Optical rotation general theory

The first attempt to formulate a theory of optical rotation in terms of the general equations of wave motion was made by MacCullagh17). His theory was extensively developed on the basis of Maxwell s electromagnetic theory. Kuhn 18) showed that the molecular parameters of optical rotation were elucidated in terms of molecular polarizability (J connecting the electric moment p of the molecule, the time-derivative of the magnetic radiation field //, and the magnetic moment m with the time-derivative of the electric radiation field E as follows ... 

Paul Pfeiffer discovered a very interesting stereochemical phenomenon, which now bears his name — the Pfeiffer effect this has received a good deal of attention.30 When an optically active substance which is stable in solution is added to a solution of a labile chiral substance, the optical rotation of the solution changes, reaching a new level in some hours. Several theories have been advanced to explain the phenomenon, the most satisfactory based on the supposition that the optically active ion or molecule forms an association with one isomer of the racemic pair of the labile substance and thus shifts the dextro—levo equilibrium. In general it is not possible to use this as a means of resolution, for when the added optically active substance is removed from the labile material, the latter immediately racemizes. 

The next section (Sect. 2) is devoted to a lengthy discussion of the molecular hypothesis from the point of view of quantum field theory, and this provides the basis for the subsequent discussion of optical activity. Having used linear response theory to establish the equations for optical activity (Sect. 3), we pause to discuss the properties of the wavefunctions of optically active isomers in relation to the space inversion operator (Sect. 4), before indicating how the general optical activity equations can be related to the usual Rosenfeld equation for the optical rotation in a chiral molecule. Finally (Sect. 5), there are critical remarks about what can currently be said in the microscopic quantum-mechanical theory of optical activity based on some approximate models of the field theory. 

It has been shown that the main medianism responsible for EB in solutions of rigid-chain polymers is the rotation of their polar molecules as a whole whereas the anisotropy of the dielectric polarizability of the macromolecules only provides a small contribution to the Kerr effect. Hence, the general theory of the Kerr effect for rigid dipole particles with axial symmetry of the optical polarizability can be... 

It should be mentioned that there is still no general quantitative theory for these problems, and therefore we can usually only apply empirical knowledge and analogies. A few typical examples will serve to illustrate various types of interaction (e.g. salt formation, inclusion compounds and associates), and their influence on optical rotation and dichroic absorption will be discussed together with the conclusions drawn from this. 

It was easy to see that in an octahedral structure four different compounds could be made with a central metal atom with two each of three different substituents. This compound would have the general formula MA2B2C2. Different compounds that could be formed with identical formula are called isomers. It was also easy to see that two of the six possible isomers were chiral. All of the possible isomers of octahedral MA2B2C2 are drawn in Figure 1.15. The solid lines in this figure represent the bonds from the central metal atom to the substituents, and the dashed lines have been added to show the outline of the octahedron, which contains eight triangular faces. A real proof of the coordination theory of Werner was the successful measurement of optical rotation in octahedral complexes in 1911 [3]. 

This electro-optical effect, commonly observed as transient changes in optical birefringence of a solution following application, removal, or reversal of a biasing electric field E(t), has been used extensively as a probe of dynamics of blopolymer solutions, notably by O Konski, and is a valuable tool because it gives information different in form, but related to, results from conventional dielectric relaxation measurements. The state of the subject to 1975 has been comprehensively presented in two review volumes edited by O Konski (25). The discussion here is confined to an outline of a response theory treatment, to be published in more detail elsewhere, of the quadratic effect. The results are more general than earlier ones obtained from rotational diffusion models and should be a useful basis for further theoretical and experimental developments. 

Liquid crystals are generally characterized by the strong correlation between molecules, which respond cooperatively to external perturbations. That strong molecular reorientation (or director reorientation) can be easily induced by a static electric or magnetic field is a well-known phenomenon. The same effect induced by optical fields was, however, only studied recently. " Unusually large nonlinear optical effects based on the optical-field-induced molecular reorientation have been observed in nematic liquid-crystal films under the illumination of one or more cw laser beams. In these cases, both the static and dynamical properties of this field-induced molecular motion are found to obey the Ericksen-Leslie continuum theory, which describe the collective molecular reorientation by the rotation of a director (average molecular orientation). 

No theory has been published for this case. It can be expected, from general considerations, that the electrohydrodynamic processes will result in a change in the optical properties of the layer of the Sc phase, even when there is no change in the arrangement of the smectic layers, since the director has an extra degree of freedom—the possibility of rotation around the normal to the layers. Electrohydrodynamic instabilities in the 5c phase have been repeatedly observed in experiment. The formation of domains in smectic C under the influence of an electric voltage was first observed [127] with p-n-heptyloxybenzoic acid (HOBA) ... 

Although much of the book focuses on physical theory, 1 have emphasized aspects of optical spectroscopy that are especially pertinent to molecular biophysics, and 1 have drawn most of the examples from this area. The book therefore covers topics that receive little attention in most general books on molecular spectroscopy, including exciton interactions, resonance energy transfer, single molecule spectroscopy, high-resolution fluorescence microscopy, femtosecond pump-probe spectroscopy, and photon echoes. It says less than is customary about atomic spectroscopy and about rotational and vibrational spectroscopy of... 

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