Orthogonal activation modes

In carbohydrate chemistry fluorodesulfuration has become a convenient tool for switching between different, orthogonal modes of glycosidic activation [158] (Scheme 2.70). 

Fig. 3 The three most common modes to activate linear Ugi-products for cyclization, especially if the cyclization involves Ugi-reactive groups (e.g., acid, oxo-compound, or amine). Activation is mostly achieved with convertible isonitriles, i.e., activated amides (see text). Other MCRs follow similar concepts. With orthogonal second functionalities for cyclizations such deprotection and/or activation is not required (see below, e.g., RCM or cycloadditions)...

Fig. 40 Thermal hole transfer processes in bismethyleneadamantane radical cation, 41, and bismethylenebishomocubane radical cation, 42 the former process is formally symmetry-forbidden, because the two active 77 MOs are orthogonal to each other, whereas the latter is symmetry-alio wed, because the two active 77 MOs lie in the same plane. The inset, 43, depicts the major symmetry-breaking vibration, a torsional mode, which facilitates HT in 41.

In the subsequent spin-coupled calculations [9], the < > were optimized as linear combinations of all the LMOs which correspond to X—Y bonds, plus all the virtual orbitals. This scheme is entirely equivalent to expanding the in the full basis atomic basis set, except that it maintains the orthogonality between the active orbitals and the inactive space, which consists of all the other doubly-occupied MOs. The spin function 0 was fully optimized in the full spin space. The active orbitals were thus fully optimized without constraints on their form, on the degree of localization, on the overlaps between them, or on the mode of coupling the electron spins. Nevertheless, we found for each molecule that the optimized spin-coupled orbitals consist of pairs, each clearly associated with a particular two-centre bond, and with predominantly singlet coupling of the electron spins. For example, we show in Figure 2 the pair of spin-coupled... 

We examined the effect of coupling between surface plasmon polariton (SPP) modes on the optical activity of metal nanostructures. By measuring the in-plane wave vector dependence on transmission and polarization azimuth rotation, we show that coupling of the SPP modes with orthogonal polarization localized at different interfaces is responsible for the optical activity in metal nanostructures. 

---