Through bond mechanism

If the spin-spin information was being transmitted by the normal through-bond mechanism the upfield three proton signal would be expected to occur as a doublet because these protons are the only ones which can assume the required planar zig-zag conformation 77>78h Preliminary results, using the change in chemical shift method 79>, indicates that the energy barrier to rotation is of the order of 20 k.cal.mole O. As expected the silicon compound (39) shows a nine proton doublet... 

Just why TB-mediated EET takes place so rapidly in 27(10) is currently a mystery, but this example certainly underscores the importance of the through-bond mechanism in mediating not only ET but also EET processes. 

In the same way, the displacement of the unpaired electron over the whole molecules was observed for (d) and (e) cation radicals from Scheme 1-13, in which 1,4-dimethoxy-naphthalene units are syn- or anti-annelated to [2.2]paracyclophane. Taken together, the experimental results considered provide direct evidence for the through-bond mechanism of electron transfer in these paracyclophane systems. In a recent study, the electron transfer between 1,4-dimethoxybenzene and 7,7-dicyanobenzoquinone methide moieties in syn-or anh -cyclophane systems reached the same conclusion The through-bond mechanism... 

Fig. 10 Orbital description of the McConnell superexchange (through-bond) mechanism applied to a system comprising a donor and an acceptor covalently linked to a pentamethylene chain. The donor and acceptor chromophores each contribute a single tt orbital to the interaction and each C-C bridge bond is assumed to contribute a single a or a MO, depicted as the former type in the figure. T is the interaction matrix element between a chromophore tt MO and the ally lie C-C a MO, and t is the interaction matrix element between two geminal C-C a MOs.

The observed shifts did not obey the McConnell-Robertson equation. It has been found from 13C NMR that a contact (through-bond) mechanism was found to be significant in... 

Figure 7. Orbital description of the superexchange (through-bond) mechanism. T is the interaction matrix element between the n orbital and the C-C a orbital and t is the interaction matrix element between two geminal C-C a orbitals.

In the species containing two phenyl units as spacer (6) the high energy transfer rate constant is indicative of a Dexter through-bond mechanism. The interposition of a saturated group like bicyclo[2.2.2]octane (bco) between the two phenyls (7)... 

The radical cation of (163) can be formed by electron transfer photochemistry and in methanol addition products are formed. A study of the photochemical reactivity of some novel 3-phenylnorbomadienes has been reported. Bichromo-phoric norbomadiene derivatives have also been synthesized and studied photo-chemically. A study of the photoisomerization of some norbomadienes has been carried out within the constrained environment of P-cyclodextrin. The bichromophoric system (164) undergoes intramolecular electron transfer by a through-bond mechanism on irradiation. The transfer is from the benzidine... 

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