Electron-density analysis

These electron densities provide detailed information that gives important insight into the fundamentals of molecular structure and a better understanding of chemical reactions. The results of electron density analysis are used in a variety of applied fields, such as pharmaceutical drug discovery and biotechnology. 

From the early advances in the quantum-chemical description of molecular electron densities [1-9] to modem approaches to the fundamental connections between experimental electron density analysis, such as crystallography [10-13] and density functional theories of electron densities [14-43], patterns of electron densities based on the theory of catastrophes and related methods [44-52], and to advances in combining theoretical and experimental conditions on electron densities [53-68], local approximations have played an important role. Considering either the formal charges in atomic regions or the representation of local electron densities in the structure refinement process, some degree of approximate transferability of at least some of the local structural features has been assumed. 

Electroneutrality may also be implemented by imposing the requirement that F(000) equal the number of electrons in the unit cell. The equation F(000) = ne can be treated as an observation, with a weight sufficient to keep the crystal practically neutral, but sufficiently small such as not to dominate the least-squares treatment. This slack constraint (Pawley 1972) has been applied in electron density analysis by Hirshfeld (1977). 

The situation changes, however, if the electronegativity of the group X increases drastically as in the series X = NH2+, OH+, F+ 9. n-Back donation is stepwise decreased to zero and n-complexes are formed. This has been demonstrated via the electron density analysis,which reveals that convex bent bonds change into concave (inwardly curved) bent... 

From the electron density analysis it becomes clear that the cyclopropyl group is an electronic chameleon that can adjust to the different electron delocalization situations. Of course the real reason for this flexibility of the cyclopropyl group stems from the phenomenon of surface delocalisation (see Chapter 2 of this volume)27 85. The three CC bonds of... 

Table 9 Lithium Charges (electrons) in Methyllithium Oligomers as Obtained by Three Methods of Electron Density Analysis ...

The electron density analysis within the AIM methodology shows the presence of bond critical points due to the formation of the HB and, in some homochiral dimers, also between oxygen atoms of different molecules (Fig. 3.13). The presence of the latter bcps is associated to those complexes where the homochiral complex is more stable than the heterochiral one. 

R. Binachi et al., Experimental electron density analysis of MN2(CO)10 Metal-metal and metal-ligand bond characterization. Inorg. Chem. 39, 2360-2366 (2000)... 

De Bondt HL, Blaton NM, Peeters OM et al (1991) Electron density analysis of the antimicrobial drugs and radiosensitizer dimetridazole at 205 K. In Jeffrey GA, Piniella JF (eds) The application of charge density research to chemistry and drug desing. Plenum Press, New York... 

ELECTRON DENSITY ANALYSIS OF ISOLATED AND INTERACTING REACTIVE REGIONS OF MOLECULES... 

A reaction mechanism for the replacement of the endocyclic sulfur atom by the transition metal in these Tt-sulfuranes was given by Manabe et al. on the basis of frontier electron density analysis [282] (see Figure 4.95). Iwasaki explained the mechanism on the energetically less favourable isomer featuring S-S rather than S-N bonds. 

The alternative approach is to count the number of electrons in an atom s space. The question is how to define the volume an individual atom occupies within a molecule. The topological electron density analysis (sometimes referred to as atoms-in-molecules or AIM) developed by Bader uses the electron density itself to partition molecular space into atomic volumes. 

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