Mass spectrometric and computational studies on the reaction of aromatic peroxyl radicals with phenylacetylene using the distonic radical ion approach

Reactions of a distonic peroxyl radical anion influenced by SOMO–HOMO conversion: an example of anion-directed channel switching

Deprotonation of a remote site in a peroxyl radical energetically buries the singly occupied molecular orbital, suppressing radical-driven oxidation and promoting reactions involving the anion site.

Regioselectivity of aryl radical attack onto isocyanates and isothiocyanates

The combination of multistage mass spectrometry experiments employing the distonic radical approach together with DFT calculations are used to examine addition of the N-methyl-pyridinium-4-yl radical cation (γ-NMP) to iso(thio)cyanates in the gas-phase. The type of products formed depend on the nature of the iso(thio)cyanate: (1) hydrogen atom abstraction occurs for alkyl isocyanates; (2) aryl isocyanates undergo radical-ipso substitution; (3) radical attack occurs at the C[double bond, length as m-dash]C bond of allyl isocyanate; (4) radical attack occurs at the C[double bond, length as m-dash]S bond of isothiocyanates to generate S adducts of γ-NMP and isonitriles. DFT calculations provide insight into the reactivity differences of these heterocumulenes towards the electrophilic C-centered γ-distonic radical cations. Translation of these gas phase results to the solution phase were hampered by dominating radical recombination reactions which appear to be favoured over the radical-iso(thio)cyanate reactions.

Direct Evidence for the Origin of Bis-Gold Intermediates: Probing Gold Catalysis with Mass Spectrometry

Gold-catalyzed alkyne hydration was studied by using in situ reacting mass spectrometry (MS) technology. By monitoring the reaction process in solution under different conditions (regular and very diluted catalyst concentrations, different pH values) and examining the reaction occurrence in the early reaction stage (1-2 ms after mixing) with MS, we collected a series of experimental evidence to support that the bis-gold complex is a potential key reaction intermediate. Furthermore, both experimental and computational studies confirmed that the σ,π-bis-gold complexes are not active intermediates toward nucleophilic addition. Instead, formation of geminally diaurated complex C is crucial for this catalytic process.

Environmental Polymer Degradation: Using the Distonic Radical Ion Approach to Study the Gas-Phase Reactions of Model Polyester Radicals

A novel precursor to the distonic O- and C-centered radical cations Oxo⁺O^• and Oxo⁺C^• was designed and synthesized, which represents model systems for radicals produced during polyester degradation. The precursor is equipped with a nitrate functional group, which serves as a masked site for these alkoxyl and carbon radicals that are unleashed through collision-induced dissociation (CID). Oxo⁺O^• and Oxo⁺C^• feature a cyclic carboxonium ion as permanent charge tag to enable monitoring their ion-molecule reactions on the millisecond to second time scale in the ion trap of the mass spectrometer. The reactions of Oxo⁺O^• and Oxo⁺C^• with cyclohexene, cyclohexadiene, ethyl acetate, 1,1-dimethoxyethane, and 1,2-dimethoxyethane, which exhibit structural features present in both intact and defective polyesters, were explored through product and kinetic studies to identify "hot spots" for radical-induced damage in polyesters. All reactions with Oxo⁺O^• were extremely fast and proceeded predominantly through HAT. Oxo⁺C^• was about two orders of magnitude less reactive and did not noticeably damage aliphatic ester moieties through hydrogen abstraction on the time scale of our experiments. Radical addition to alkene π systems was identified as an important pathway for C-radicals, which needs to be included in polymer degradation mechanisms.

The role of peroxyl radicals in polyester degradation – a mass spectrometric product and kinetic study using the distonic radical ion approach

Mass spectrometric techniques were employed to reveal detailed insight into the reaction of peroxyl radicals with structural motifs in polyesters.

Unimolecular reaction chemistry of a charge-tagged beta-hydroxyperoxyl radical

The study of unimolecular isomerization and decomposition of a charge-tagged β-hydroxyperoxyl radical anion ˙CH₂C(OH)(CH₃)CH₂C(O)O⁻ using mass spectrometry, quantum mechanical calculations and master equation kinetic simulations.