Polarity descriptors

This also involves flexibility and rigidity descriptors (RB and AP), a size descriptor (MW) and a polarity descriptor (log Pow). It appears that these kinds of descriptors are essential for AGfUs-... 

Table 4.17 summarizes the optimized bond angles xmh and hmh and M—X and M—H hybrid and bond-polarity descriptors for these species. 

Numerous methods have also been developed to determine H, based on molecular connectivity indices (MCIs) and/or polarity descriptors [6]. 

These polarity descriptors combine charge and geometry. Dipole moments are used to model dipole-monopole, dipole-dipole, dipole-induced dipole, and other interactions. Both molecular dipole (fi) as well as bond dipole moments may be defined for neutral molecules. A bond dipole moment due to atoms k and / separated by distance, rki, can be defined as (]i-The topographic electronic index defined in Eq. [12] is another measure (index) of polarity.The sum extends over the number of bonded atoms, N. ... 

The ability of an analyte to take part in polar interactions is normally difficult to characterize by means of a single descriptor. The importance of analyte polarity for retention is clearly demonstrated for isomers in 1956, James [53] related the retention of a series of isomeric xylidines to their dipole moment. However, simple QSRR involving dipole moments and other polarity descriptors are rare. 

A general rule is that QSRR equations are characterized by two kinds of structural descriptors one which accounts for bulkiness of analyte and one which encodes its polar properties [85]. Bulkiness descriptors are always significant in GC on non-polar phases and in reversed-phase HPLC whereas the significance of polar descriptors increases as the polarity of both the stationary phases and the analytes increases [7,12],... 

From the literature there is evidence that in GC on polar phases and in normal-phase (adsorption) liquid chromatography (HPLC and TLC) the chemically specific, molecular size-independent intermolecular interactions play the main retention-determining role. For example, the HPLC retention parameters determined for substituted benzenes on porous graphite are described by QSRR equations comprising polarity descriptors but containing no bulk descriptors [93-95]. Because, in general, it is difficult to quantify the polarity properties precisely, the QSRR for GC on polar phases and for normal-phase HPLC are usually of lower quality than in the case of GC on non-polar phases and in the case of reversed-phase liquid chromatography. 

Dewar resonance energy -> resonance indices DFT-based descriptors - quantum-chemical descriptors diagonal matrix -> algebraic operators diagonal operator -> algebraic operators (O diagonal matrix) dielectric constant electric polarization descriptors dielectric susceptibility electric polarization descriptors... 

Many quantum-chemical descriptors are derived from the charge distribution in a molecule or the electron density of specified atoms or molecular regions, and from conformational energy values such as the Joshi electronic descriptors. Moreover, several -> charge descriptors and -> electric polarization descriptors are obtained from atomic charge estimations. 

Electronic EigenVAIue descriptors EEVA descriptors -> EVA descriptors electronic polarizability electric polarization descriptors electronic polarization - electric polarization descriptors... 

EVtype descriptors -> van der Waals excluded volume method EVwhole descriptors - van der Waals excluded volume method excess electron polarizability -> electric polarization descriptors excess molar refractivity -> molar refractivity expanded distance Cluj matrices -> expanded distance matrices expanded distance indices -> expanded distance matrices expanded distance matrices... 

Kier-Hall solvent polarity index - electric polarization descriptors... 

This term is a measure of the exoergic balance (i.e. release of energy) of solute-solvent and solute-solute dipolarity / polarizability interactions. This term, denoted by n, describes the ability of the compound to stabilize a neighbouring charge or dipole by virtue of nonspecific dielectric interactions and is in general given by -> electric polarization descriptors such as -> dipole moment or other empirical - polarity / polarizability descriptors [Abraham et al, 1988]. Other specific polarity parameters empirically derived for linear solvation energy relationships are reported below. 

Molecular descriptors are usually classified into several classes by a mixed taxonomy based on different points of view. For example, descriptors are often distinguished by their physico-chemical meaning such as - electronic descriptors, - steric descriptors, lipophilicity descriptors, -> hydrogen-bonding descriptors, - shape descriptors, charge descriptors, - electric polarization descriptors, - reactivity descriptors, moreover, on the basis of the specific mathematical tool used for the calculation of the molecular descriptors, - autocorrelation descriptors, -> eigenvalue-based descriptors, -> determinant-based descriptors, - Wiener-type indices, - Schultz-type indices can be distinguished. 

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