7t*LUMO

Also, the bonds between the polyene and the cyclopropyl ring are shortened due to bonding primary overlap between % of cyclopropyl and 7t(LUMO) of the polyene. 

If the antibonding Walsh MO is involved in the two-electron stabilizing interactions (bicyclo[2.1. Ojpentene and bicyclo[3.1. Ojhexenyl cation, Figure 11), then charge transfer to 7t(LUMO) of the polyene will lead to... 

A quite simple picture is obtained in the ET case if we go from many-particle theory to orbitals via Koopmans theorem. This treatment is correct in the limit case when donor and acceptor exchange electrons using well-separated MO s on donor and acceptor. The simplest example is the case studied by McConnell [7] (fig.l). Two identical n systems are connected via a hydrocarbon chain, which acts as a bridge. ET is possible in an open shell system. We may assume that either the whole ET system is either a negative ion or a positive ion and that the corresponding neutral molecule has closed shells. In the former case the electron occupies 7t LUMO. In the latter case there is a hole in rt HOMO. 

The AAfff, 7T-HOMO and 7T-LUMO energy and // of phenothiazine [21] and benzo[a]phenothiazines [22-29] are summarized in Table 7. 

Electron-rich S-N heterocycles usually exhibit intense colors ranging from yellow to orange and red to blue. The colors are due to low-energy (n jt or n jt ) transitions. For example, the Stt-electron heterocycles R2PN3S2 (16) and S3N3O2 (17) both have intense purple colors due to a visible absorption band at 550 560 mn attributed to the HOMO(7t ) LUMO(7t ) ttansition. 

Figure 7.7 (a) The 7t LUMO and major contributing orbitals of computational... 

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