Through-space electronic interactions

Note the donor group is now one carbon further apart and its influence on the nearest reaction center is in the opposite sense (polarity alternation). However, a through-space electronic interaction must be important also, as the exo isomer displays no selectivity. 

A stilbene-cored poly(glutamate) dendrimer in benzene underwent intermolecular photochemical [2 + 2] cycloaddition. The bisignate circular dichroism signal of the resulting cycloadduct indicated the formation of chiral aggregates with through-space electronic interactions between the two stilbene cores. 

X, using dissociative electron-transfer theory. A through-space stabilizing interaction (homohyperconjugation) in the 4-X-substituted bicyclo[2.2.1]heptane radical species has been shown to exist. 

This indicates that there is neither a strong through-band electronic interaction nor a through-space interaction between the fullerene moiety and the attached group [75,81,110], An exception to this is the fullerene derivatives 5 (Fig. 6) in which the UV spectrum shows two new bands at 455 and 500 nm that are not observed in the pyrene or in the pure fullerene spectra [75], Moreover, the solvent... 

Barriers to rotation and conformational states around sp2-sp3 play an important role in the determination of the steric requirement of a substituent. These barriers are predominantly composed by the difference in through-space nonbonding interactions in ground and transition states. They are typically free from electronic contributions, in contrast to the quantitative approach of steric effects, which proceeds through reaction rates or (a + n)-barriers to rotation, in which the steric part is only a perturbation of the energetic content. 

Through-space electron transfer Electron transfer for which the relevant electronic interaction between the donor and acceptor sites is mediated either by direct orbital overlap or by superexchange interaction via intervening molecular entities not covalently bound to the donor or acceptor sites. 

In actual practice the unpaired electron is not free. It is generally associated with one or more nuclei, which may have a nuclear spin magnetic moment. This moment generates a magnetic field at the location of the unpaired electron, due to the so-called contact or Fermi hyperfine interaction (the electron has a finite probability of penetrating to the atomic nucleus) and to the through-space dipolar interaction between nuclear and electronic magnetic spin moment, represented by... 

The distance dependencies of photoinduced electron transfer rates have been examined in anthracene-spacered porphyrin-quinone cyclophanes, and the same authors have also discussed the distance dependencies of photo-induced electron-transfer rates in benzene-, naphthalene-, and anthracene-spacered porphyrin-quinone cyclophanes and biphenylene-spacered porphyrin-quinone cyclophanes. Photoelectron transfer reactions of the porphyrin-quinone cyclophanes (3) and their zinc complexes have been examined, and in some cases at least interaction of the quinone carbonyl group with the zinc atom may be an alternative to through-space electron transfer. A study of intramolecular photoinduced electron transfer for the quinone-porphyrin cyclophane type (4) containing the especially strong acceptor 7,7,8,8-tetracyanoquinodimethane (TCNQ) has appeared." The distance dependence of the TCNQ and porphyrin is of particular interest, and to this end the corresponding 2,8-naphthalenediyl-TCNQ-porphyrin has been synthesised. 

---