Polarimetry polarized light, nature

Since the early times of stereochemistry, the phenomena related to chirality ( dis-symetrie moleculaire, as originally stated by Pasteur) have been treated or referred to as enantiomericaUy pure compounds. For a long time the measurement of specific rotations has been the only tool to evaluate the enantiomer distribution of an enantioimpure sample hence the expressions optical purity and optical antipodes. The usefulness of chiral assistance (natural products, circularly polarized light, etc.) for the preparation of optically active compounds, by either resolution or asymmetric synthesis, has been recognized by Pasteur, Le Bel, and van t Hoff. The first chiral auxiliaries selected for asymmetric synthesis were alkaloids such as quinine or some terpenes. Natural products with several asymmetric centers are usually enantiopure or close to 100% ee. With the necessity to devise new routes to enantiopure compounds, many simple or complex auxiliaries have been prepared from natural products or from resolved materials. Often the authors tried to get the highest enantiomeric excess values possible for the chiral auxiliaries before using them for asymmetric reactions. When a chiral reagent or catalyst could not be prepared enantiomericaUy pure, the enantiomeric excess (ee) of the product was assumed to be a minimum value or was corrected by the ee of the chiral auxiliary. The experimental data measured by polarimetry or spectroscopic methods are conveniently expressed by enantiomeric excess and enantiomeric... 

Scanning laser polarimetry measures the change in the polarization state of an incident laser light passing through the naturally birefringent nerve fiber layer to provide indirect estimates of peripapillary nerve fiber layer thickness. 

Generally, polarimetry requires the establishment of the type, quality, azimuth and ellipticity of the polarization. In addition, polarization of some type of irradiated or dispersed light [irradiated by natural and artificial objects or some of light-source] is difficult and it can contain simultaneously linear, elliptic, circular or partial polarized components [94]. The whole polarimetric analysis of such objects needs to investigate. At the same rime, appheation of the standard polarization optical elements, for the investigation of the polarization state of each section, it is necessary to take each complete set of different gradient elements, and for this reason it is difficult and labor-intensive to carry out such investigations. 

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