Electron spin resonance study of the 1 : 1 hydrogen-bonded complex of di-t-butylnitroxide with methanol. An analysis of an acceptor : self-associated donor equilibrium

Abstract

The formation constant Kf for the 1:1 complex of di-t-butylnitroxide with methanol has been determined over the temperature range –23°C to + 65°C by measuring the variation of aN with methanol concentration. The solvent was carbon tetrachloride. The Newton–Raphson (N.R.) method was used in treating the results. Proper account was taken of the self-associated nature of the methanol. With suitable modifications the analysis should be applicable to other spectroscopic techniques used to study complex formation between two species, one of which is self-associated. Evidence has been obtained which favours the existence of linear rather than cyclic tetramers of methanol in equilibrium with monomers. The enthalpy of formation of the hydrogen-bonded complex was low, namely –6.7 ± 1.8 kJ mol–1. The temperature coefficients of aN in the free and complexed nitroxide are of opposite sign. For the complex, this is shown to be the consequence of proton hopping in an asymmetric double-minimum potential with an energy difference between the minima of 9.4 ± 0.8 kJ mol–1.