Equations of CD spectroscopy

In a chiral molecule the electron rearrangement during a transition is always helical which requires that p and m have a parallel component. The Rosenfeld equation for the CD intensity (or CD strength or rotational strength, R) of a transition in a collection of randomly oriented chiral molecules is (4)  

CD may sometimes be used to deduce the strxicture of a system. This is only really viable when the system can be considered as a collection of chromo-phores (spectroscopically well-defined subunits of a molecule) each of which is only slightly perturbed by the rest of the system. In the rest of this section we shall consider the coupling of two intrinsically achiral chromophores that are chirally oriented with respect to one another. A range of applications of this theory is given in (4). We have to treat eda/mdf transitions separately from 

The dependence of the different kinds of induced moments on the geometry of the system is very different, thus when we wish to extract geometric information from CD we must be aware of which situation we have. 

We choose the axis system and vectors illustrated in Rgure 8 with A in front and C behind. The x-axis lies along Rac the vector from the A origin to that of C, and z lies along the y-z projection of (i , the A chromophore edtm. We also define three angles a (0 a 180°) the angle between R c and (i , -y (0 s 7  

We shall refer to the system as being right handed if the three vectors ji and Rac (CAR) form a right-handed coordinate s tem. The angles relate to the vectors as follows (4)  

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