Solvents, index of refraction

Indeed, things are slightly more complicated, because the electrons of the solvent can respond on the timescale of the absorption. Thus, in discussing solvent effects, it is helpful to separate the bulk dielectric response of the solvent, which is a function of s, into a fast component, depending on where n is the solvent index of refraction, and a slow component, which is the remainder after the fast component is removed from the bulk. The initially formed excited state interacts with the fast component in an equilibrium fashion, but with the slow component frozen in its ground-state-equilibrium polarization. The fast component accounts for almost the entire bulk dielectric response in very non-polar solvents, like alkanes, and about one-half of the response in highly polar solvents. 

Experimental Study of Effects of Solvent Index of Refraction... 

In general, it may be said that enantiomers have identical properties in a symmetrical environment, but their properties may differ in an unsymmetrical environment. Besides the important differences previously noted, enantiomers may react at different rates with achiral molecules if an optically active catalyst is present they may have different solubilities in an optically active solvent., they may have different indexes of refraction or absorption spectra when examined with circularly polarized light, and so on. In most cases these differences are too small to be useful and are often too small to be measured. 

Assuming in the first instance that the polymer molecules are quite independent, then the situation is analogous to that in the preceding section, except that the scattering molecules (polymer) are now surrounded by solvent molecules of refractive index n0 instead of by free space of refractive index 1.0. The analogue of Eq. (15) becomes... 

The intensity of scattered light or turbidity (t) is proportional to the square of the difference between the index of refraction (n) of the polymer solution and of the solvent ( o), to the molecular weight of the polymer (M ), and to the inverse fourth power of the wavelength of light used (A). Thus ... 

In polar and H-bonding solvents such as acetone, tetrahydrofuran or methanol CgQ is essentially insoluble. It is sparingly soluble in alkanes, with the solubility increasing with the number of atoms. In aromatic solvents and in carbon disulfide, in general appreciable solubilities are observed. A significant increase of the solubility takes place on going from benzenes to naphthalenes. Although there are trends for the solution behavior of Cjq, there is no direct dependence of the solubility on a certain solvent parameter like the index of refraction n. When the solubility is... 

Classification of Solvents using Physical Constants The following physical constants can be used to characterize the properties of a solvent melting and boiling point, vapor pressure, heat of vaporization, index of refraction, density, viscosity, surface tension, depose moment, dielectric constant, polarizability, specific conductivity, and so on. 

These ABA copolymers have an index of refraction of 1.5 and water absorption of about 0.2%. Unless hydrogenated to saturated block copolymers, these unsaturated unstabilized plastics are degraded in sunlight. The polybutadiene domains are attacked by aliphatic hydrocarbon solvents, such as hexane, and the polystyrene domains arc attacked by aromatic hydrocarbon... 

This scheme of frequency tripling was successfully tested with fuchsin in hexafluorisopropanol (a solvent selected for its low index of refraction and relatively flat dispersion curve) to frequency-triple the output of a neodymium laser 67,68) With an input power of 10 MW/cm2 a third-harmonic output of 0.2 mW/cm2 was measured. This low value was mainly due to the relatively high absorption of fuchsin at 355 nm. An improvement of the efficiency by a factor of 80 was found with hexamethylindocarbocyanine iodide in hexafluorisopropanol because of the much lower absorption of this dye at 355 nm. Since the absorption minimum of this dye is at 383 nm, one could expect an additional efficiency increase by a factor of 70 for a fundamental laser wavelength of 1.15 / 69>. Other cyanine dyes have been used for frequency tripling a fundamental wavelength of 1.89 /mi 70>. 

An expression has been derived by Marcus34 and Hush35 for A0 assuming the solvent to be a structureless dielectric continuum characterized by the macroscopic dielectric constants Dop and Ds. D0p and Ds are the optical and static dielectric constants, respectively, and Dop = n2 where n is the index of refraction in the visible spectral region. In the limit that the reactants can be treated as two non-interpenetrating spheres, AQ is given by equation (23). 

A solution of 14 g of the distilled, solid 4-ethoxy-3-methoxyphenol in 20 mL MeOH was treated with a solution of 5.3 g KOH in 100 mL hot MeOH. There was then added 11.9 g methyl iodide, and the mixture was held at reflux temperature for 2 h. The reaction was quenched with 3 volumes H.O, made strongly basic by the addition of 1 volume of 5% NaOH, and extracted with 2x150 mL E O. Pooling the extracts and removal of the solvent under vacuum gave 9.7 g of 2.4-dimethoxy-1-ethoxybenzene as a clear, off-white oil that showed a single peak by GC. An acceptable alternate synthesis of this ether i s the ethylation of 2,4-dimethoxyphenol, whichisdescribedintherecipeforTMA-4. The index of refraction was nD25 = 1.5210. 

Extract the aqueous phase with six 250-m portions of methylene chloride wash the solid cake with three of the portions prior to their use on the solution. Dry the combined extracts over 40 g of anhydrous magnesium sulfate and inhibit with 0.5 g of hydroquinone. Remove the drying agent by filtration and strip the methylene chloride by distillation at atmospheric pressure remove final traces of this solvent by stripping at 20 mm pressure and room temperature. Then separate the mixture of crude vinyl isomers by distillation at reduced pressure. By heating to a pot temperature of 90°C, the 2-methyl-5-vinyltetrazole is conveniently and almost completely removed at 1.0 mm pressure. A well cooled condenser and a receiver chilled in an ice-water bath are needed to prevent loss of the condensate. The weight of once distilled 2-isomer is 89.9 g the index of refraction at 25°C is 1.4814, corresponding to a purity of 97.2 percent. The corrected yield amounts to... 

The fundamental idea is to determine the solubility parameter of the polymer, and then to use tabulated results to identify a number of solvents that have solubility parameters close to this value. The list of potential solvents is then narrowed to two or three candidates. Solvents that are too volatile, too toxic, too flammable, too expensive, and so on can be removed from the list. Other criteria would depend on the nature of the studies to be pursued. If the objective is to carry out light-scattering measurements, the need for maximizing the contrast factor would make the index of refraction of the solvent an additional important consideration. 

The Kamlet-Taft u polarity/polarizability scale is based on a linear solvation energy relationship between the n it transition energy of the solute and the solvent polarity ( 1). The Onsager reaction field theory (11) is applicable to this type of relationship for nonpolar solvents, and successful correlations have previously been demonstrated using conventional liquid solvents ( 7 ). The Onsager theory attempts to describe the interactions between a polar solute molecule and the polarizable solvent in the cybotatic region. The theory predicts that the stabilization of the solute should be proportional to the polarizability of the solvent, which can be estimated from the index of refraction. Since carbon dioxide is a nonpolar fluid it would be expected that a linear relationship... 

At visible frequencies, the change in the solution index of refraction with an added solute gives a qualitative idea of the magnitude of relative polarizability of solute and solvent. As elaborated elsewhere in the text, the complex dielectric response, e = e (a>) + is"(co), is equal to the square of the complex refractive index ( ref + /kabs)2 = (w2ef— Kbs) + 2i reffcabs where nKi is the index of refraction and kabs is the absorption coefficient. In a transparent region where kabs = 0, the dielectric response function e = njref. (See the Level 2.4 essay on dielectric response.)... 

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