Optical centers, interaction with transfer

In this section we will first consider the configurational coordinate diagram 4,7) that describes the interaction of an optical center with its surroundings in the absence of center-center interaction. Later we will deal with the interaction between two centers that results in energy transfer (4,8). 

The above described methodologies have allowed us to conduct spectroscopic studies with a finesse which is not easily attainable using conventional techniques. These laser based techniques in some combination or variation have provided us with the means to resolve or to deconvolute intrinsic features connected with the energy level structure of the systems of interest. These features have so far been assumed to remain static as a function of time. This is, of course, not always the case as various interactions of centers with their environs produce dynamical changes in the excited state and lead to relaxation, optical energy dissipation and transfer. These processes are not generally radiative. 

Johnson rearrangement of allylic alccdiols (274) and (277) led to the enantiomeric 7,8-unsaturated esters (276) and (279), respectively (Scheme 48). Both transition states (275) and (278) favor a pseudo-equatorial position of the benzyloxymethylene substituent the newly formed chiral center is obtained in very hi optical purity throu the chirality transfer process. As a consequence of this geometrical preference, secondary allylic alcohols invariably provide predominantly ( )-configured double bonds upon thermal Gaisen rearrangement The ( -selectivity usually increases with the steric bulk of the C-2 substituent, an effect which was rationalized by a pseudo-1,3-diaxial interaction in the transition state leading to the (Z)-alkene (280 Figure S). ... 

---