Polarized light, circularly plane

Enantiomers can be distinguished by their rotation of plane-polarized light at a specific wavelength, or over a range of wavelengths (optical rotatory dispersion, ORD), as well as by the difference in absorption of right and left circularly polarized light (circular dichroism. Cotton effect, CD). 

The fundamental requirement for the existence of molecular dissymmetry is that the molecule cannot possess any improper axes of rofation, the minimal interpretation of which implies additional interaction with light whose electric vectors are circularly polarized. This property manifests itself in an apparent rotation of the plane of linearly polarized light (polarimetry and optical rotatory dispersion) [1-5], or in a preferential absorption of either left- or right-circularly polarized light (circular dichroism) that can be observed in spectroscopy associated with either transitions among electronic [3-7] or vibrational states [6-8]. Optical activity has also been studied in the excited state of chiral compounds [9,10]. An overview of the instrumentation associated with these various chiroptical techniques is available [11]. 

In the discussion above, plane polarized light was described as a combination of right and left circularly polarized light. Just as a chiral medium must refract left and right circularly polarized light differently, chiral molecules must have different absorptions of the left and right circularly polarized light. Circular dichroism (CD) spectroscopy measures this differentia absorption. This technique involves the same absorption phenomenon that occurs in UV/vis spectroscopy which is discussed in Chapter 16. 

Figure 23.21 Circularly Polarized Light from Plane-Polarized Light. The circularly polarized light corresponds to the electric field vector moving In a helical pattern.

The absence of improper rotations in the symmetry point groups of chiral molecules leads to optical activity which can be observed experimentally in distinctive optical properties such as the rotation of plane-polarized light, circular dichroism, and optical rotatory dispersion. 

One of the most popular methods for detecting chirality is the measurement of the optical activity. A chiral object rotates the plane of polarization of linearly polarized light and generates ellipticity in the region of absorption bands because of the different refractive indices and absorption coefficients for left- and right-circularly polarized light - circular... 

Figure C2.15.2. Right circularly polarized light. As tire wave propagates tire resultant E sweeps out a circle in tire x-y plane.

When a material exhibits different indices of refraction for the right- and left-hand components of the circular vectors, the velocities in these directions are different and the plane of polarized light undergoes rotation. For the left- and right-hand vectors, the indices of refraction are... 

Optical Activity Certain media are optically active, which means that they interact with plane polarized light by changing the direction of polarization. A simple explanation of this effect is that optically active material interacts differently with left and right circularly polarized light respectively, for instance by exhibiting different indices of refraction with respect to these two types of polarized light. If this is the case one or the other of the circular components of plane polarized light would lag behind in that medium. 

Optical activity comes from the different refractions of right and left circularly polarized light by chiral molecules. The difference in refractive indices in a dissymmetric medium corresponds to the slowing down of one beam in relation to the other. This can cause a rotation of the plane of polarization or optical rotation. The value of specific rotation varies with wavelength of the incident polarized light. This is called optical rotatory dispersion (ORD). 

Figure 19.2 evidently shows the electric field of a plane-polarized light which consists of two components of fixed magnitude rotating in opposite directions to one another the right circularly polarized light and the... 

What is the fundamental theory of polarimetry How would you depict the plane polarized light, right circularly polarized light and left circularly polarized light diagramatically ... 

Circular dichroism (CD) S Change in rotation of plane-polarized light upon binding to measure conformational change... 

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