E-7r conjugation

The above analysis illustrates why it is helpful to consider the enediyne moiety as two independent re-systems. As discussed above, the conjugated out-of-plane 7r-system of the reactant is smoothly transformed into the conjugate 7r-system of the product (e.g., the aromatic system of benzene) without an overall change in the number of bonds. We will refer to this group of electrons as out-of-plane MOs or simply as the re-system . In contrast, the two in-plane re-bonds are transformed in a more drastic way to the new cr-bond and a pair of radical centers. We will refer to this system of orbitals as in-plane re-bonds or as the a system . 

Molar absorptivity is a physical constant characteristic of the particular substance being observed and thus characteristic of the particular 7r electron system in the molecule. Typical values for conjugated dienes are in the range e = 10,000 to 25,000. Note that the units are usually dropped. 

Contrary to fraras-azoferrocene, the cis form exhibits one-step 2e oxidation waves, and its oxidation potential, E° = 0.03 V in Bu4NC104-benzonitrile, is more negative than that of the trans form (E() = 0.29 and 0.50 V vs. Ag/Ag ) by 0.3 V. These data imply that the 7r-conjugation ability and electron-withdrawing nature of the azo group is retarded in the cis form. 

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