Homocyclic Systems

The one-electron oxidation of homocyclic inorganic ring systems is expected to produce the corresponding cation radicals. An effective reagent for this process is 

The oxidation of cyclo-Sg with strong oxidising agents, e.g. AsFs, produces polysulfur cations, which are isolated as lattice-stabilised salts of dications, e.g. 

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Homocyclic Systems. Cyclobutanediyls exhibit spin states that are very close in energy. The triplet state is preferred by only l.Vkcal mol it can be observed by EPR spectroscopy because the ring closure to a bicyclo[l. 1. Ojbutane is spin-forbidden. Singlet cyclobutanediyls are predicted as very short-lived transition states for the ring inversion of bicyclo[1.1.0]butanes (AF 50kcal mol ). Quantum chemical calculations predict that the heavier group 14... 

This section begins with an account of large homocyclic systems, i.e. those in which only one p-block element is present. These rings are exclusively saturated systems, i.e. they involve single bonds between the p-block elements. By contrast, the subsequent discussion of heterocyclic systems includes both saturated and unsaturated rings. The latter involve some form of multiple bonding between different p-block elements. 

The difference in stability noted above is of the same order of magnitude as that found for the formation of adducts 22 and 23 for the reaction of 1,3,5-trinitrobenzene with the OH" and MeO" ions, respectively. Examination of the activation parameters shows some relevant differences between the heterocyclic and the homocyclic systems, however. The higher reverse rate for the methoxy adduct of trinitrobenzene 23 relative to the corresponding hydroxy adduct 22 is controlled by the higher activation entropy, whereas the higher reverse rate for the methoxy adduct of the dinitropyridine 1 relative to 3 is determined by the activation enthalpy. The entropy effect has been related to the different role of intramolecular interactions of the hydroxy adducts in the benzene and pyridine series. The reason for this difference is still unclear, however.45... 

Homocyclic Systems.— The photo-initiated cycloaddition of benzenes and alk-ynes continues to be a route of choice for cyclo-octatetraenes (cot s). Thus while hexafluorobenzene and various phenylacetylenes photo-add, giving the cot s (3) and (4) by thermal reorganisation of the isolable bicyclic intermediate (2), ... 

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