Property Mapping

In addition to its undoubted imaging capabilities that give access to structures and thus quantitative height profiles, AFM has also its benefits in mapping surface properties. This unique aspect is discussed only briefly using relevant examples for polymers. 

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Thermodynamic properties such as heats of reaction and heats of formation can be computed mote rehably by ab initio theory than by semiempirical MO methods (55). However, the Hterature of the method appropriate to the study should be carefully checked before a technique is selected. Finally, the role of computer graphics in evaluating quantum mechanical properties should not be overlooked. As seen in Figures 2—6, significant information can be conveyed with stick models or various surfaces with charge properties mapped onto them. Additionally, information about orbitals, such as the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), which ate important sites of reactivity in electrophilic and nucleophilic reactions, can be plotted readily. Figure 7 shows representations of the HOMO and LUMO, respectively, for the antiulcer dmg Zantac. 

Fig. 1. Property map of the WCGP with outline of the AHGZ indioated.

Another aspect of the molecules to examine is their physicochemical properties. A possible major contributor to ligands binding in different orientations is their physicochemical properties mapped to their surface. Consider molecules that are symmetrical with respect to their physicochemical properties mapped to their molecular surface. The molecule might be asymmetrical based on structure, yet symmetrical when examining physical properties. In cases... 

This chapter introduces a number of useful graphical models, including molecular orbitals, electron densities, spin densities, electrostatic potentials and local ionization potentials, and relates these models both to molecular size and shape and molecular charge distributions. The chapter also introduces and illustrates property maps which simultaneously depict molecular size and shape in addition to a molecular property. Properties include the electrostatic potential, the value of the LUMO, the local ionization potential and the spin density. 

Graphical models need not be restricted to portraying a single quantity. Additional information may be presented in terms of a property map on top of an isosurface, where different colors may be used to portray... 

Because the images in this chapter are reproduced in black and white, some of the information they are intended to portray has been lost. This is especially true for property maps, where a spectrum of colors is used to convey the value of a particular property. All images in this chapter have been provided as Spartan files on an accompanying CD-ROM. These are marked by an icon where 4 is the chapter number and y is the number of the Spartan file. 

A more important application of the local ionization potential is as an alternative to the electrostatic potential as a graphical indicator of electrophilic reactivity. This is in terms of a property map rather than as an isosurface. Further discussion is provided later in this chapter. 

The most commonly employed and (to date) most important property map is the electrostatic potential map. This gives the electrostatic potential at locations on a particular surface, most commonly a surface of electron density corresponding to overall molecular size (a size surface). 

To see how an electrostatic potential map (and by implication any property map) is constructed, first consider both a size surface and a particular (negative) potential surface for benzene. 

As discussed earlier in this chapter, the spin density of a radical indicates where its unpaired electron resides. This in turn allows qualitative assessment of radical stability. A radical in which the unpaired electron is localized onto a single center is likely to be more labile than a radical in which the unpaired electron is delocalized over several centers. An even more useful indicator of radical stability and radical reactivity is provided by a so-called spin density map. Like the other property maps considered in this chapter, this measures the value of the property (in this case the spin density) on an electron density surface corresponding to overall molecular size. 

Property Map. A representation or map of a property on top of an Isosurface, typically an Isodensity Surface. Electrostatic Potential Maps, and HOMO and LUMO Maps and Spin Density Maps are useful property maps. 

Graphical Models are introduced and illustrated in Chapter 4. Among other quantities, these include models for presentation and interpretation of electron distributions and electrostatic potentials as well as for the molecular orbitals themselves. Property maps, which typically combine the electron density (representing overall molecular size and shape) with the electrostatic potential, the local ionization potential, the spin density, or with the value of a particular molecular orbital (representing a property or a reactivity index where it can be accessed) are introduced and illustrated. 

The correct structure is predicted for BeO, MgO, and CaO, but for SrO and BaO the predicted coordination number is eight, although the structures found are six coordinate. Crystals adopt the structure that has the most favorable lattice energy, and the failure of the radius ratio concept in this case leads us to examine the assumptions on which it is based. Ionic radii are not known with great accuracy and they change with different coordination numbers (Table 7). Also, ions are not necessarily spherical, or inelastic (see Structure Property Maps for Inorganic Solids) ... 

Electronic Structure of Solids Fluorides Solid-state Chemistry Halides Solid-state Chemistry Macrocyclic Ligands Metallic Materials Deposition Metal-organic Precursors Oxides Solid-state Chemistry Periodic Table Trends in the Properties of the Elements Sol-Gel Synthesis of Solids Sohds Characterization by Powder Diffraction Structure Property Maps for Inorganic Solids Superconductivity Thin Film Synthesis of Solids. 

An attractive, semiempirical application of physical insight into alloy formation is found in classifications of alloy phase data into structure maps, quantum diagrams, and so on (see Structure Property Maps for Inorganic Solids) where a necessarily limited number of coordinates (one to three) must reflect the physical parameters determining the property of interest. An example is given below in the Pettifor map for Ti-Al intermetallics. Further developments in the mapping of intermetallics are due to Ceder. ... 

Borides Sohd-state Chemistry Carbides Transition Metal Solid-state Chemistry Electronic Structure of Sohds Quasicrystals Structure Property Maps for Inorganic Solids Superconductivity Zintl Compounds. 

While solid-state stmctures are readily generated by crystallography, evidence for stmctures in solution is usually generated by spectroscopic techniques. Rotation about the metal metal bond of single-bonded dimers has been studied extensively by NMR and IR (see Structure Property Maps for Inorganic Solids). For example, the complex [Mo(CO)3Cp]2 exists as anti and ganche isomers that interconvert (equation 97). 

Electronic Structure of Main-group Compounds Electronic Stmcture of Organometallic Compounds Magnetism of Extended Arrays in Inorganic Solids Molecular Orbital Theory Solids Computer Modeling Structure Property Maps for Inorganic Solids Superconductivity. 

Sohd-state Chemistry Structure Property Maps for Inorganic Solids. 

Bonding Energetics of Organometallic Compounds Electron Transfer in Coordination Compounds Paramagnetic Organometallic Complexes Structure Property Maps for Inorganic Solids. 

Palladium metal is silvery-white, ductile, and malleable, crystalhzing in the fee structure (see Structure Property Maps for Inorganic Solids). The metal can be made into finely divided forms (including nanoparticles) that are catalytically... 

Tlie Re complexes, generally prepared by X2 oxidative addition to the parent Re species (equation 6), are normally seven coordinate and diamagnetic with a capped octahedron structure, but six-coordinate, 16-electron derivatives have been found, especially with isocyanide ligands. see Structure Property Maps for Inorganic Solids). 

Variable temperature H NMR spectroscopy of a series of Sc and Y metallocene allyl complexes indicates flux-ional (see Fluxional Molecule and Structure Property Maps for Inorganic Solids) behavior involving C-C... 

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