Symmetry of Halonium Complexes in Solution

摘要: In this thesis the symmetry of two interaction types involving electropositive halogens have been studied in solution; NXN halogen bond (X = Br or I), and CXC previously characterised, cyclic, 1,2-bridged halonium ions Cl Br), respectively. The three model structures included are bispyridine, 1,2-bis(pyridine-2-ylethynyl)benzene 1,2-bis((4-methylpyridin-2-yl)ethynyl)benzene triflate complexes. Model representing dimethylethyleneand ethylenehalonium ions. All comprised symmetrically arranged atoms, but possibility to exist as either a static, symmetric structure, asymmetric, fast equilibrating tautomers. For positive is positioned with equal distances electron donor nitrogens/carbons. asymmetric structures, always closer one nitrogens/carbons, consistently jumping between investigation NMR spectroscopic method Isotopic Perturbation Equilibrium (IPE) has applied for distinguishing single structure from rapidly, interconverting technique measures C isotope shifts, obs, resulting unsymmetrical introduction deuterium isotopes molecule which doubt. Based on magnitudes, signs, temperature-dependency obs obtained spectra mixture non-labelled labelled molecules, being considered can be determined. IPE experiments revealed that all bis(pyridine)based complexes were best represented dichloromethane. arrangement was also shown independent environmental factors, such increased solvent polarity tight binding counter ion. Thus, these observations indicated formation energetically favourable. N chemical shifts pyridine rings significantly stronger iodonium than corresponding bromonium complexes, suggesting covalent character NIN an ionic NBrN interaction. Strongest observed bispyridine NN freely adjustable provide most favourable Ionisation 2,3-dihalobutane 1,2-dihaloethane precursors SbF5-SO2 at -80 C attempted generation desired Both characterised structures; dimethylethylenebromonium their values, ethylenebromonium ion dynamic behaviour, typical slow equilibrium, signals its H spectra. spectral pattern ethylenechloronium consistent equilibrium. dimethylethylenechloronium could not determined, they, if formed all, immediately rearranged. SO2 sufficiently nucleophilic add cations formed. Hence, source asymmetry ascribed labile addition cyclic open -halocarbenium __________________________________________________________________________________________