Search results for "bond"
showing 10 items of 3527 documents
COMMUNICATION. OBSERVATIONS ON THE 121-Sb MÖSSBAUER PARAMETERS OF ANTIMONY (III) COMPOUNDS FEATURING A PYRAMIDAL SbS3SKELETAL UNIT
1991
Abstract A linear correlation between the chemical isomer shift and the quadrupole coupling constant for a number of antimony tris-thiolates has been evidenced. This behaviour can be rationalized on considering a modulation of the s/p character of the lone pair of electrons from the influence of secondary bonds.
Mössbauer spectroscopic studies of clusters Mn2(CO)8[μ-Sn(hal)Mn(CO)5]2 (hal = Cl, Br) and related Mn and Re compounds
1977
Abstract In order to be acquainted with the nature of bonds at Sn involved in the title compounds, as well as to get information on the configuration of the strictly related derivatives I2Sn2Mn4(CO)18 and Cl2Sn2Re4(CO)18, the Mossbauer spectroscopic investigation reported in this paper has been carried out. The experimental parameters (isomer shifts, δ; nuclear quadrupole splittings, ΔE; for the bromide derivative only, the asymmetry parameter η and the sign of the nuclear quadrupole coupling constant e2qQ) have been discussed in connection with data concerning compounds with tin-transition metal bonds, mainly hal2Sn[Mn(CO)5]2 (hal = Cl, Br) and ClSn[Mn(CO)5]3. Rationalizations of ΔE and η …
Nonbonded Indirect Nuclear Spin–Spin Couplings (J Couplings “Through-Space”) for Structural Determination in Small Organic and Organometallic Species
2013
Abstract Spin–spin coupling constant J provides decisive data for organic compound characterization. This electron-mediated coupling is usually taught as transmitted between covalently bonded magnetic atoms. However, this physical interaction between nuclear spins is much more complex than that with regard to chemical bonding concept. Independent experimental and theoretical studies related to small organic and organometallic species (molecular mass below 2000 g mol − 1 ) have highlighted the existence of J couplings operating via clearly nonbonded interactions and known as “through-space” couplings. Interactions of this type are frequently reported and couplings involving 19 F, 13 C, 77 S…
One-bond 1 J (15 N,H) coupling constants at sp2 -hybridized nitrogen of Schiff bases, enaminones and similar compounds: A theoretical study
2020
1 J(15 N,H) coupling constants for enaminones and NH-forms of intramolecularly hydrogen-bonded Schiff bases as model compounds for sp2 -hybridized nitrogen atoms are evaluated using density functional theory (DFT) to find the optimal functionals and basis sets. Ammonia is used as a test molecule and its one-bond coupling constant is compared with experiment. A methylamine Schiff base of a truncated molecule of gossypol is used for checking the performance of selected B3LYP, O3LYP, PBE, BHandH, and APFD density functionals and standard, modified, and dedicated basis sets for coupling constants. Both in vacuum and in chloroform, modeled by the simple continuum model of solvent, the modified b…
Exploiting Palladium-Catalyzed Cross-Coupling for the Synthesis of 2-Aryl-Substituted 1-Aminocyclopropylphosphonates
2015
A series of 2-aryl-substituted 1-aminocyclopropylphosphonates containing an additional remote phosphonate group have been synthesized starting from readily accessible dimethyl (1 R *,2 R *)-2-(4-bromophenyl)-1-formamidocyclopropylphosphonate using cross-coupling methodology. Different types of palladium-catalyzed reactions for carbon–carbon and carbon–phosphorus bond formation were realized. In each case the optimum conditions were found to obtain the desired products in high yield in both small- and large-scale experiments.
ChemInform Abstract: “Through-Space” Nuclear Spin-Spin Couplings in Ferrocenyl Polyphosphanes and Diphosphino Cavitands: A New Way of Gathering Struc…
2010
Abstract Nuclear magnetic resonance is an invaluable technique for investigating a variety of important issues ranging from the determination of molecular structure to therapeutic medical imaging. In this respect, the indirect nuclear spin–spin coupling involving common nuclei such as 1 H, 13 C or 31 P provides, via the J constant, conclusive data for compound characterization in solution. This electron-mediated nuclear spin coupling is usually regarded as being transmitted by covalently bonded magnetic atoms. However, several experimental and theoretical studies, first focused on constrained organofluorides, and more recently devoted to phosphane ligands highlighted the existence of very i…
A Microscopic Interpretation of Pump–Probe Vibrational Spectroscopy Using Ab Initio Molecular Dynamics
2018
What happens when extra vibrational energy is added to water? Using nonequilibrium molecular dynamics simulations, also including the full electronic structure, and novel descriptors, based on projected vibrational density of states, we are able to follow the flow of excess vibrational energy from the excited stretching and bending modes. We find that the energy relaxation, mostly mediated by a stretching-stretching coupling in the first solvation shell, is highly heterogeneous and strongly depends on the local environment, where a strong hydrogen bond network can transport energy with a time scale of 200 fs, whereas a weaker network can slow down the transport by a factor 2-3.
Understanding charge transport in wavy 2D covalent organic frameworks
2021
Understanding charge transport in 2D covalent organic frameworks is crucial to increase their performance. Herein a new wavy 2D covalent organic framework has been designed, synthesized and studied to shine light on the structural factors that dominate charge transport.
Breakup and default risks in the great lockdown
2023
Abstract In this paper, we exploit CDS quotes for contracts denominated in different currencies and with different default clauses to estimate the risk of a breakup of the Eurozone and the propagation of breakup and default risks after the COVID-19 shock. Our main result is that the risk of a Eurozone breakup is significant although, quantitatively, it is not larger than in the period before the COVID-19 shock. In addition, we find that an increase in the redenomination risk in one country is associated with an increase in default premia and bond spreads in other Eurozone countries. Finally, we find that a sizeable fraction of the changes in the cost of insuring against redenomination and d…
A Numerical Study to Predict the Mechanical Response of FRCM Composites
2022
Fabric Reinforced Cementitious Matrix (FRCM) materials are increasingly common for strengthening existing masonry structures. Their popularity is due to their many advantages with respect to resin-based composites, especially when applied to stone supports. The constitutive behaviour of FRCM materials is defined by the combination of their tensile response and the bond behaviour with the masonry support, both depending on complex stress transfer mechanisms between matrix and fabric, especially in the post-cracking stage. This paper presents a numerical study which aims to predict the mechanical behaviour of FRCM systems through simple 2D models of truss elements and non-linear springs to si…