Atomic charge difference parameter

Transferability of atomic densities was tested by Brock et al. (1991), who applied atomic charge density parameters from an accurate low-temperature study of perylene (I) to data collected at five and six different temperatures on naphthalene (II) and anthracene (III), respectively. The molecules are all aromatic hydrocarbons. To reduce the number of variables, all H atoms were assigned... 

Indeed, both expressions predict quadratic dependence of AA on the dipole moment of the solute. As in the previous example, it is of interest to test whether this prediction is correct. Such a test was carried out by calculating AA for a series of model solutes immersed in water at different distances from the water-hexane interface [11]. The solutes were constructed by scaling the atomic charges and, consequently, the dipole moment of a nearly spherical molecule, CH3F, by a parameter A, which varied between 0 and 1.2. The results at two positions - deep in the water phase and at the interface - are shown in Fig. 2.3. As can be seen from the linear dependence of A A on p2, the accuracy of the second-order perturbation theory... 

The models which we have developed can be classified as follows. Some are intended to represent physicochemical processes and properties by mimicking quantitatively concepts which have become accepted by chemists in general. A simple example would be the transfer of electronic charge between two atoms of differing electronegativities. Other models are statistical in nature. We have applied parameters quantified by the physicochemical models to series of chemical data. The relationships thus derived by various statistical techniques, and their form, is such that they are readily applicable to the task of quantifying the evaluation process in EROS. Further discussion of these points is a major feature of this article. 

At a quite different level of approximation, this class of compounds was investigated by means of STO-3G calculations involving a detailed optimization of all the geometric and exponent parameters [42]. The Mulhken net atomic charges and the... 

Figure 2.32 Order parameters calculated for (a) anthracene and (b) anthraquinone dissolved in nematics with different dielectric anisotropy [9]. For the case Ae > 0, the results obtained in the absence of induction effects are also shown (dotted line). The temperature dependence of the dielectric anisotropy is taken into account, with the values eNI = 10.2, AeN/ = 8 and eNI = 5.2, AeN/ = —0.5 for the two cases at the nematic-isotropic transition. Atomic charges in absolute value greater than 0.1 are shown (in e units). The y axis is perpendicular to the molecular plane.

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