Refractive constant

The refractive constant or specific refractive index computed by the Lorenz-Lorentz formula,... 

Other investigations include the refraction constants,1 and the dissociation-pressure of the water of crystallization of the dodecahydrate at the transition-point2 and such properties of solutions as density,3 specific heat,4 boiling-point,5 vapour-pressure,6 molecular depression of the freezing-point,7 electric conductivity,8 and hydrolytic dissociation.9... 

The dieleetrie eonstant also eorrelates with refractive index. In the case of aliphatic hydrocarbons, the dielectric constant increases slightly as refraetive index inereases. Both aromatie and aliphatie hydroearbons have dieleetrie eonstants whieh follow the relationship np. The dieleetrie eonstants of aleohols, esters and ketones deerease as the refractive constants increase but only aleohols and ketones form a similar relationship. The dieleetrie eonstants of ketones poorly eorrelate wifli their refractive indiees. 

We have seen that relaxor ferroelectric PLZT ceramics, with compositions (a/65/35) with 7frequency-dependent paraelectric (or relaxor) to long-range ferroelectric phase transition. PLZT (9.5/65/35) ceramics undergo this phase change around 5°C. However, no evidence of this phase change is seen in figure 13. This is likely because the specific refractivity of materials R, which is a measure of the electronic polarization, is unaffected by this particular phase transition. This refractivity constant is defined by the Lorentz-Lorenz relation ... 

X Atomic refractive constant of X Refractive index nF) Surface tension (y) 20°C (vapor)... 

Figure Bl.18.6. Schematic representation of Zemike s phase contrast method. The object is assumed to be a relief grating in a transparent material of constant index of refraction. Phase and amplitude are varied by the Zemike diaphragm, such that an amplitude image is obtained whose contrast is, m principle, adjustable.

The Hamaker constant can be evaluated accurately using tire continuum tlieory, developed by Lifshitz and coworkers [40]. A key property in tliis tlieory is tire frequency dependence of tire dielectric pennittivity, (cij). If tills spectmm were tlie same for particles and solvent, then A = 0. Since tlie refractive index n is also related to f (to), tlie van der Waals forces tend to be very weak when tlie particles and solvent have similar refractive indices. A few examples of values for A for interactions across vacuum and across water, obtained using tlie continuum tlieory, are given in table C2.6.3. 

Here, k is a factor which converts to units (kcal/mol in this case where the distances are in A and the polarisabilities in A ). G, and Gj are constants chosen to reproduce the well depths for like-with-like interactions. The atomic polarisability values are obtained from an examination of appropriate molecular experimental data (such as measurements of molar refractivity). 

The b.p., density and refractive Index are valuable constants for the final characterisation of liquid esters. 

Determination of the physical constants and the establishment of the purity of the compound. For a solid, the melting point is of great importance if recrystalhsation does not alter it, the compound may be regarded as pure. For a hquid, the boiling point is first determined if most of it distils over a narrow range (say, 1-2°), it is reasonably pure. (Constant boUing point mixtures, compare Section 1,4, are, however known.) The refractive index and the density, from which the molecular refractivity may be calculated, are also valuable constants for liquids. 

The refractive index of a liquid is recorded as where t is the temperature at which the measurement is made, and D refers to the wave length of the D line of sodium. As already pointed out, it is usual to determine both the refractive index and the density of the liquid at 20° in any case they should be determined at the same temperatme. These two constants are useful in assisting the characterisation of a pure hquid they are particularly valuable for ahphatic hydrocarbons and similar compounds where the methods of characterisation by the formation of solid derivatives are not entirely satisfactory. 

The values for the D sodium line of the atomic and structural constants and of the bond refractions, as determined by the author, are collected in Tables XI,2A and XI,2B respectively. 

Solvents exert their influence on organic reactions through a complicated mixture of all possible types of noncovalent interactions. Chemists have tried to unravel this entanglement and, ideally, want to assess the relative importance of all interactions separately. In a typical approach, a property of a reaction (e.g. its rate or selectivity) is measured in a laige number of different solvents. All these solvents have unique characteristics, quantified by their physical properties (i.e. refractive index, dielectric constant) or empirical parameters (e.g. ET(30)-value, AN). Linear correlations between a reaction property and one or more of these solvent properties (Linear Free Energy Relationships - LFER) reveal which noncovalent interactions are of major importance. The major drawback of this approach lies in the fact that the solvent parameters are often not independent. Alternatively, theoretical models and computer simulations can provide valuable information. Both methods have been applied successfully in studies of the solvent effects on Diels-Alder reactions. 

A number of properties can be computed from various chemical descriptors. These include physical properties, such as surface area, volume, molecular weight, ovality, and moments of inertia. Chemical properties available include boiling point, melting point, critical variables, Henry s law constant, heat capacity, log P, refractivity, and solubility. 

Table 5.19 Refractive Index, Viscosity, Dielectric Constant, and Surface Tension...

VISCOSITY, SURFACE TENSION, DIELECTRIC CONSTANT, DIPOLE MOMENT, AND REFRACTIVE INDEX... 

Temp., °C Refractive index, Viscosity, mN Dielectric constant, e Surface tension, mN s ... 

---