Fragmentation of even electron ions: Protonated amines and esters

Abstract

The fragmentation of protonated amines and esters is examined by collision induced dissociation of mass selected ions generated by chemical ionization. Four fragmentation types are observed: (i) loss of an alkane moiety, explicable in terms of a four-centered reaction, (i) loss of alkene, also explicable as a four-centered process, (iii) loss of an alkyl radical, requiring electron unpairing, (iv) losses of other neutral molecules, viz. acids and alcohols from protonated esters, or amines and ammonia from protonated amines. Proposed mechanisms were checked by characterizing selected product ions through their collision induced dissociation spectra. The usefulness of these generalizations is substantiated by the successful prediction of the fragmentation patterns and the order of relative abundances of daughter ions for eight unknowns including some containing functional groups not studied previously.

An energy-resolved study of the fragmentation reactions of alkyl ammonium ions

“…[3]) is analogous to the elimination of C,H,, for the tetrapropyl ammonium ion. The (C4H9),NCH,+ (mlz 142) ion formed in reaction [3] has been shown (19) to fragment further by elimination of propene (reaction [4]) 141 (C4H9),NCH?+ + (C,H,)CH,NCH,+ (mlz 100) + C,H, and, in agreement, we see mlz 100 as a significant product at higher collision energies. Rolando and co-workers (10) have provided evidence that C4Hg+ is a secondary fragmentation product rather than a primary product for the tetrabutyl ammonium ion; the results of Fig.…”

“…These results have been rationalized (2) in terms of a fragmentation mechanism involving the initial formation of a [R,+---NH(R,),] ionldipole complex which either may separate to form R1+ (accompanied by H-migration to form a secondary o r tertiary carbenium ion) or may undergo internal proton transfer resulting in olefin elimination and formation of a protonated amine. The alkyl ion and protonated amine products also dominate the low energy collision-induced dissociation (CID) mass spectra (3); however, the high energy CID mass spectra show (3)(4)(5) significant fragmentation by way of alkane elimination.…”

Collision-induced dissociation mass spectra of protonated alkyl amines

“…Finally, it should be noted that the high energy CID mass spectrum observed for protonated diethyl amine is in quantitative disagreement with spectra that have been reported earlier (3,4), these earlier spectra being in disagreement with each other. Our major disagreement with the spectrum of Sigsby et al …”

“…This conclusion is supported by theoretical calculations on protonated i-propyl amine, which showed that there was a large energy barrier for the concerted elimination of CH4 (1). Nevertheless, the limited high energy collision-induced dissociation (CID) studies of protonated amines have shown that significant fragmentation occurs by way of alkane elimination for species activated in this fashion (3,4).…”

“…These earlier studies (3,4) of the high energy CID of protonated alkyl amines have been exploratory in nature and have not clearly established how general alkane elimination is nor how useful CID studies are in distinguishing between isomeric amines; in particular, there do not-appear to have been any studies of the low energy CID of protonated alkyl amines. In 'present address: Ontario Ministry of the Environment, 125 Resources Road, Rexdale, Ont., Canada.…”