Jozef Hodyl PhD Thesis - Theses - Flinders University

it should be borne in mind that previous comparisons of solution 13 C NMR arisingfrom guest anions and host guest complexes of this type have always revealed almostnegligible chemical shift perturbation for the host carbon atom resonances, butusually some quite significant perturbation to the chemical shift values of the guestresonances. Proceeding on this basis it is then reasonable to postulate that the newresonance in spectrum D (compared to C) at 182.2 ppm is from C1 of the guest(183.0 ppm in B), the new resonance at 167.9 ppm is from C3 (166.7 ppm in B), thenew shoulder at 138.0 ppm is from C5 (139.7 ppm in B) and the new broadresonance at 110.2 is from a merging of C4 and C2 (113.0 and 108.3 ppm in B).Thus there seems little doubt that not only is 2,6-dihydroxybenzoate present in thesample used to produce spectrum D, but that the altered chemical shift values for theguest indicate a more intimate association than just a physical mixture of the twospecies.The preceding spectra are for a host-guest combination where the very highestuptake of the guest occurred (95%) so examination of the solid state NMR spectrafrom a lower percentage uptake combination is also illustrative as a basis forcomparison. The guest species, m-methoxybenzoate, with 55% inclusion in Si-GPS-[Cd(Trac)](ClO 4 ) 2 , 94, was chosen for this purpose.The acquired spectra aredepicted in Figure 6.8.Spectrum A, for m-methoxybenzoate, shows splitting of all of the singleresonances found in the solution spectrum. This spectrum when viewed incombination with spectrum B does display evidence for inclusion of m-methoxybenzoate in Si-GPS-[Cd(Trac)](ClO 4 ) 2 , 94, as depicted in spectrum C, withsome bands for this guest molecule clearly visible, particularly C1 which movesfrom 183.0 ppm in A to 184.1 ppm in C.115