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The macrocyclic ring interconversion of four maleonitrile mixed oxadithia crown ethers of variable ring size, mn-12-S2O2, mn-15-S2O3, mn-18-S2O4 and fn-12-S2O2, were studied by 1H and 13C NMR spectroscopy and by molecular modelling. The barriers to ring interconversion were estimated using variable temperature NMR spectroscopy and from the calculated activation energies, together with the spin-lattice relaxation times of the CH2 carbon atoms, conclusions were drawn regarding the intramolecular flexibility of the crown ethers in both the free state as well as the complexed state incorporating either AgI, BiIII, SbIII, PdII or PtII metal cations. Furthermore, both the stoichiometry of the complexes and the coordination sites of the crown ethers to the various cations were also clearly implicated. Molecular modelling was also utilised to ascertain the preferred conformers of the four compounds and their corresponding complexes, the results of which corroborated the experimental NMR results to a high degree.
A report of Mikhail Gasparov's 1989 book on the 'History of European Versification' is the starting point of the discussion in this article of the types of versification found in the Insular Celtic literatures from their first documenation in the early middle ages to the present day, as Gasparov's survey does not cover these poetries. It is claimed here that their metrical constraints were pre-literate and first and foremost geared at aural reception. The introduction of writing led to an increase in metrical sophistication which, while still basically oral, because of the process of "prelecting" (i.e. reading out aloud to illiterate or semi-literate audiences), required a very careful appreciation of their metrical skills. Contact with English and French syllabic poetry in the later middle ages and particularly in the modern period produced so-called "free verse" poetry. The word "free" in this particular context meant that the rather loose metrical constraints of these majority literatures in no way compared with the extraordinarily high metrical sophistication of the native oral derived or "bardic" poetry.