Rotating polarizer

The molecular beam and laser teclmiques described in this section, especially in combination with theoretical treatments using accurate PESs and a quantum mechanical description of the collisional event, have revealed considerable detail about the dynamics of chemical reactions. Several aspects of reactive scattering are currently drawing special attention. The measurement of vector correlations, for example as described in section B2.3.3.5. continue to be of particular interest, especially the interplay between the product angular distribution and rotational polarization. 

Once again, the potential energy is inversely proportional to the sixth power of the separation. Notice that the potential energies of the dipole-dipole interaction of rotating polar molecules in the gas phase, the London interaction, and the dipole-induced-dipole interaction all have the form... 

Would you expect the energy of interaction of two rotating polar molecules, as given by Eq. 4, to depend on the temperature If so, should the interaction increase or decrease as the temperature is raised ... 

Substance between polarizer and analyzer is optically active -Analyzer has been rotated to the left (from observer s point or view) to permit rotated polarized light ihrough (substance Observer wlevorotatory). 

The induced dipole moment in a given direction fluctuates at double the rotational frequency of the molecule as shown schematically below. The upper diagram shows the electric field in phase with a rotating polar molecule. 

Differentiation of compounds by their ability to rotate polarized lights in different directions. 

Compounds can be labelled according to the direction in which a molecule of the substance will rotate polarized light. Abbreviated to either d- and /-or + and —. 

Circular Dichroism This method is used to determine the enantiomers in racemic mixtures. The isomers rotate polarized light in different directions depending on their chiral characteristics. 

Enantiomers have very similar chemical properties, but they rotate polarized light in opposite directions (optical activity, see pp. 36,58). The same applies to the enantiomers of lactic acid. The dextrorotatory L-lactic acid occurs in animal muscle and blood, while the D form produced by microorganisms is found in milk products, for example (see p.l48). The Fischer projection is often used to represent the formulas for chiral centers (cf.p. 58). 

Altar, W. Rotating Polar Groups in Organic Molecuies. J. chem. Physics... 

Both types proved to have all the chemical properties of tartaric acid, but in solution one type rotated polarized light to the left (levorotatory), the other to the right (dextrorotatory). Pasteur later described the experi ment and its interpretation ... 

RGURE 1 Pasteur separated crystals of two stereoisomers of tartaric acid and showed that solutions of the separated forms rotated polarized light to the same extent but in opposite directions. These dextrorotatory and levorotatory forms were later shown to be the (R,R) and (S,S) isomers represented here. The RS system of nomenclature is explained in the text. 

The single most important physical property that differentiates enantiomers is their ability to rotate the plane of plane polarized light. This property is called optical activity and is displayed only by chiral molecules. Thus, stereoisomers which are also chiral are known as optical isomers. Chiral molecules that rotate polarized light in a clockwise fashion are termed dextrorotatory (d) while those that rotate the beam counterclockwise are levorotatory (/). Enantiomers have optical rotations of die same magnitude but of different signs (d or /). 

CoCl2(en)2]+ are chiral, and that a chiral complex and its mirror image form a pair of enantiomers. The trans isomer is superimposable on its mirror image and does not rotate polarized light. We say that the trans isomer is an achiral complex. 

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