No-bond resonance system

The distances measured show clearly that here is a no bond resonance system extended to five sulfur atoms. 

Finally some compounds related to the thiathiophthene no-bond resonance system may be regarded as containing contributions from isothiazolium forms (8 <-> 9).146... 

Resins s. Ion exchange resins Resolution s. Stereoisomers Resonance system s. No-bond resonance system Resorcinol monoesters s. m-Diol monoesters Resorcinols... 

Replacement of oxygen by sulfur Thiothiophthene no-bond resonance system... 

If we now consider the a and it bondings, formula 82 for both resonance structures has twelve or ten it electrons according to whether or not we admit that every sulfur atom retains only two unshared electrons on the M level. So the no bond resonance does not show the existence of a naphthalene-like 107r-eleetron system. If dotted lines are used to represent half bonds, the system con-... 

As it were a two dimensional extension of the no-bond-resonance concept has been synthesized in XVI The structure of this compound has been described as a sulfur analogue of coronene 8) since it comprises a24 ji-electron system. 

In Chapter III.3. the model compounds IX—XI, XIII and XVI were discussed as examples of the extension of the no-bond resonance concept. Derivatives of these model systems have been synthesized 4,8,81,112-119) (gee Scheme 2) and... 

It is expected that hyperconjugation would be enhanced in certain systems containing heteroatoms. If one atom with an unshared electron pair is a particularly good electron donor and another a good cr acceptor, the u contribution should be enhanced. This is represented by a charged, no-bond resonance structure. 

We assert in this review that, at this point in time, there are several examples of neutral molecules which have been shown to display either bond or no-bond homoaromaticity. These include, in addition to the boranes mentioned above in Section III. B, cyclohepta-triene, norcaradiene, bridged cycloheptatrienes and norcaradienes, semibullvalenes, bar-baralanes, bridged annulenes, etc. Confirmation of the homoaromatic character of these systems comes from thermochemical and spectroscopic studies, and force field and ab initio calculations. In particular, the work of Roth and coworkers must be mentioned in this connection in that they were the first to provide reliable resonance energies of a large number of these neutral molecules225 226. These authors have also demonstrated that systems such as bicyclo[2.1.0]pentene are homoantiaromatic. 

Other alloy systems in which ESR has been an effective experimental tool include silicon nitride (Shimizu et ai, 1982b Ishii et ai, 1982c), silicon oxide (Holzenkampfer et a/., 1979 Shimizu era/., 1980a Dvurechenskii et al., 1982a), and silicon oxynitride (Kubler et ai, 1983). In the silicon nitride system the N hyperfine interaction provides an additional contribution to the observed -values and linewidths, which indicates that the spins on the silicon atoms are influenced by nearby nitrogen atoms. This situation contrasts with that observed in a-Si H or a-Si F in which no strong influence of the H or F atoms on the Si dangling bond resonance is observed (Ishii et ai. 

---