EFFECTS OF FUNCTIONAL-GROUP INTERACTIONS ON THE DISSOCIATION REACTIONS OF PROTONATED AMINO-ALCOHOLS

The dissociation reactions of protonated amino alcohols were examined in a quadrupole ion trap mass spectrometer. Multi-stage collision-indu ced dissociation techniques were used to characterize the ions and the ir fragments and to assist in the determination of the dissociation me chanisms. In addition, semi-empirical calculations were used to ration alize the results on the basis of the thermodynamics of the reactions in question. The reaction of special interest was the double eliminati on of water and ammonia. For this high-energy process, it is shown tha t the initial deamination step is the thermodynamically favored one in most cases. The enthalpies of formation for the various precursor and product ions and also those for some of the reaction intermediates we re estimated using molecular modelling and semi-empirical calculation methods. The values obtained indicated that the minimum endothermicity of the sequential deamination-dehydration reaction ranges from 209 to 460 kJ mol-1 for the compounds studied here. Moreover, protonation at the amine site was found to be energetically favored by 38-192 kJ mol -1 over protonation at the hydroxyl site.