Applications to molecular structures. Recent applications of high resolution n.m.r. to the determination of molecular structure

1962 ◽  
Vol 34 ◽  
pp. 104 ◽  
Author(s):  
J. N. Shoolery
Keyword(s):  
Molecular Structure ◽  
High Resolution ◽  
Molecular Structures

scholarly journals Gas–liquid interactions in solution

2005 ◽  
Vol 77 (3) ◽  
pp. 653-665 ◽  
Author(s):  
M. F. Costa Gomes ◽  
A. A. H. Pádua
Keyword(s):  
Molecular Structure ◽  
Computer Simulation ◽  
Ionic Liquids ◽  
Quantum Chemical ◽  
Molecular Structures ◽  
Gas Solubility ◽  
Free Energies ◽  
Solvent Interactions ◽  
Macroscopic Properties

Two approaches are followed to understand how molecular interactions influence the macroscopic properties of solutions: (1) experiment, through the determination of gas solubility, and (2) computer simulation, used to evaluate microscopic properties (structural and energetic). Examples of application of these approaches are considered in order to explain the properties of solutions containing fluorinated fluids or ionic liquids. The molecular structures and interactions are described by force fields built from ab initio quantum chemical calculations. These models allow the determination of free energies from computer simulations by using appropriate energy routes provided by statistical mechanics. The macroscopic properties related to the process of dissolution of several gases are interpreted in terms of the molecular structure of the solutions and of the solute–solvent interactions.

Unexpected molecular structure from laboratory powder diffraction data

2002 ◽  
Vol 35 (6) ◽  
pp. 669-673 ◽  
Author(s):  
Vladimir V. Chernyshev ◽  
Alexandr V. Yatsenko ◽  
Alexandr M. Kuvshinov ◽  
Svyatoslav A. Shevelev
Keyword(s):  
Molecular Structure ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Molecular Structures ◽  
Grid Search ◽  
Two Dimensional ◽  
Powder Diffraction Data ◽  
Search Technique ◽  
Crystal And Molecular Structures

In the framework of a thorough study of the reactions ofC-(2,4,6-trinitrophenyl)azomethines with various nucleophiles, the crystal and molecular structures of three compounds, namely 2,4-dinitro-N-phenyl-6-(phenylazo)benzamide, (I),N-(2-methoxyphenyl)-2-(2-methoxyphenylazo)-4,6-dinitrobenzamide, (II), andN-methyl-2,4-dinitro-N-phenyl-6-(phenylazo)benzamide, (III), were determined from low-resolution laboratory powder diffraction data. The crystal structure determination of (I), starting from erroneous two-dimensional structures, produced the correct solution as a result of the use of a combination of a systematic grid search and bond-restrained Rietveld refinement. The obtained molecular structure of (I) was quite unexpected. Based on the correct molecular structure of (I), the crystal structures of (II) and (III) were routinely solved by the grid search technique.

To what extent can molecular structure point to potential hazards?

1974 ◽  
Vol 185 (1079) ◽  
pp. 159-164 ◽  
Keyword(s):  
Molecular Structure ◽  
Biological Activity ◽  
Pharmaceutical Industry ◽  
Data Bank ◽  
Molecular Structures ◽  
Comprehensive Index ◽  
Chemical Type

The Ashby Commission reports propose, inter alia , the setting up of a data bank to enable pre-determination of the potential hazards associated with pollutants of known chemical type. The pharmaceutical industry faces a parallel problem with respect to new candidate drugs; and also the converse situation in which it seeks new molecular structures having prescribed (useful) biological activity. The mechanics of establishing such a comprehensive index are discussed, together with the extent, based on specific examples, to which it can be applied to the Ashby proposals.

Determination of the molecular structure of diacetylene from high-resolution FTIR spectroscopy

1995 ◽  
Vol 6 (1) ◽  
pp. 47-55 ◽  
Author(s):  
Rebecca Tay ◽  
Gregory F. Metha ◽  
Finlay Shanks ◽  
Don McNaughton
Keyword(s):  
Molecular Structure ◽  
High Resolution ◽  
Ftir Spectroscopy

High-resolution microscopy of twin boundaries in gold

1987 ◽  
Vol 45 ◽  
pp. 260-261
Author(s):  
William Krakow ◽  
David A. Smith
Keyword(s):  
High Resolution ◽  
Specimen Preparation ◽  
Gold Films ◽  
Boundary Area ◽  
Transmission Electron ◽  
Recent Developments ◽  
Tilt Boundaries ◽  
High Resolution Microscopy ◽  
Twist Boundaries

Recent developments in specimen preparation, imaging and image analysis together permit the experimental determination of the atomic structure of certain, simple grain boundaries in metals such as gold. Single crystal, ∼125Å thick, (110) oriented gold films are vapor deposited onto ∼3000Å of epitaxial silver on (110) oriented cut and polished rock salt substrates. Bicrystal gold films are then made by first removing the silver coated substrate and placing in contact two suitably misoriented pieces of the gold film on a gold grid. Controlled heating in a hot stage first produces twist boundaries which then migrate, so reducing the grain boundary area, to give mixed boundaries and finally tilt boundaries perpendicular to the foil. These specimens are well suited to investigation by high resolution transmission electron microscopy.

High-Resolution Image Simulation of a Tilted Crystal

1990 ◽  
Vol 48 (1) ◽  
pp. 68-69
Author(s):  
C. J. D. Hetherington
Keyword(s):  
High Resolution ◽  
Crystal Thickness ◽  
Thin Specimen ◽  
Atomic Structures ◽  
Kikuchi Lines ◽  
High Resolution Images ◽  
Final Estimate ◽  
Simulated Images ◽  
Habit Planes

Most high resolution images are not directly interpretable but must be compared with simulations based on model atomic structures and appropriate imaging conditions. Typically, the only parameters that are adjusted, in addition to the structure models, are crystal thickness and microscope defocus. Small tilts of the crystal away from the exact zone axis have only rarely been considered. It is shown here that, in the analysis of an image of a silicon twin intersection, the crystal tilt could be accurately estimated and satisfactorily included in the simulations.The micrograph shown in figure 1 was taken as part of an HREM study of indentation-induced hexagonal silicon. In this instance, the intersection of two twins on different habit planes has driven the silicon into hexagonal stacking. However, in order to confirm this observation, and in order to investigate other defects in the region, it has been necessary to simulate the image taking into account the very apparent crystal tilt. The inability to orientate the specimen at the exact [110] zone was influenced by i) the buckling of the specimen caused by strains at twin intersections, ii) the absence of Kikuchi lines or a clearly visible Laue circle in the diffraction pattern of the thin specimen and iii) the avoidance of radiation damage (which had marked effects on images taken a few minutes later following attempts to realign the crystal.) The direction of the crystal tilt was estimated by observing which of the {111} planes remained close to edge-on to the beam and hence strongly imaged. Further refinement of the direction and magnitude of the tilt was done by comparing simulated images to experimental images in a through-focal series. The presence of three different orientations of the silicon lattice aided the unambiguous determination of the tilt. The final estimate of a 0.8° tilt in the 200Å thick specimen gives atomic columns a projected width of about 3Å.

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