Dissociation behavior of ionized valeramide Part 1.: Experimental studies

The unimolecular dissociation of ionized valeramide (n-C4H9CONH2) is examined by mass spectrometric techniques. Photoionization (PI) experiments yield an ionization energy of 9.40+/-0.03 eV. Besides the formation of the molecular ion, dissociation is observed close to the onset of PI. In addition to the PI experiments, the unimolecular dissociations of metastable valeramide ions generated by electron ionization (EI) are examined by means of tandem mass spectrometry, including extensive deuterium labeling studies. The major dissociation processes correspond to competing losses of (i) neutral propene formed via the McLafferty rearrangement and (ii) an ethyl radical to presumably afford protonated acrylamide; losses of methyl radical as well as ethene occur as side reactions. The labeling studies reveal that the McLafferty reaction occurs with high specificity, whereas loss of an ethyl radical is associated with a pronounced, yet by no means complete hydrogen equilibration of the alkyl backbone. While most results of the dissociative PI experiments and the metastable ion (MI) studies agree quite well, significant variations of the ratios Of C3H6 and C2H5. losses in the various experiments do not find an immediate explanation and require further considerations. (Int J Mass Spectrom 214 (2002) 105-128) (C) 2002 Elsevier Science B.V. All rights reserved.