Electron groups, refraction

Electron group Refraction Electron group Refraction... 

Table 6.3 Refractions of some electron groups (measured by sodium D line)...

Now Pe is numerically equal to the molar refraction R which is an additive property. It has been shown that P is a property which can be calculated by adding the refractions of various electron groups. Six values for such partial molar refractions are given in Table 6.3. 

Alternative analyses of refractometric data have been proposed, e.g. using G. N. Lewis (1923) ideas of valence and electronic bonding, Fajans and Knorr (1924) and independently Smyth (1925) deduced refractivities for octets and electron groups von Steiger (1921), Denbigh... 

The molar refraction of a substance is approximately the sum of the refractions of the electron groups within it. The molar refraction of NaCl, for example, is the sum of the refractions oftheNa ion and theCl ion.Afew values of the molar refraction appropriate... 

The same argument is applied to electron groups in covalent molecules. The refraction of methane is attributed to the refraction of four equivalent electron groups, the pair bonds between the carbon and hydrogen atoms. Thus for the carbon-hydrogen bond refraction we can assign Rq—u = Then for the C—C bond, we derive a value from the refrac-... 

A table of correlations between seven physicochemical substituent parameters for 90 chemical substituent groups has been reported by Hansch et al. [39]. The parameters include lipophilicity (log P), molar refractivity MR), molecular weight MW), Hammett s electronic parameters (a and o ), and the field and resonance parameters of Swain and Lupton F and R). 

In order to assess the orientational stability of the poled state, the temperature dependence of the dipole mobility of the side groups was examined through dielectric relaxation measurements. (13) No low temperature relaxation below Tg was observed in the frequency range studied (100 Hz-100 kHz). In addition, the dielectric constant was approximately equal to the square of the refractive index, indicating that below T only electronic and no significant orientational contributions to the dielectric displacement are present. Thus, it was expected that a given orientational state of the ensemble would be stable at temperatures significantly below Tg. 

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