Structural Elucidation of C₆H₄^+. Using Chemical Reaction Monitoring: Charge Transfer Versus Bond Forming Reactions

Abstract

Mass spectrometry is a powerful tool but when used on its own, without specific activation of ions, the ion mass is the single observable and the structural information is absent. One way of retrieving this information is by using ion–molecule reactions. We propose a general method to disentangle isomeric structures by combining mass spectrometry, tunable synchrotron light source, and quantum‐chemistry calculations. We use reactive chemical monitoring technique, which consists in tracking reactivity changes as a function of photoionization energy i. e. the ionic structure. We illustrate the power of this technique with charge transfer reactions of C6H4+. isomers with allene and propyne and discuss its universal applicability. Furthermore, we emphasize the special reactivity characteristics of distonic ions, where strong charge transfer reactivity but very limited reactivity involving bond formation and following cleavages were observed and attributed to the unconventional ortho‐benzyne distonic cation.

Tunable photoionization chemical monitoring (TPI‐CM)—A means to probe molecular ion structures and monitor unimolecular processes through bimolecular ion–molecule reactions: Past, present, and future

“…All calculations were done with the CBS‐QB3 composite method. Figures adapted from Jacovella et al [12] …”

“…The combination of this technique with tunable photoionizing radiation allows to elucidate the structural evolution of the generated ionic species as a function of the internal energy deposited in the molecular system. In other words, it can be used to monitor unimolecular reactions such as dissociative ionization [12] or isomerization [8,13] by tracking changes in reactivity with increasing photon energy. The principle of the tunable photoionization chemical monitoring (TPI-CM) technique is schematically represented in Figure 2.…”

“…This section is followed by detailed explanations of the tunable photoionization chemical monitoring (TPI‐CM) technique, and more specifically using CERISES at the SOLEIL synchrotron. We are then presenting results where TPI‐CM has been used to (i) perform structural elucidation of molecular ion—illustrated with C [12] (ii) monitor the light‐induced isomerization as a function of the internal energy deposited into the system—exemplified with naphthalene/azulene cations interconversion [13] . The last part is a conclusion on what has been done and gives a perspective on what could be done.…”

Monitoring the Light‐induced Isomerisation of the Prototypical Polycyclic Aromatic Hydrocarbons C10H8+ through Ion‐Molecule Reactions

“…We report the structures of C 10 H 8 + species ≈ 80 μs after photoionisation of Azu and Naph – corresponding to a microcanonical rate coefficient of ≈ 10 4 s −1 . This technique was recently successfully used to disentangle the structural diversity of C 6 H 4 + formed upon dissociative ionisation of PA , Azu , and Naph [32] …”

“…This technique was recently successfully used to disentangle the structural diversity of C 6 H 4 + formed upon dissociative ionisation of PA , Azu , and Naph . [32] …”