Electron density measurement

Carbo R, L Leyda and M Arnau 1980. An Electron Density Measure of the Similarity Between Tw Compounds. International Journal of Quantum Chemistry 17 1185-1189. 

In the Atoms In Molecules approach (Section 9.3), the Laplacian (trace of the second derivative matrix with respect to the coordinates) of the electron density measures the local increase or decrease of electrons. Specifically, if is negative, it marks an area where the electron density is locally concentrated, and therefore susceptible to attack by an electrophile. Similarly, if is positive, it marks an area where the electron density is locally depleted, and therefore susceptible to attack by a... 

This definition leads to an electron density measured in electrons per nm3 (cf. Sect. 7.10.1). If we are aiming at a treatment in terms of scattering cross-section we define /o = Zre, instead. 

In their model, N is the local electron density measured over an appropriate volume, which they argue is given by the Mott criterion discussed in Sect. 3.4.1. Thus, with the Mott radius of 20 A for uniform spheres, these spheres will constitute the appropriate volume over which to measure the local electron density N. 

Garbo, R., Leyda, L., and Arnau, M. How similar is a molecule to another An electron density measure of similarity between two molecular... 

It is apparent from work published to date that the chemical shifts of C-2, C-3 and C-4 offer a means of distinguishing the different classes of flavonoids. A report on the electronic structure of parent flavonoid compounds compares observed chemical shifts with the values calculated from electron-density measurements with quite good agreement . 

Cylindrical tube with ring electrodes Silane decomposition and dispersion Plug flow with axial dispersion Mean electron density measured with interferometry 71... 

Inductive coupling to quartz tube Silicon nitride from silane- n2 No specific chemistry Plug flow Mean electron density measured with microwave interferometry 72... 

Some Selected References on Electron-Density Measurements in Crystals of Inorcanic Compounds and Metals... 

The authors would like to thank J. Irby for electron density measurements, A. Hubbard for electron temperature measurements and the Alcator C-Mod operations groups for expert running of the tokamak. Work supported at MIT by DoE Co-operative Agreement No. DE-FC02-99ER54512. This work was performed under the auspices of the U.S. Department of Energy by the University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48. 

Most trisulfanes adopt a trans conformation with a local symmetry of C2 for the central X-S-S-S-X unit (motif ++ or —). The term trans describes the position of the two substituents X with respect to the plane defined by the three sulfur atoms. Dicyanotrisulfane is the exception to the rule since this molecule adopts a cis conformation in the solid state, which seems to be the result of the weak interaction of the two nitrogen atoms with the central sulfijr atom of a neighboring molecule. The motif of S3(CN)2 is H— (or —F for the enantiomer see Enantioselectivity), which is present in equal amounts in the unit cell). Electron density measurements on gaseous Me2S3 have been interpreted by a mixture of mainly trans- and little cfr-Me2S3. ... 

Carb6, R., Leyda, L. and Amau, M. (1980). How Similar is a Molecule to Another An Electron Density Measure of Similarity Between Two Molecular Structures. Int.JQuant.Chem., 17, 1185-1189. 

Carbo R, Leyda L, Arnau M. An electron density measure of the similarity between two compounds. Int J Quantum Chem 1980 17 1185-1189. 

Fig. II.2. Water is used to illustrate the atomic coordinate systems used in the additivity scheme for atom susceptibilities. Also shown are contour lines for the overall electron density measured in units of electrons per cubic atomic unit (ao = 0.529 A). The contour lines have been taken from Streitwieser, Andrew, Jr., Owens. Peter H. Orbital and electron density diagrams. New York McMillan and Co. 1973...

Sherry (56, 57) showed that the ion-exchange properties of Na-Y and Na-X zeolite were consistent with 16 Na atoms in the sodalite cage. Since Na scatters x-rays rather similarly to H20 molecules, the presence of 16 Na atoms is consistent with the electron density measurements. 

At high contrast there is only a parallel shift of the scattering curves (triangles and empty circles in Fig. 21). This would point to a homogeneous radial electron density. Measurements in the vicinity of the match point, however, show that the swollen particles cannot be homogeneous at positive contrast the extrema of the curves are shifted away from the ordinate whereas beyond the match point... 

Molecule to Another An Electron Density Measure of Similarity Between Two Molecular... 

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