Refractive Index and Molar Refractivity

The refractive index of RTILs at the sodium D-line (589 nm), is available for a large number of the RTILs dealt with in this book. The data for 298.15 K are show in Table 6.10, rounded if necessary to four decimals, the variation between the reported data of diverse authors being often as large as 0.0005. The values are within a narrow range 1.37 1-57, while RTILs with cyano-groups in the 

Group contribution schemes have been proposed for the estimation of the refractive index of RTILs. Sattari et al. proposed for Eq. (6.29) that a( D) = 1 -5082 + rijaj and b no) = -1.4207 x + Yjijbj [330], where rij is the number of functional groups of the / -th kind and a, and bj are their listed values. 

The molar refractions of RTILs are given by the Lorentz-Lorenz expression  

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USES FOR REFRACTIVE INDEX AND MOLAR REFRACTION DATA... 

The importance of specific volume or density in determining refractive index is apparent in Equations 1 and 2, which are used in calculating refractive index and molar refraction. This inverse relationship between specific volume and refractive index is illustrated in Table n (cf. columns 2 and 4). The necessity of obtaining an accurate value for the specific volume of a protein in order to obtain agreement between its refractive index calculated from the amino acid composition and the determined value can be illustrated in the case of ribonu-... 

Effect of Ionization on the Refractive Index and Molar Refraction of Amino Acids and Proteins. Since the electrostriction produced by an amino acid does not affect its molar refraction, the ionization of an amino acid might be expected to produce no significant change in molar refraction. Table V indicates that this is the case, provided the large change in the volume of the amino acid as a result of ionization, found by Kauzmann, Bodanszky, and Rasper (23), is used in calculating molar refraction. The refractive index of an equivalent concentration of hy-... 

Table V. Effect of Ionization on the Refractive Index and Molar Refraction of Alanine and Ovalbumin 25° (A - 589 mp)...

Shirao K, Fujii Y, Tominaga J et al (2002) Electronic polarizabilities of Sr " " and Ba " " estimated from refractive indexes and molar volumes of molten StCL and BaQ2. J Alloys Comp 339 309-316... 

Vieillard P (1987) A new set of values for Pauling s ionic radii. Acta Cryst B43 513-517 Iwadate Y, Fukushima K (1995) Electronic polarizability of a fluoride ion estimated by refractive indexes and molar volumes of molten eutectic LiF-NaF-KF. 1 Chem Phys 103 6300-6302... 

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. ... 

Fundamental Limitations to Beers Law Beer s law is a limiting law that is valid only for low concentrations of analyte. There are two contributions to this fundamental limitation to Beer s law. At higher concentrations the individual particles of analyte no longer behave independently of one another. The resulting interaction between particles of analyte may change the value of 8. A second contribution is that the absorptivity, a, and molar absorptivity, 8, depend on the sample s refractive index. Since the refractive index varies with the analyte s concentration, the values of a and 8 will change. For sufficiently low concentrations of analyte, the refractive index remains essentially constant, and the calibration curve is linear. 

The subscripts 1,2,3 refer to the main solvent, the polymer, and the solvent added, respectively. The meanings of the other symbols are n refractive index m molarity of respective component in solvent 1 C the concentration in g cm"3 of the solution V the partial specific volume p the chemical potential M molecular weight (for the polymer per residue). The surscript ° indicates infinite dilution of the polymer. 

The Lorentz-Lorenz equation [2] defines the molar refraction, RD, as a function of the refractive index, density, and molar mass ... 

The application of refractive index and differential viscometer detection in SEC has been discussed by a number of authors [66-68]. Lew et al. presented the quantitative analysis of polyolefins by high-temperature SEC and dual refractive index-viscosity detection [69]. They applied a systematic approach for multidetector operation, assessed the effect of branching on the SEC calibration curve, and used a signal averaging procedure to better define intrinsic viscosity as a function of retention volume. The combination of SEC with refractive index, UV, and viscosity detectors was used to determine molar mass and functionality of polytetrahydrofuran simultaneously [70]. Long chain branching in EPDM copolymers by SEC-viscometry was analyzed by Chiantore et al. [71]. 

The interaction between a glass and light is related to the susceptibility of displacement of electrical charge, which in turn is related to the polarizability. Ionic polarizability increases with the size of ions involved however, structural considerations are also important. Refractive index (see Table 1), dielectric constant, polarizability, and molar volume are related in the molar refractivity, Rm. 

An application of continuum solvation calculations that has not been extensively studied is the effect of temperature. A straightforward way to determine the solvation free energy at different temperatures is to use the known temperature dependence of the solvent properties (dielectric constant, ionization potential, refractive index, and density of the solvent) and do an ab initio solvation calculation at each temperature. Elcock and McCammon (1997) studied the solvation of amino acids in water from 5 to 100°C and found that the scale factor a should increase with temperature to describe correctly the temperature dependence of the solvation free energy. Tawa and Pratt (1995) examined the equilibrium ionization of liquid water and drew similar conclusions. An alternative way to study temperature effect is through the enthalpy of solvation. The temperature dependence of is related to the partial molar excess enthalpy at infinite dilution,... 

The refractive index is usually estimated in terms the molar refraction R, which quantifies the intrinsic refractive power of the structural units of the material. Several definitions have been proposed for R. Two of these definitions incorporate both of the key physical factors determining the refractive index, and are thus especially useful. Equation 8.5 expresses n in terms of the molar refraction RT T according to Lorentz and Lorenz [1,2], and Equation 8.6 expresses n in terms of the molar refraction Rgd according to Gladstone and Dale [3]. 

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