A Study of Cation-exchange Reactions in the System Potassium Durosemiquinone – Potassium Tetraphenylboride – Tetrahydrofuran

Abstract

The electron spin resonance (e.s.r.) spectrum of potassium durosemiquinone in tetrahydrofuran has been studied as a function of temperature and found to exhibit line-width alternation indicating the presence of an intramolecular migration of the potassium ion between the oxygens of the semiquinone. The addition of potassium tetraphenylboride to the system produces intermolecular scrambling of potassium, the spectral effects of which are superimposed upon those of the intramolecular exchange. From the spectral line-shapes approximate values of the activation energies and frequency factors were derived. The tetraphenylboride anion did not play a detectable role in the various exchange mechanisms.On a CtudiC le spectre r.p.e. du sel de potassium de la durosemiquinoneenfonction de la tempkrature et on a trouvC qu'ils prCsentent une alternation des largeurs de raie qui indiquerait que I'ion de potassium effectue des migrations intramolCculaires entre les divers atomes d'oxyg6ne de la semiquinone. L'addition de tCtraphCnylborure de potassium au systtme a comme effet de permettre une permutation des ions potassium entre les molCcules; ces migrations provoquent des changements spectraux qui se superposent a ceux provoquCes par les Cchanges intramolCculaires. A partir des formes des bandes dans les spectres, on a pu domer les energies d'activation et les facteurs de frCquence de ces rCactions. I1 ne semble pas que I'anion tCtraphCnylborure joue un rBle dttectable dans les divers mCcanismes d'Cchange.

Equilibrium studies by electron spin resonance. X. Thermodynamics of ion-pair dissociation by the use of time-averaged coupling constants

“…A similar effect has been observed for the benzoquinone anion radical in HMPA saturated with KI3 *5and for durosemiquinone in tetrahydrofuran. 15 The approach of the sodium ion to the carbonyl sandwiched between the two tertbutyl groups is not as sterically hindered as it is for the potassium ion due to the smaller size of the sodium cation. From this argument we would expect the addition of Lil to the free ion in HMPA to result also in the observation of an asymmetric esr spectrum.…”