The decompositions of N-(substituted benzalamino)phthalimide radical cations embody ion-neutral complexes and Stevenson’s rule

Abstract

A previously unreported series of N-(substituted benzalamino)phthalimides was investigated by using the combined techniques of high resolution electron ionization mass spectrometry, metastable decomposition, and collisional activation mass spectrometry. The predominate fragmentation pathway is a McLafferty-type rearrangement. There also occurs, to a lesser extent, a transfer of hydrogen that originates from a substituent remote from the phthalimide moiety and terminates on the phthalimide, The process is interpreted as proceeding via an ion-neutral complex. The effects of substituents on both of the aforementioned fragmentation pathways provide a striking example that gives quantitative evidence for Stevenson's rule. The substituent effects are responsible for a trend in ion abundance that shows a sharp reversal at approximately the ionization energy of the iminium isomer of the phthalimide molecular ion.

A mechanistic study of fragmentation of deprotonated N,2‐diphenyl‐acetamides in electrospray ionization tandem mass spectrometry

“…Some indirect methods have been established to support the INC mechanism, including isotopic labeling experiments, [14,15] kinetic isotope effects, [16,17] kinetic methods, [18,19] and substituent influence. Substituent influence [20][21][22][23][24][25][26] has been widely used to correlate mass spectral intensities in aromatic derivatives ever since substituent constants was introduced to mass spectrometry. [27] In particular, for the competitive ions generated from the INC, there is a good correlation between the two competitive product ions with the σ-substituent constants.…”

Density Functional Theory and Mass Spectrometry of Phthalate Fragmentations Mechanisms: Modeling Hyperconjugated Carbocation and Radical Cation Complexes with Neutral Molecules

“…For the McLafferty+1 rearrangement, the transfer of the second H has been proposed to give an allylic radical [22,30] or a vinyl radical [31]; an allylic or a vinyl radical elimination is possible because the two fragments within the complex are allowed to rotate [26]. The cation molecule complexes (B) show that the vinylic Hs are closer to C-O• at a distance range of 2.37-2.40Å (Figure 3).…”

“…As the two fragments start to separate the charge is partitioned according to Stevenson's rule [26,27]; therefore, Scheme 1 shows the positive charge to remain on the O.…”