Search results for "bond"
showing 10 items of 3527 documents
Covalent and non-covalent chemistry of 2D black phosphorus
2021
The post-graphene era is undoubtedly marked by two-dimensional (2D) sheet polymers, such as black phosphorus (BP). This emerging material has a fascinating structure and outstanding electronic properties and has been postulated for a plethora of applications. The need to circumvent the pronounced oxophilicity of P atoms has dominated the research on this material in recent years, with the objective of finding the most effective method to improve its environmental stability. When it comes to chemical functionalization, the few approaches reported so far involve some drawbacks such as low degree of addition and low production ability. This review presents the concepts and strategies of our st…
Does glycosyl transfer involve an oxacarbenium intermediate? Computational simulation of the lifetime of the methoxymethyl cation in water
2011
2D free-energy surfaces for transfer of the methoxymethyl cation between two water molecules are constructed from molecular dynamics (MD) simulations in which these atoms are treated quantum-mechanically within a box of 1030 classical solvent water molecules at 300 K. This provides a simple model for glycosyl transfer in water. The AM1/TIP3P surfaces with 2D-spline corrections at either MPWB1K/6-31+G(d,p) or MP2/6-31+G(d,p) contain a shallow free-energy well corresponding to an oxacarbenium ion intermediate in a DN*AN mechanism. MD analysis at three temperatures leads to a classical estimate of the lifetime of the methoxymethyl cation in water; when quantum corrections for vibrational zero-…
Photochemical window mechanism for controlled atom release in carborane endohedral boxes: Theoretical evidence
2006
Abstract On the basis of high-level quantum chemical calculations, closed-cage carboranes are shown to be prospective nanoscale mass selective conveyors via a photochemical switch. A mechanism is evidenced in which stable carborane boxes with lithium as endohedral atom, Li@CB 11 H 12 , can be photoinduced to sequentially evolve opening the cage, releasing the internal atom through a window in the box structure, and closing the cage toward either ionic or neutral channels where the charge or spin of the fragments may be controlled.
Theoretical spectroscopic parameters of the alkali monofluorides LiF, NaF and KF
1992
Abstract Multireference configuration interaction and second-order perturbation theory are used to determine accurate spectroscopic parameters for the ground state of the alkali monofluorides from LiF to KF. Systematic saturation of the spdf subspaces of the atomic basis sets for the electron affinity of fluorine and the ionization potential of the metals have been shown to be more efficient than for the approximate dissociation energies in the molecule. the calculated rotational and vibrational constants and transitions for the three systems show excellent agreement with the expeirmental data.
Mono- and Tripodal Porphyrins: Investigation on the Influence of the Number of Pyrene Anchors in Carbon Nanotube and Graphene Hybrids.
2020
A series of molecular precursors, containing one (1 and 3) or three (2 and 4) pyrene anchors, covalently linked to porphyrins (free base or Zn), were prepared and characterized. All of them enable ...
Hartree–Fock study of adhesion and charge redistribution on the Ag/MgO(0 0 1) interface
2001
Abstract Ab initio study of the Ag/MgO(0 0 1) interfaces based on a quantitative analysis of the bonding in the interfacial region is provided in the framework of Hartree–Fock approach. We are describing the way interfacial electronic and other properties evolve as a function of metal coverage. General conclusion that could be drawn from our calculations is that chemical bond formation is not important for the Ag/MgO(0 0 1) perfect interface. Physisorption of Ag atoms over surface O 2− ions associated with atomic polarization and charge redistribution in the metal planes are the dominant effects. The adhesion energy is enhanced by the interaction of the substrate Mg 2+ ions with the surplus…
Structure, magnetizability, and nuclear magnetic shielding tensors of bis-heteropentalenes. IV. Dihydrophospholophosphole isomers
2005
The geometry of the heteropentalenes formed by two phosphole units has been determined at the DFT level. The magnetic susceptibility and the nuclear magnetic shielding at the nuclei of these systems have also been calculated using gauge-including atomic orbitals and a large Gaussian basis set to achieve near Hartree-Fock estimates. A comparative study of the various isomers, of their flattened analogs, and of the parent phosphole molecule, shows that the [3,4-c] isomer is the most aromatic system in the set considered, assuming diatropicity and degree of planarity as indicators, even if it is the less stable in terms of total molecular energy. Plots of magnetic field-induced current densiti…
Structure optimization of azobenzene oligomers for holography
2005
Azobenzene oligomer layers with side chain chromofore groups (ChG) has been experimentally studied to optimize scalar and vector hologram recording at 633 nm. ChG with different acceptors (Br, NO2, H, CN) and different bonding type to the matrix (dispersed without bonding or with covalent bonding) were used. The influence of oligomer matrix (polyvinylbuthirol, tolyle, hexamethylene, polyvinylpirolidone, double matrix) and spacers was also studied. The best results (the maximal diffraction efficiency of 7.9% and the minimal specific recording energy of 0.38 J/(cm2 %)) are obtained for ChG with one NO2 acceptor group covalently bonded to tolyle matrix. Double matrix considerably decreases the…
A triclinic polymorph of (−)-(S)-N-benzyl-2-[(R)-6-fluorochroman-2-yl]-2-hydroxyethanaminium bromide
2013
The title salt, C18H21FNO2+·Br−, determined at 115 K, crystallizes in the triclinic space groupP1. The previously reported polymorph occurs in the monoclinic space groupP21and has two independent molecules in the asymmetric unit [Peeterset al.(1993).Acta Cryst.C49, 2157–2160]. In the title molecule, the pyran rings adopt half-chair conformations. The absolute configuration isSfor the hydroxy-bearing C atom andRfor the asymmetric C atom in the dihydropyran unit. In the crystal, the components are linked by N—H...Br and O—H...Br hydrogen bonds, forming chains along thec-axis direction. The crystal studied was refined as an inversion twin.
Solute-induced Water Structure: Computer Simulation on a Model System
1988
Abstract Two series of Monte Carlo simulations have been carried out on a system consisting of 125 water molecules, one of which is kept fixed to simulate a water molecule whose mobility is restricted by a solute. The results are checked against similar simulations without restrictions, used as a control, and they show how the blocked molecule helps increase both the structural order and the connectivity of the hydrogen bond network. Cooperativity originating from proton polarizability of H-bonds and/or from many-body terms of interaction potentials cannot be involved since we use a rigid water model and ab initio pair potentials. The present findings are interpreted as indicative of a moti…