Infrared Multiphoton and Collision Induced Dissociation Studies of Some Gaseous Alkylamine Ions

Collision induced dissociation and infrared multiphoton dissociation of ions formed in di- and triethylamine, di- and tri-n-propylamine, and diisopropylamine were investigated by Fourier transform ion cyclotron resonance mass spectrometry. Molecular ions of all amines except di-n-propylamine produced similar fragment ions when subjected to either dissociation technique. The initial fragmentation involved C(alpha)-C(beta) bond cleavage, loss of an alkyl radical, and formation of an immonium ion. Subsequent fragmentations of the immonium ions produced by both dissociation mechanisms involved McLafferty type rearrangements and loss of alkenes. The molecular ion of di-n-propylamine fragmented by a different mechanism when subjected to infrared irradiation. Protonated molecules of di- and tri-n-propylamine yielded C3H6 and an ammonium ion upon infrared multiphoton dissociation, while protonated molecules of the other amines did not dissociate using this technique. Collision induced dissociation, on the other hand, produced fragmentation for all protonated molecules. Explanation of the different fragmentations observed for the two dissociation techniques is given in terms of a mechanism involving a tight transition state for protonated di- and tri-n-propylamine dissociation. Keywords: Infrared Multiphoton Dissociation; Collision Induced Dissociation; Alkylamines; Fourier Transform Ion Cyclotron Resonance Mass Spectrometry.