Konformationsuntersuchungen durch Elektronenspinresonanz Two-Jump-prozesse in Benzyl-phosphonium Salzen / Conformation Studies by Electron Spin Resonance Two-Jump Process in Benzyl-phosphonium Salts

The ESR spectra of 4-oxyl-benzyl-phosphonium-bromide radicals show a temperature dependence of the methylene protons and the phosphorus nucleus coupling constants which is explained by a hindered rotation of the phenoxyl ring of the radicals. Furthermore compounds with different phosphor substituents exhibit the phenomenon of a two jump process. This effect is described by an isomerisation of two symmetric radical conformations. Activation energies for this process are found to be around 7 kcal/Mol. The conformation of the radicals can be discussed as staggered ethane analogues. A lower limit value for the hyperconjugation Bᴾ -parameter is proposed.