PUB - Publikationen an der Universität Bielefeld

The gas phase basicity (GB) and proton affinity (PA) of propionamide were determined by the following four different methods using FT-ICR spectrometry and tandem mass spectrometry: (i) observation of the proton transfer equilibrium and determination of the equilibrium constant K by FT-ICR; (ii) determination of the rate constants for proton transfer to and from propionamide by FT-ICR for an indirect determination of K; (iii) the ''bracketing method'' by measuring the efficiency of deprotonation of protonated propionamide by a series of reference bases by FT-ICR; and (iv) the ''kinetic method'' by observing the dissociation of proton bound heterodimers of propionamide either as metastable ions (MIKE technique) or by CID with a tandem mass spectrometer. The average values obtained by the four methods are GB(propionamide)=844.9+/-4.1 kJ mol(-1) and PA(propionamide)=873.0+/-1.5 kJ mol(-1). The results of all methods show good consistency with a maximal deviation of +/- 6 kJ mol(-1). Although the ''bracketing method'' and the ''kinetic method'' were not applied under ideal conditions the GB and PA values obtained are in reasonable agreement with those from the other methods, showing that the ''nonequilibrium'' methods can be reliably used for GB and PA determination of aliphatic carboxamides. (C) 1997 Elsevier Science B.V.