Isolation and characterization of charge-tagged phenylperoxyl radicals in the gas phase: direct evidence for products and pathways in low temperature benzene oxidation

J. Am. Soc. Mass Spectrom.

Blanksby

et al. 2013

Self Cite

. (2013). UV photodissociation action spectroscopy of haloanilinium ions in a linear quadrupole ion trap mass spectrometer. Journal of the American Society for Mass Spectrometry, 24 (6), 932-940. UV photodissociation action spectroscopy of haloanilinium ions in a linear quadrupole ion trap mass spectrometer Abstract UV-vis photodissociation action spectroscopy is becoming increasingly prevalent because of advances in, and commercial availability of, ion trapping technologies and tunable laser sources. This study outlines in detail an instrumental arrangement, combining a commercial ion-trap mass spectrometer and tunable nanosecond pulsed laser source, for performing fully automated photodissociation action spectroscopy on gas-phase ions. The components of the instrumentation are outlined, including the optical and electronic interfacing, in addition to the control software for automating the experiment and performing online analysis of the spectra. To demonstrate the utility of this ensemble, the photodissociation action spectra of 4-chloroanilinium, 4-bromoanilinium, and 4-iodoanilinium cations are presented and discussed. Multiple photoproducts are detected in each case and the photoproduct yields are followed as a function of laser wavelength. It is shown that the wavelength-dependent partitioning of the halide loss, H loss, and NH3 loss channels can be broadly rationalized in terms of the relative carbon-halide bond dissociation energies and processes of energy redistribution. The photodissociation action spectrum of (phenyl)Ag2 + is compared with a literature spectrum as a further benchmark. AbstractUV-Vis photodissociation action spectroscopy is becoming increasingly prevalent due to advances in, and commercial availability of, ion trapping technologies and tunable laser sources. This study outlines in detail an instrumental arrangement, combining a commercial ion-trap mass spectrometer and tunable nanosecond pulsed laser source, for performing fully automated photodissociation action spectroscopy on gas-phase ions. The components of the instrumentation are outlined, including the optical and electronic interfacing, in addition to the control software for automating the experiment and performing online analysis of the spectra. To demonstrate the utility of this ensemble, the photodissociation action spectra of 4-chloroanilinium, 4-bromoanilinium and 4-iodoanilinium cations are presented and discussed. Multiple photoproducts are detected in each case and the photoproduct yields are followed as a function of laser wavelength. It is shown that the wavelength-dependent partitioning of the halide loss, H loss and NH 3 loss channels can be broadly rationalized in terms of the relative carbon-halide bond dissociation energies and processes of energy redistribution. The photodissociation action spectrum of (phenyl)Ag 2 + is compared to a literature spectrum as a further benchmark.3

Section: Resultsmentioning

confidence: 99%

UV Photodissociation Action Spectroscopy of Haloanilinium Ions in a Linear Quadrupole Ion Trap Mass Spectrometer

Hansen

J. Am. Soc. Mass Spectrom.

Blanksby

et al. 2013

Self Cite

“…[21][22][23] Though the intrinsic reactivity of the radical may be perturbed to some degree by the presence of a near-by charge 24 studies on distonic radical ions undertaken using mass spectrometry nonetheless provide useful information on the reactions of their neutral counterparts. [24][25][26][27] A distonic radical ion approach has previously been employed to probe the fate of peroxyl radical intermediates; including, pyridinium-2-ethylperoxyl radical cation, 28,29 N-methylpyridinium-4-peroxyl 27,30 and 4-(N,N,N-trimethylammonium)phenylperoxyl radical cation, 27,31,32 in addition to 4-(N,N,N-trimethylammoniummethyl)phenylperoxyl, 3-(N,N,Ntrimethylammonium)phenylperoxyl, and 4-ammoniumphenylperoxyl radical cations. 32 In each case, these distonic studies provided insight into the reactivity of the neutral radical analogue.…”

Section: Introductionmentioning

confidence: 99%

“…Guided by Kirk et al, 31 it is likely the end-product species could comprise five-membered ring products, such as a charge-tagged methyl-substituted cyclopentadienone species but no such channels were detected in our charge-tagged experiments. This implicates the presence of lower-energy reaction pathways not available to the charge-tagged phenylperoxyl radical systems investigated by Kirk et al…”

mentioning

confidence: 99%

Hydroxyl radical formation in the gas phase oxidation of distonic 2-methylphenyl radical cations

Prendergast

Cooper

Phys. Chem. Chem. Phys.

et al. 2013

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The reactions of distonic 4-(N,N,N-trimethylammonium)-2-methylphenyl and 5-(N,N,Ntrimethylammonium)-2-methylphenyl radical cations (m/z 149) with O 2 are studied in the gas phase using ion-trap mass spectrometry. Photodissociation (PD) of halogenated precursors gives rise to the target distonic charge-tagged methylphenyl radical whereas collision-induced dissociation (CID) is found to produce unreactive radical ions. The PD generated distonic radicals, however, react rapidly with O2 to form [M + O2]•+ and [M + O2 -OH]•+ ions, detected at m/z 181 and m/z 164, respectively. Quantum chemical calculations using G3SX(MP3) and M06-2X theories are deployed to examine key decomposition pathways of the 5-(N,N,N-trimethylammonium)-2-methylphenylperoxyl radical and rationalise the observed product ions. The prevailing product mechanism involves a 1,5-H shift in the peroxyl radical forming a QOOH-type intermediate that subsequently eliminates •OH to yield charge-tagged 2-quinone methide. Our study suggests that the analogous process should occur for the neutral methylphenyl + O2 reaction, thus serving as a plausible source of •OH radicals in combustion environments. The prevailing product mechanism involves a 1,5-H shift in the peroxyl radical forming a QOOH-type intermediate that subsequently eliminates OH to yield charge-tagged 2-quinone methide. Our study suggests that the analogous process should occur for the neutral methylphenyl + O 2 reaction, thus serving as a plausible source of OH radicals in combustion environments.

“…iodide; 3--iodo--N,N,N--trimethylbenzaminium iodide; and 1--(4--iodophenyl)--N,N,N--trimethylmethanaminium iodide, synthesized as described previously [16].…”

Section: Methodsmentioning

confidence: 99%

“…Calculated energies (ΔH0) include unscaled zero--point energy, while Gibbs free energies (ΔG298) include free energy corrections calculated at a temperature of 298.15 K and pressure of 1.0 atm. within our laboratory have demonstrated that both PD and CID of 1 generate A [16,30]. For all experiments subsequently described we have used CID exclusively to generate A.…”

Section: Electronic Structure Calculationsmentioning

confidence: 99%

Does Addition of NO₂ to Carbon-Centered Radicals Yield RONO or RNO₂? An Investigation Using Distonic Radical Ions

J. Am. Soc. Mass Spectrom.

Trevitt

Blanksby

2013

Self Cite

Nitrogen dioxide is used as a "radical scavenger" to probe the position of carbon-centered radicals within complex radical ions in the gas phase. As with analogous neutral radical reactions, this addition results in formation of an [M + NO2](+) adduct, but the structural identity of this species remains ambiguous. Specifically, the question remains: do such adducts have a nitro-(RNO2) or nitrosoxy-(RONO) moiety, or are both isomers present in the adduct population? In order to elucidate the products of such reactions, we have prepared and isolated three distonic phenyl radical cations and observed their reactions with nitrogen dioxide in the gas phase by ion-trap mass spectrometry. In each case, stabilized [M + NO2](+) adduct ions are observed and isolated. The structure of these adducts is probed by collision-induced dissociation and ultraviolet photodissociation action spectroscopy and a comparison made to the analogous spectra of authentic nitro-and nitrosoxy-benzenes. We demonstrate unequivocally that for the phenyl radical cations studied here, all stabilized [M + NO2](+) adducts are exclusively nitrobenzenes. Electronic structure calculations support these mass spectrometric observations and suggest that, under low-pressure conditions, the nitrosoxy-isomer is unlikely to be isolated from the reaction of an alkyl or aryl radical with NO2. The combined experimental and theoretical results lead to the prediction that stabilization of the nitrosoxy-isomer will only be possible for systems wherein the energy required for dissociation of the RO-NO bond (or other low energy fragmentation channels) rises close to, or above, the energy of the separated reactants. AbstractNitrogen dioxide is used as a "radical scavenger" to probe the position of carbon--centered radicals within complex radical ions in the gas phase. As with analogous neutral radical reactions, this addition results in formation of an [M+NO2] + adduct, but the structural identity of this species remains ambiguous. Specifically, the question remains: do such adducts have a nitro--(RNO2) or nitrosoxy--(RONO) moiety, or are both isomers present in the adduct population? In order to elucidate the products of such reactions, we have prepared and isolated three distonic phenyl radical cations and observed their reactions with nitrogen dioxide in the gas phase by ion--trap mass spectrometry. In each case, stabilized [M + NO2] + adduct ions are observed and isolated. The structure of these adducts is probed by collision--induced dissociation and ultraviolet photodissociation action spectroscopy and a comparison made to the analogous spectra of authentic nitro--and nitrosoxy--benzenes. We demonstrate unequivocally that, for the phenyl radical cations studied here, all stabilized [M + NO2] + adducts are exclusively nitrobenzenes. Electronic structure calculations support these mass spectrometric observations and suggest that, under low--pressure conditions, the nitrosoxy--isomer is unlikely to be isolated from the reaction of an alkyl or aryl radical ...