Molar Kerr constant

T471), 959 <55ACS847> molar Kerr constant, 3, 947 (65JCS571)... 

Dipole moments and molar Kerr constants of phenotellurazines were measured (85ZOB846). The results suggest a significant shift of electron density from the benzene rings toward the heterocycle. 

The Kerr effect is the birefringence induced in a medium by an external electric field (12). From such an experiment we deduce the molar Kerr constant mK, thus... 

In table I we present the molar Kerr constants and mean square dipole moments of three fluorinated polymers, poly (trifluoroethylene) (PFjE), polylvinylidene fluoride) (PVF2) and poly(fluoromethylene) (PFM), dissolved in p-dioxane. The results show the sensitivity of mK to the degree and type of fluorination varying over an order of magnitude and also changing sign. Calculations of mK and for comparison are in progress (5). 

Figure 1. Molar kerr constant values (x 10 ucm7SC 2mot ) calculatedforpolyfstyrene-co-p-bromostyrene) copolymers as a function of composition Cand tact icily pr Black squares are experimental results. (Reproduced from Ref 3. Copyright 1981, American...

Dipole moment studies and molar Kerr constants, in C6Hi2 at 25 °C, have proved of much use in adducing the conformations of acylpyridines (73JCS(P2)l46l)..4-Formylpyridine is planar, but the acetyl group appears to be twisted about 25° from the plane of the pyridine ring in 4-acetylpyridine. The conformation of 4-benzoylpyridine must be defined by two angles 6 and 4> as in (262). The preferred conformation is calculated to be 6 = = 25°, consistent with the result for 4-acetylpyridine. 

Based on comparison of calculation and experiment for the molar Kerr constants mK and the dipole moments squared of the a,o>-dibromoalkanes lx S 17) in cyclohexane. 

Molar Kerr constants mK and dipole moments squared of polytoxyethylene giycoils (POEG) and polyjoxyethylene dimethyl ether)s (POEDE) are reported in the isotropically polarizable solvents carbon tetrachloride, cyclohexane, and dioxane. Data for mK/x for POEG appear to reach an asymptotical value, Calculations of mK/x and /x based on the RIS model show good agreement with the experimental results. 

Two different RIS models are used to calculate dipole moments and molar Kerr constants for PVB oligomers. The obtained results are compared with experimental results. 

The optical anisotropies y and molar Kerr constants mK of model compounds, and of polylp-chlorostyrene) and polyfp-bromostyrene), are determined. Averages and over all conformations of the polymer chains are calculated as functions of the fraction wm of the meso diads using the RIS model originally developed for PS. 

Experimental values are presented of the molar Kerr constants /x and dipole moments squared, lx, for the copolymers poly(styrene-co-p-bromostyrene), where x is the degree of polymerization. Some results are also presented for poly(styrene-co-p-chlorostyrene) and related polymers. The RIS model of Yoon etal. (Yoon, D. Y. Sundararajan, P. R. Flory, P. J. Macromolecules 1975, 8, 776) is used to calculate mK/x and /x values as a function of tacticity and composition. The statistical weight matrices are identical with those used by Saiz etal. (Saiz, E. Mark, J. E. Flory, P. J. Macromolecules 1977, 10, 967), with the following parameters h = 0.8 exp 397/RT), co = o = 1.3 exp - 1987/RT) and m,= 1.B exp -(2186/RT), where T = 298 K is the temperature. 

The dipole moment of 1,10-phenanthroline was first measured by Fielding and Le Fevre,18 who obtained a moment of 4.1 D, close to the value of 3.8 D expected for the hypothetical m-2,2 -bipyridyl. Since then the dipole moments of the phenanthrolines have been studied by other groups.16,17,64 The experimental values are recorded in Table I. They were found to be in good agreement with values computed by the vector addition of the moments of the individual pyridine nuclei. The molecular polarizability of 1,10-phenanthroline has been further studied and its molar Kerr constant determined.65... 

The orientation of association of the benzene molecule about the pyrrole NH group is open to some conjecture. It was assumed from IR studies118 that the orientation was orthogonal (18). Such a model is also compatible with solvent-dependence studies of the molar Kerr constant.155 The model does not, however, adequately account for the solvent effect of benzene upon NMR chemical shifts of the a- and /3-protons of pyrrole (see Section III, B, 3, a). The NMR observations are best explained in terms of a nonplanar configuration (19) resulting not from NH-7T bonding but, instead, from a 7r-dipole interaction.151 In an attempt to confirm the orthogonal model, LeFevre et a/.155... 

With the introduction of a(—to to) the effective molar Kerr constant of pure liquids can be written as... 

Much of the careful laboratory work was performed by Tideman, such as that which led to the validation of the molar Kerr constant as a numerical criterion for the discrimination between often closely related molecular configurations.46 Tideman s son, Ian, was bom in 1938 and shortly afterwards, Tideman became a Demonstrator in Chemistry at UCL and also taught chemistry at Queen s College, Harley Street (see Chap. 4). She had a second child, Nicolette, in 1940. As a result of Tideman s research contributions at UCL, she was awarded a D.Sc. (London) in 1960. 

It is costumary to refer to as the experimentally measured Kerr constant , in spite of the fact that 5a is in general not constant but depends on the wavelength A of the analysing light, the structure and thermodynamic state of the medium, and (as is the case in macromolecular substances) the applied field strength. -In conformity with (160), the molar refraction too is a fimction of the static field ... 

Inserted into equation (166), they yield the following molar Kerr constant ... 

For a function of the form (169a), the perturbed statistical averaging of (166a) reduces to an isotropic averaging of products of unit vectors as given by formulae (104)—(107). Finally, we obtain the following molar Kerr constant ... 

Statistical averaging of the right-hand term of (174) with the distribution function (176) leads to the following molar Kerr constant, accounting for statistical-angular correlations ... 

It thus is seen to express the contribution to the dipolar part of the Kerr constant from ternary correlations. Like the parameter (152) occurring in molar refraction, it is positive or negative according to the model of orientational near-range ordering. 

In the expressions (184) and (184b) the second, temperature-dependent term defines the Born effect due to superposition of the two non-linear processes of second-order distortion and reorientation of permanent dipole moments in the electric field. Buckingham et al. determined nonlinear polarizabflities If and c for numerous molecules by Kerr effect measurements in gases as a function of temperature and pressure. It is here convenient to use the virial expansion of the molar Kerr constant, when the first and second virial coefficients Ak and Bk result immediately from equations (177), (178), and (184). Meeten et al. determined nonlinear molecular polarizabilities by measuring K in liquids as a function of temperature. 

In a first approximation, equation (190) is reducible to fluctuations in the number of molecules <(A1Va) > which are the source of light scattering. The anisotropic changes in the permittivity tensor Aeg due to statistical processes define the molar Kerr constant ... 

Values of molar Kerr constants and dipole moments of nitrogen azoles and their complexes with phenols have been obtained. " These complexes are formed by an intermolecular hydrogen bond between the pyridine-type nitrogen of the azole and the phenolic proton. " The use of dipole moments in conformational studies has shown that A-aryl- and C-aryl- and A-furyl- and C-furyl imidazoles (and benzimidazoles) are nonplanar, but l-(a-furyl)-4,5-diphenylimidazoles do have a planar bicyclic fragment. The dipole moments and conformations of azolides (A-acylazoles) have been studied. In the 1-arylimidazoles the dipole is toward the aryl group. In 4,5-di-t-butylimidazole the molecule is essentially planar, but the C-4—C-5 bond is slightly stretched. Among other imidazole derivatives which have been studied by X-ray are histidine hydrochloride, 4-acetyl-amino - 2 - bromo - 5 - isopropyl -1 - methylimidazole, 4- acetyl - 5 - methyl - 2 -phenylimidazole, and imidazole-4-acetic acid hydrochloride. 

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