Vibronic structure of alkoxy radicals via photoelectron spectroscopy

Ramond, T.; Davico, Gustavo E.; Schwartz, Rebecca L.; Lineberger, W. C.

doi:10.1063/1.480767

Cited by 141 publications

(174 citation statements)

References 50 publications

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“…The fact that CID of the Meisenheimer complex does not yield substitution products-except for the deprotonation reaction-is probably due to the fact that the methyl group of TNT is not a good leaving group and that TNT has a higher gas-phase acidity (⌬G acid ϭ 309.0 Ϯ 2.0 kcal/mol) [31] than CH 3 NO 2 (⌬G acid ϭ 349.7 Ϯ 2.0 kcal/mol) [32]. The occurrence of deprotonation in this case exactly coincides with the previous observation of Briscese and Riveros [11] of proton transfer in the gas-phase nucleophilic reactions of CH 3 O Ϫ with m-difluorobenzene C 6 H 4 F 2 leading to the production of CH 3 OH and C 6 H 3 F 2 Ϫ , since the higher acidity of C 6 H 4 F 2 (⌬G acid ϭ 366.3 Ϯ 2.0 kcal/mol) [33] compared to that of CH 3 OH (⌬G acid ϭ 375.1 Ϯ 1.1 kcal/mol) [34], prevents the nucleophilic substitution reaction [11].…”

Section: Carbon-bonded Meisenheimer Complexesmentioning

confidence: 99%

Meisenheimer complexes bonded at carbon and at oxygen

Chen

Cooks

2004

J. Am. Soc. Mass Spectrom.

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The carbon-bonded gas-phase Meisenheimer complex of 2,4,6-trinitrotoluene (TNT) and the nitromethyl carbanion CH 2 NO 2 Ϫ (m/z 60) is generated for the first time by chemical ionization using nitromethane as the reagent gas. Collision-induced dissociation (CID) of the Meisenheimer complex furnishes deprotonated TNT, a result of the higher gas-phase acidity of TNT than nitromethane. The formation of Meisenheimer complexes with CH 2 NO 2 Ϫ in the gas phase is selective to highly electron-deficient compounds such as dinitrobenzene and trinitrobenzene and does not occur with organic molecules with lower electron-affinity such as methanol, methylamine, propionaldehyde, acetone, ethyl acetate, chloroform, toluene, m-methoxytoluene, and even nitrobenzene and p-fluoronitrobenzene. As such, the reaction allows selective detection of TNT in mixtures. Meisenheimer complexes between CH 2 NO 2 Ϫ and the three dinitrobenzene isomers display distinctive fragmentations. The oxygen-bonded -complex of TNT with the deprotonated hemiacetal anion CH 3 OCH 2 O Ϫ (m/z 61), represents a different type of Meisenheimer complex. It displays characteristic fragmentation involving loss of HNO 2 upon CID. The combination of a selective ion/molecule reaction (Meisenheimer complex formation) followed by a characteristic CID process provides a second novel and highly selective approach to the detection of TNT and closely related compounds in mixtures. The assay is readily implemented using neutral loss scans in a triple quadrupole mass spectrometer. Gas-phase reactions of denitrosylated TNT with benzaldehyde produce the corresponding dihydrofuran in an aldol condensation, a result that parallels the corresponding condensed-phase reaction. (J Am Soc Mass Spectrom 2004, 15, 998 -1004

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Section: Carbon-bonded Meisenheimer Complexesmentioning

confidence: 99%

Meisenheimer complexes bonded at carbon and at oxygen

Chen

Cooks

2004

J. Am. Soc. Mass Spectrom.

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“…The alternative dissociation pathway by elimination of C 2 H 3 ⅐ , C 2 H 5 OH, and C 2 H 4 of enthalpies of formation 295, † Ϫ235.3 [63], and 52.5 kJ mol Ϫ1 , respectively, requires AE(1 ϩ ) ϭ 13.7 eV. In addi-* From the enthalpy of formation of C 2 H 5 O Ϫ (Ϫ183 to Ϫ186 kJ mol Ϫ1 ) [66,67] and the electron affinity of C 2 H 5 O ⅐ (1.712 eV) [68].…”

Section: Preparation and Dissociations Of [Po 2 H 2 ] ϩ Ionsmentioning

confidence: 99%

Generation and characterization of ionic and neutral P(OH)₂^+/. in the gas phase by tandem mass spectrometry and computational chemistry

Rapole

Srinivas

Bhanuprakash

et al. 2002

J. Am. Soc. Mass Spectrom.

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The bicoordinated dihydroxyphosphenium ion P(OH) 2 ϩ (1 ϩ ) was generated specifically by charge-exchange dissociative ionization of triethylphosphite and its connectivity was confirmed by collision induced dissociation and neutralization-reionization mass spectra. The major dissociation of 1 ϩ forming PO ϩ ions at m/z 47 involved another isomer, O¢POOH 2 ϩ (2 ϩ ), for which the optimized geometry showed a long POOH 2 bond. Dissociative 70-eV electron ionization of diethyl phosphite produced mostly 1 ϩ together with a less stable isomer, HP(O)OH ϩ (3 ϩ ). Ion 2 ϩ is possibly co-formed with 1 ϩ upon dissociative 70-eV electron ionization of methylphosphonic acid. Neutralization-reionization of 1 ϩ confirmed that P(OH) 2 ⅐ (1) was a stable species. Dissociations of neutral 1, as identified by variable-time measurements, involved rate-determining isomerization to 2 followed by fast loss of water. A competitive loss of H occurs from long-lived excited states of 1 produced by vertical electron transfer. The A and B states undergo rate-determining internal conversion to vibrationally highly excited ground state that loses an H atom via two competing mechanisms. The first of these is the direct cleavage of one of the OOH bonds in 1. The other is an isomerization to 3 followed by cleavage of the POH bond to form O¢POOH as a stable product. The relative, dissociation, and transition state energies for the ions and neutrals were studied by ab initio and density functional theory calculations up to the QCISD(T)/6 -311ϩG(3df,2p) and CCSD(T)/aug-cc-pVTZ levels of theory. RRKM calculations were performed to investigate unimolecular dissociation kinetics of 1. Excited state geometries and energies were investigated by a combination of configuration interaction singles and time-dependent density functional theory calculations. (J Am Soc Mass Spectrom 2002, 13, 250 -264)

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“…23 There was significantly less vibronic coupling observed for the isopropoxy and tert-butoxy radicals. 22,27 While the work on interpreting the photoelectron spectra of the ethoxide anion yielded results that needed to be analyzed with the inclusion of Jahn-Teller distortions and vibronic coupling, 22,23,25,28 recent calculations suggest this will not be the case for hydroxymethoxy. 26 Eisfeld and Francisco 11 studied low lying electronic states of H 2 C(OH)O • , focusing on calculating its electronic absorption spectra (CASSCF/CASPT2, CASSCF/MRCI+Q).…”

Section: Introductionmentioning

confidence: 99%

“…Previous experimental and theoretical work studied the effect of methyl substitutions, forming ethoxy, isopropoxy, and tert-butoxy radicals. [22][23][24][25][26][27] The substitution of a methyl group for a hydrogen atom will change the electronic structure of the methoxy radical, breaking its C 3v symmetry. For the ethoxy radical, significant Jahn-Teller distortions were observed in the CH 3 CH 2 O -photoelectron spectrum, where the CH 3 CH 2 O • state was found to be only 355 cm -1 higher in energy than the ground state.…”

Section: Introductionmentioning

confidence: 99%

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Photoelectron spectroscopy of the hydroxymethoxide anion, H2C(OH)O−

Oliveira

Lehman

McCoy

et al. 2016

The Journal of Chemical Physics

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We report the negative ion photoelectron spectroscopy of the hydroxymethoxide anion, H2C(OH)O−. The photoelectron spectra show that 3.49 eV photodetachment produces two distinct electronic states of the neutral hydroxymethoxy radical (H2C(OH)O⋅). The H2C(OH)O⋅ ground state (X̃ 2A) photoelectron spectrum exhibits a vibrational progression consisting primarily of the OCO symmetric and asymmetric stretches, the OCO bend, as well as combination bands involving these modes with other, lower frequency modes. A high-resolution photoelectron spectrum aids in the assignment of several vibrational frequencies of the neutral H2C(OH)O⋅ radical, including an experimental determination of the H2C(OH)O⋅ 2ν12 overtone of the H–OCO torsional vibration as 220(10) cm−1. The electron affinity of H2C(OH)O⋅ is determined to be 2.220(2) eV. The low-lying Ã 2A excited state is also observed, with a spectrum that peaks ∼0.8 eV above the X̃ 2A state origin. The Ã 2A state photoelectron spectrum is a broad, partially resolved band. Quantum chemical calculations and photoelectron simulations aid in the interpretation of the photoelectron spectra. In addition, the gas phase acidity of methanediol is calculated to be 366(2) kcal mol−1, which results in an OH bond dissociation energy, D0(H2C(OH)O–H), of 104(2) kcal mol−1, using the experimentally determined electron affinity of the hydroxymethoxy radical.

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Vibronic structure of alkoxy radicals via photoelectron spectroscopy

Cited by 141 publications

References 50 publications

Meisenheimer complexes bonded at carbon and at oxygen

Meisenheimer complexes bonded at carbon and at oxygen

Generation and characterization of ionic and neutral P(OH)₂^+/. in the gas phase by tandem mass spectrometry and computational chemistry

Photoelectron spectroscopy of the hydroxymethoxide anion, H2C(OH)O−

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Vibronic structure of alkoxy radicals via photoelectron spectroscopy

Cited by 141 publications

References 50 publications

Meisenheimer complexes bonded at carbon and at oxygen

Meisenheimer complexes bonded at carbon and at oxygen

Generation and characterization of ionic and neutral P(OH)2+/. in the gas phase by tandem mass spectrometry and computational chemistry

Photoelectron spectroscopy of the hydroxymethoxide anion, H2C(OH)O−

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Generation and characterization of ionic and neutral P(OH)₂^+/. in the gas phase by tandem mass spectrometry and computational chemistry