Unimolecular dissociations at short times. A comparison of angle-resolved mass spectrometry and field ionization kinetics

Low Energy Dissociation Processes of Ionized Cyclohexene: A Theoretical Insight,

“…The second dissociation reaction of ionized cyclohexene, 1, is the retro Diels-Alder process. As mentioned in the Introduction, this reaction has been extensively studied experimentally [11][12][13][14][15][16] and theoretically. 7,9,10 Thus, only the salient results will be indicated here.…”

“…The behavior of the latter radical cation has been studied for a long time. [11][12][13][14][15][16][17][18][19] Its major dissociation route, as well as many other [C 6 H 10 ] •+ ions, 14,15 leads to the [C 5 H 7 ] + ion (Scheme 2).…”

“…This latter phenomenon has been suggested to originate from 1,3-allylic-hydrogen shifts on the intact cyclohexene ring. [11][12][13] Direct and reverse cation radical Diels-Alder reactions have been investigated using ab initio molecular orbital calculations by Bauld, 7 Hofmann and Schaefer, 8,9 and Haberl et al 10 The authors conclude that stepwise processes connecting ionized cyclohexene, 1, with the 1,3-butadiene radical cation plus ethylene occur via an open chain distonic intermediate situated ∼140 kJ/mol above ionized cyclohexene.…”

“…Moreover, the exclusive formation of the cylopentenyl structure has also been established from deprotonation energy determination. 5 Deuterium labeling shows that this fragmentation is preceded by a complete H/D exchange when low internal energy precursors are sampled; [11][12][13][14] by contrast, a preferred elimination of a methyl containing a methylene in position 1(1′) (Scheme 2) is noted at short observation times (i.e., at energies high enough to attain a dissociation rate of ∼10 11 s -1 ). [11][12][13] The second dissociation pathway of the cyclohexene radical cation, 1, is the so-called retro Diels-Alder fragmentation which regenerates the 1,3-butadiene radical cation and ethylene (Scheme 2).…”

Four decades of joy in mass spectrometry

“…In the angle‐resolved mass spectrometry experiments the dissociations of high kinetic energy mass selected ions are studied as a function of the laboratory scattering angle, which is related to the internal energy deposition upon collision and hence ion lifetimes (Laramee, Carmody, & Cooks, 1979; Hubik et al, 1980). An excellent agreement between the two methods was observed for the molecules studied, which were 3‐methyl‐3‐buten‐2‐ol, 3‐penten‐2‐ol, and cyclohexene (Burinsky et al, 1981). Of course, such an agreement is obtained if the high kinetic energy mass selected ions have not rearranged to another structure during their flight from the ion source to the collision region.…”