Polarizability group molar volumes

The simplest structural descriptors are just the number of carbon atoms, or molecular weight, that is linearly related to the increase in gas chromatographic retention among a homologous series of compounds. This simple relationship led to the development of the Kovits retention index scale. A linear relationship between Kovits retention index and carbon number for homo-logues has been shown to hold for a number of chemical groups. Molar volume, molar refractivity, and molecular polarizability are other simple descriptors of molecular bulk that have been used in QSRR studies. 

A number of useful properties of the Group 1 elements (alkali metals) are given in Table 8. They include ionization potentials and electron affinities Pauling, Allred-Rochow and Allen electronegativities ionic, covalent and van der Waals radii v steric parameters and polarizabilities. It should be noted that the ionic radii, ri, are a linear function of the molar volumes, Vm, and the a values. If they are used as parameters, they cannot distinguish between polarizability and ionic size. 

MR still is the chameleon [91] amongst the physicochemical parameters, despite its broad application in QSAR studies. It has been correlated with lipophilicity, molar volume, and steric bulk. Of course, due to its MW/q component it is indeed related to volume and size of a substituent. But two recent statements that MR is only based on these properties [91, 291] cannot be accepted. The refractive index-related correction term in MR accounts for the polarizability and thus for the size and the polarity of a certain group [158, 173, 286]. The larger the polar part of a molecule is, the larger its MR value will be. Even hydrophobic substituents have a weak enthalpic interaction due to dispersion forces, in addition to their entropic... 

The low polarizability provided by the aUcychc Epiclon moieties leads to Pis with low refractive index. The ellipsometricaly measured values listed in Table 2 show that refractive indices of this type of Pis measured at 632.8 nm correspond to transparent materials, i.e. 1.6-1.7, and are in good agreement with theoretical estimations based on molar refraction and molar volume derived from group contributions theory [29,36]. This approach is based on the assumption that the molar volume, Vu, and the molar refraction, Ru, of the chain repeating unit are additive functions of composition ... 

Molecular polarizability and molar refractivity are closely related properties that provide a measure of a molecule s susceptibility to becoming polarized. These descriptors are often useful in situations where dipole-induced dipole and dispersion interactions play an important role. They are readily calculated from refractive index and molar volume however, applications in QSAR and QSPR usually employ empirical estimates based on atomic, bond, or group contributions. A paper by Miller includes a review of techniques that have been used to estimate molecular polarizabilities. Methods for estimating molar refractivity may be found in the literature. ... 

Despite its higher polarizability and critical temperature, propane is a much poorer solvent than ethylene for this copolymer (see table 3.4). It is the polar interactions between ethylene, which has a quadrupole moment, and the methyl acrylate groups in the backbone of the copolymer, which have dipole moments, that dominate free volume effects. There is no significant difference between the molar densities of propane and ethylene at the temperatures and... 

Experiments confirmed that the molar mass or long chain branching in the above-mentioned samples [166] does not influence the HPLC separation. Independence of the elution volumes on the molar mass >15-20 kg/mol was also found for PE [164] and EP, EB, EO and ethylene/l-decene copolymers [161]. It is typical for adsorption phenomena that adsorption depends on the shape of a molecule, on positions and numbers of functional groups, on polarizability of the molecule, as well as on the type and nature of the sorbent and the solvents. Fine tuning of the adsorptive interactions enables one to reach extremely sensitive and specific chromatographic separations. This represents an additional advantage of HPLC in... 

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