NMR study of the dynamic behaviour of the system 2-ethylhexylsodium-2-ethylhexyllithium in heptane

Mixtures of 2-ethylhexylsodium and 2-ethylhexyllithium are studied by H-1- and C-13-NMR spectroscopy in the temperature range from 20 to - 50 degrees C in hydrocarbon solutions. Characteristic temperature-dependent spectra ob tained are indicative of dynamic exchange processes taking place in the sys tem. The following activation parameters are found: Delta H-not equal = 31. 7 +/- 2.7 kJ mol(-1); Delta G(313)(not equal) = 58.7 +/- 0.6 kJ mol(-1); De lta S-not equal = - 86.37 +/- 10.8 J mol(-1) K-1. The negative value of the activation entropy indicates that the exchange proceeds through the associ ative mechanism. The participation in exchange reactions of aggregates, con taining both sodium and lithium derivatives, is suggested. (C) 1999 Elsevie r Science S.A. All rights reserved.