Mass spectrometry — the appearance potentials of “meta-stable peaks” in some aromatic nitro compounds — a chemical reaction in the mass spectrometer

Beynon, J. H.; Hopkinson, J. A.; Lester, Gabriel

doi:10.1016/0020-7381(69)80025-2

Cited by 41 publications

(5 citation statements)

References 17 publications

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“…This is not a trivial point. The process of lowest energy requirement for pyridine is loss of [H,C,N] with a reported appearance energy AE(C 4 H 4 •+ ) = 13.28 eV, i.e., the critical energy for the reaction is 4.0 eV. Given this large value, almost 100 kcal/mol, it could reasonably be expected that the C 5 H 5 N •+ isomers are able to interconvert prior to undergoing their unimolecular dissociation.…”

Section: Resultsmentioning

confidence: 99%

Observation of the Hammick Intermediate: Reduction of the Pyridine-2-ylid Ion in the Gas Phase

et al. 1996

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Azacyclohexatriene-2-ylidene (1), the 2-isomer of pyridine (2), has been generated by one-electron reduction of the corresponding radical cation in neutralization−reionization mass spectrometric experiments. The experimental finding that this molecule is stable on the microsecond time scale is in agreement with results of quantum chemical calculations that indicate both 1 and its radical cation, 1•+ , correspond to minima on the C5H5N and C5H5N•+ potential energy surfaces. The calculations predict that 1 is less stable than pyridine, 2, by 50 and 49 kcal/mol (MP2/6-31G** and CASSCF-MP2/6-31G**, respectively) or 47 kcal/mol (B3LYP/6-31G**), whereas the radical cations 1•+ and 2•+ are much closer in energy. The ylid ion 1•+ is predicted to be 6 and 7 kcal/mol lower in energy than 2•+ at the MP2 and CASSCF-MP2/6-31G** levels, respectively, and 1 kcal/mol higher according to the hybrid density functional theory. Calculations also suggest that facile isomerization of the ions is prohibited by an energy barrier, amounting to 62 and 57 kcal/mol at MP2/6-31G** and B3LYP/6-31G**, respectively, relative to 1•+ , which is even larger than the 38 kcal/mol obtained at both levels of theory required for the neutral transformation. Despite the substantial impediments, isomerization of excited species is possible since the lowest dissociation channels lie even higher in energy but the experimental observations confirm that neither the ions or neutrals undergo particularly facile isomerization. Using known thermochemical data a value for ΔH f (1•+ ) = 237 ± 5 kcal/mol was obtained from the measured appearance energy, 10.14 eV, of the C5H5N•+ ion generated from methyl picolinate, which is completely consistent with the theoretical predictions of 237−242 kcal/mol derived from the calculated energy differences between the various species and the known heat of formation of 2.

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Section: Resultsmentioning

confidence: 99%

Observation of the Hammick Intermediate: Reduction of the Pyridine-2-ylid Ion in the Gas Phase

et al. 1996

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“…Although considerable reaction chemistry was found, double resonance showed the reactant ion was not [CeHe]"1"• but rather the molecular ion of the olefin. However, with 1,3-butadiene, the following reaction sequence was observed (eq [14][15][16]). [CioH10 lr + h2 (14) c9h9+ + ch3 (15) c8h7+ + ca (16) Pulsed double resonance27 showed that the molecular ion of 1,3-butadiene also reacts with the neutral acyclic CeHé to contribute to formation of the three products.…”

Section: Resultsmentioning

confidence: 99%

“…However, with 1,3-butadiene, the following reaction sequence was observed (eq [14][15][16]). [CioH10 lr + h2 (14) c9h9+ + ch3 (15) c8h7+ + ca (16) Pulsed double resonance27 showed that the molecular ion of 1,3-butadiene also reacts with the neutral acyclic CeHé to contribute to formation of the three products. To correct for the contribution of the [C4H6]"1"•, ion ejection studies27 were initiated to obtain corrected relative rate constants for product ions formed via eq [14][15][16].…”

Section: Resultsmentioning

confidence: 99%

Ion-molecule reaction chemistry of various gas-phase C6H6 radical cations

Gross¹,

Russell²,

Aerni³

et al. 1977

J. Am. Chem. Soc.

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“…We also used two-photon ionization at λ = 258.94 nm, and the results were similar to those obtained using the 0 0 0 resonance ionization. These photons create C 6 H 5 CH 3 •+ ions with excess energy of 0.48 or 0.74 eV, respectively, above the IP, much lower than the excess energy required for ring opening in ionized benzene, 3.5−5.0 eV. − …”

Section: Methodsmentioning

confidence: 99%

“…These photons create C6H5-CH 3 •+ ions with excess energy of 0.48 or 0.74 eV, respectively, above the IP, much lower than the excess energy required for ring opening in ionized benzene, 3.5-5.0 eV. [31][32][33] The laser beam is slightly focused within the center of the cell using a quartz spherical lens (f ) 60 cm, d ) 2.54 cm). The laser output (λ ) 266.76 nm, 100-300 µJ, ∆t ) 15 ns, 10 Hz repetition rate) is generated by an excimer (XeCl) pumped dye laser (Lambda Physik LPX 101 and FL-3002, respectively).…”

Section: Methodsmentioning

confidence: 99%

Coupled Reactions of Condensation and Charge Transfer. 1. Formation of Olefin Dimer Ions in Reactions with Ionized Aromatics. Gas-Phase Studies

et al. 1997

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The toluene radical ion C6H5CH3 •+, generated by resonance two-photon ionization, does not react with a single isobutene molecule (i-C4H8) which has a significantly higher ionization potential (ΔIP = 0.42 eV). However, a reaction is observed involving two i-C4H8 molecules, to form the dimer ion C8H16 •+. A coupled reaction of dimer formation and charge transfer to the dimer is exothermic if the product is an ionized hexene with a low IP. Correspondingly, the observed nominal second-order rate coefficients, (5−25) × 10-12 cm3 s-1, are enhanced by a factor of >105 over the expected value for direct endothermic charge transfer. Pressure and concentration effects suggest a sequential mechanism that proceeds through a C6H5CH3 •+(i-C4H8) reactive π complex. The complex can isomerize to a nonreactive CH3C6H4-t-C4H9 •+ adduct, or react with a second i-C4H8 molecule to form a C6H5CH3 •+(i-C4H8)2 complex, in which the olefin molecules are activated by the aromatic ion. Similar reactions are observed in the benzene/propene system with a somewhat larger ΔIP of 0.48 eV, suggesting that the charge density on the olefin in the complex is still sufficient to activate it for nucleophilic attack. However, aromatic/olefin systems with ΔIP > 0.87 eV show no olefin dimer formation. At low [i-C4H8] and [Ar] number densities, the rate of formation of C8H16 •+ is proportional to [i-C4H8]2[Ar]. The corresponding fourth-order rate coefficient shows a strong negative temperature coefficient with k = 11 × 10-42 cm9 s-1 at 300 K and 2 × 10-42 cm9 s-1 at 346 K, suggesting that the mechanism can be efficient in low-temperature industrial and interstellar environments. The direct formation of the dimer bypasses the monomer olefin cation and its consequent side-reactions, and directs the products selectively into radical ion polymerization. The products and energy relationships that apply in the gas phase are observed also in clusters.

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Mass spectrometry — the appearance potentials of “meta-stable peaks” in some aromatic nitro compounds — a chemical reaction in the mass spectrometer

Cited by 41 publications

References 17 publications

Observation of the Hammick Intermediate: Reduction of the Pyridine-2-ylid Ion in the Gas Phase

Observation of the Hammick Intermediate: Reduction of the Pyridine-2-ylid Ion in the Gas Phase

Ion-molecule reaction chemistry of various gas-phase C6H6 radical cations

Coupled Reactions of Condensation and Charge Transfer. 1. Formation of Olefin Dimer Ions in Reactions with Ionized Aromatics. Gas-Phase Studies

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