations in the early part of the e…
The UN in the Lab
2013
We consider two alternatives to inaction for governments combating terrorism, which we term Deterrence and Prevention. Deterrence – investing in resources that reduce the impact of an attack – generates a negative externality to other governments, making their countries a more attractive objective for terrorists, while Prevention – investing in resources that reduce the ability of the terrorist organization to mount an attack – creates a positive externality by reducing the overall threat of terrorism for all. Due to the structure of this interaction, countries can benefit from coordination of policy choices, and international institutions (such as the UN) can be utilized to facilitate coor…
The new 5- or 6-azapyrimidine and cyanuric acid derivatives of L-ascorbic acid bearing the free C-5 hydroxy or C-4 amino group at the ethylenic space…
2011
Abstract We report on the synthesis of the novel types of cytosine and 5-azacytosine (1–9), uracil and 6-azauracil (13–18) and cyanuric acid (19–22) derivatives of l -ascorbic acid, and on their cytostatic activity evaluation in human malignant tumour cell lines vs. their cytotoxic effects on human normal fibroblasts (WI38). The CD spectra analysis revealed that cytosine (5 and 6), uracil (14–16), 6-azauracil (17) and cyanuric acid (21) derivatives of l -ascorbic acid bearing free amino group at ethylenic spacer existed as a racemic mixture of enantiomers, whereas L-ascorbic derivatives containing the C-5 substituted hydroxy group at the ethylenic spacer were obtained in (4R, 5S) enantiomer…
A novel methodology for accelerating bitstream relocation in partially reconfigurable systems
2012
International audience; Xilinx Virtex FPGAs offer the possibility of Partial Reconfiguration (PR). Arbitrary tasks can be allocated and de-allocated onto FPGA without system interruption. However, mapping a task to any available PR region requires a unique partial bitstream for each partition, hence reducing memory storage requirements. In recent years, an interest on overcoming this problem has lead to the concept of Partial Bitstream Relocation (PBR). The principle is to perform bitstream modification to map it to different regions. However, PBR consumes scarce resources in hardware implementations, and introduces a prohibitive time overhead when done in software. In order to find the bes…