Kinetics and mechanism of nucleophilic displacements with heterocycles as leaving groups. 26. Collisionally activated dissociation of N-alkylpyridinium cations to pyridine and alkyl cations in the gas phase

Katritzky, Alan R.; Watson, Clifford H.; Dega‐Szafran, Z.; Eyler, John R.

doi:10.1021/ja00163a001

Cited by 78 publications

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“…The p-substituted methyl-(CH 3 ), chloro-(Cl), cyano-(CN), and nitro (NO 2 ) benzylpyridinium compounds were synthesized by condensation of the p-substituted benzyl halide with pyridine followed by recrystallization from diethyl ether as described by Katritzky et al [17]. Pyridine, nitromethane, anhydrous diethyl ether, anhydrous ethanol, and the benzyl halide starting reagents were all used without further purification (Sigma-Aldrich, St. Louis, MO, USA).…”

Section: Synthesis and Preparation Of Para-substituted Benzylpyridinimentioning

confidence: 99%

Comparison of the internal energy deposition of direct analysis in real time and electrospray ionization time-of-flight mass spectrometry

Harris¹,

Hostetler²,

Hampton³

et al. 2010

J Am Soc Mass Spectrom

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The internal energy (E int ) distributions of a series of p-substituted benzylpyridinium ions generated by both direct analysis in real time (DART) and electrospray ionization (ESI) were compared using the "survival yield" method. DART mean E int values at gas flow rates of 2, 4, and 6 L min Ϫ1 , and at set temperatures of 175, 250, and 325°C were in the 1.92-2.21 eV range. ESI mean E int at identical temperatures in aqueous and 50% methanol solutions ranged between 1.71 and 1.96 eV, and 1.53 and 1.63 eV, respectively. Although the results indicated that ESI is a "softer" ionization technique than DART, there was overlap between the two techniques for the particular time-of-flight mass spectrometer used. As a whole, there was an increase in E int with increasing reactive and drying gas temperatures for DART and ESI, respectively, indicating thermal ion activation. Three dimensional computational fluid dynamic simulations in combination with direct temperature measurements within the DART ionization region revealed complex inversely coupled fluid-thermal phenomena affecting ion E int values during atmospheric transport. Primarily, that DART gas temperature in the ionization region was appreciably less than the set gas temperature of DART due to the set gas flow rates. There was no evidence of E int deposition pathways from metastable-stimulated desorption, but fragmentation induced by high-energy helium metastables was observed at the highest gas flow rates and temperatures. (J Am Soc Mass Spectrom 2010, 21, 855-863)

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Section: Synthesis and Preparation Of Para-substituted Benzylpyridinimentioning

confidence: 99%

Comparison of the internal energy deposition of direct analysis in real time and electrospray ionization time-of-flight mass spectrometry

Harris¹,

Hostetler²,

Hampton³

et al. 2010

J Am Soc Mass Spectrom

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“…Quantitative CAD experiments on related quaternary pyridinium molecules suggest that the loss of pyridine is not likely to require more than ~60 kcal/mol activation energy but may require 132 substantially less. 24 This can be regarded as the upper limit for the activation barrier to…”

Section: Scheme 62 Potential Carbene Scrambling Via Oxirene (Not Obsmentioning

confidence: 99%

Gas-Phase Synthesis of Charged Copper and Silver Fischer Carbenes from Diazomalonates: Mechanistic and Conformational Considerations in Metal-Mediated Wolff Rearrangements

et al. 2003

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J. Am. Chem. Soc. 2003, 125(15), 4478-4486. IntroductionThe gas phase synthesis of metallo-carbenoid compounds has a surprisingly long history. 1 In early studies, the metallo-carbenoids were created by high energy methods utilizing electron impact ionization. The resulting ions were then used in bimolecular reactions with various neutral molecules to study the chemistry of and determine metalcarbon bond strengths for these charged Fischer carbenes. The importance of studying gas phase species in determining the mechanistic pathways for olefin metathesis was also realized early on, 1b and more recent studies have taken advantage of electrospray ionization (ESI) to continue this work. 2 Gas phase experiments have also enabled mechanistic studies with other highly reactive metallo-carbenoid species. 3 116The utility of diazo compounds as carbene and metallo-carbenoid precursors has been heavily exploited in solution phase chemistry. 4 The use of diazo compounds as precursors in gas phase mass spectrometry (MS) remains less explored. We have recently reported that diazo compounds are excellent carbene precursors for MS. 5 In these experiments, a carbene is produced through the low-energy collision activated dissociation (CAD) 6 of a diazo compound. The resulting loss of N 2 and generation of the carbene is achieved under conditions sufficiently mild that non-covalently bound complexes are not dissociated in the process. The highly reactive carbene then inserts into the guest and converts the noncovalent complex into a covalently bound molecule.All of the molecules in this previous study were based on the diazomalonate core (with at least one 18-crown-6 crown ether attached). These reagents have been appropriately named "molecular mousetraps." 5Diazomalonates 7 (such as 6.1 and 6.2 above) and related diazo ketones 8 are known to undergo Wolff rearrangement in the gas phase as shown in Scheme 6.1. Since its discovery in 1902, the Wolff rearrangement 9 has been the subject of numerous studies. 10 In the present work we use the benefits of gas phase experiments to study the mechanism of multiple, consecutive Wolff rearrangements observed in diazomalonates. 7 The effects that various coordinated metal ions and other charged groups have on Wolff rearrangements are discerned from gas phase MS experiments. Theory is used to quantitatively assess each intermediate for the proposed mechanism. Although the solution phase synthesis of stable copper (I) and silver (I) Fischer carbenes has been 117 known for some time, 11 here we report the first gas phase synthesis of copper (I) and silver (I) Fischer carbenes. The results for several intermolecular reactions of these carbenes with various adduct molecules are presented.Scheme 6.1 Experimental MethodologyAll mass spectra were acquired on an LCQ Classic instrument from Finnigan.Solutions of the reagents in the ~30-80 µM range were electrosprayed from a ~80/20(v/v) solution of methanol/water with a minimum of 0.1% MeCN added. Soft ionization settings were used to maximize th...

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“…The extent of fragmentation is correlated with the activation energy (or energy barrier E b ) for dissociation. If it is assumed that the dissociation proceeds via a loose transition state (simple bond cleavage) [5,6] with no reverse energy barrier (see figure 2), E b is assumed to be equal to ΔH f (F + ) + ΔH f (Py) -ΔH f (M + ) [4]. According to the nature and the position of the substituent R, the energy barrier changes: the more electron-withdrawing the substituent, the higher the energy barrier for pyridine loss, and the slower the reaction 1.…”

Section: Introductionmentioning

confidence: 99%

Kinetics of solvent addition on electrosprayed ions in an electrospray source and in a quadrupole ion trap

Gabelica

Lemaire

Laprévôte

et al. 2001

International Journal of Mass Spectrometry

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:Benzylpyridinium cations readily fragment in the electrospray source by loss of pyridine to give benzyl cations (M -79). The full-scan spectra obtained with some instruments also show, in addition, an m/z (M -38) peak corresponding to the addition of acetonitrile, being present in the solvent mixture, on the benzyl cations. Here we report that the addition reaction can occur in the source region of ES-MS instruments, and in a quadrupole ion trap. The kinetics of acetonitrile addition was monitored in an ion trap, acetonitrile being provided by leakage from the source, through the heated capillary. For benzyl ions with different substituents, the addition kinetics has been found positively correlated with the Brown parameter σ + of the benzyl radical, and therefore with the effective charge density on the α-carbon atom of the benzyl ion. This is consistent with the Langevin or ADO theory of ion-molecule reaction kinetics.Introduction :

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Kinetics and mechanism of nucleophilic displacements with heterocycles as leaving groups. 26. Collisionally activated dissociation of N-alkylpyridinium cations to pyridine and alkyl cations in the gas phase

Abstract: Many VV-alkylpyridinium cations undergo collisionally activated dissociation in the gas phase to form pyridine and

Cited by 78 publications

References 0 publications

Comparison of the internal energy deposition of direct analysis in real time and electrospray ionization time-of-flight mass spectrometry

Comparison of the internal energy deposition of direct analysis in real time and electrospray ionization time-of-flight mass spectrometry

Gas-Phase Synthesis of Charged Copper and Silver Fischer Carbenes from Diazomalonates: Mechanistic and Conformational Considerations in Metal-Mediated Wolff Rearrangements

Kinetics of solvent addition on electrosprayed ions in an electrospray source and in a quadrupole ion trap

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