Acetone Radical Cation Research Articles

Dissociation of Acetone Radical Cation (CH3COCH3+· → CH3CO+ + CH3·): An Ab Initio Direct Classical Trajectory Study of the Energy Dependence of the Branching Ratio

The nonstatistical dissociation of acetone radical cation has been studied by ab initio direct classical trajectory calculations at the MP2/6-31G(d) level of theory. A bond additivity correction has been used to improve the MP2 potential energy surface (BAC-MP2). The energy dependence of the branching ratio, dissociation kinetics, and translational energy distribution for the two types of methyl groups have been investigated using microcanonical ensembles and specific mode excitation. In each case, the dissociation favors the loss of the newly formed methyl group, in agreement with the experiments. For microcanonical ensembles, the branching ratios for methyl loss are calculated to be 1.43, 1.88, 1.70, and 1.50 for 1, 2, 10, and 18 kcal/mol of excess energy, respectively. The energy dependence of the branching ratio is seen more dramatically in the excitation of individual modes involving C-C-O bending. For modes 3 and 6, the branching ratio rises to 1.6 and 1.8-2.3 when 1 or 2 kcal/mol are added, respectively, but falls off when more energy is added. For mode 8, the branching ratio continues to rise monotonically from 1.5 to 2.76 when 1-8 kcal/mol of excess energy are added.

Suppression of the Methyl Radical Loss from Acetone Cation within (CH3COCH3)n{CH3COCH3}+Clusters

We have investigated the photophysics of the acetone radical cation in the vacuum ultraviolet energy region by multiphoton ionization combined with time-of-flight mass spectrometry in a cluster beam. We have found that the loss of methyl radical from the acetone radical cations is remarkably suppressed at 10.5 eV when they are solvated by a few neutral acetone molecules. The cluster ion mass spectra obtained by nanosecond and picosecond laser pulses reveal that there are intermolecular processes, occurring in several tens of picoseconds, which are responsible for the survival of the acetone cations in clusters. This remarkable solvation effect on the yield of the methyl radical loss from the acetone cation can be rationalized by the intracluster vibrational energy redistribution and the self-catalyzed enolization which compete with the methyl radical loss process.

Dissociation of acetone radical cation (CH3COCH3+˙ → CH3CO++CH3˙): An ab initio direct classical trajectory study

The dissociation of acetone radical cation (CH3COCH3+˙ → CH3CO+ + CH3˙) has been studied by ab initio direct classical trajectory calculations at the MP2/6-31G(d) level of theory. A total of 247 trajectories were initiated at the transition state of the keto–enol tautomerization. A microcanonical ensemble using quasiclassical normal mode sampling was constructed by distributing 10 kcal mol−1 of excess energy above the barrier. The dissociation is found to favor the loss of the newly formed methyl group in agreement with experiments. The branching ratio of methyl loss was calculated to be 1.53 ± 0.20 which is fortuitously in very good agreement with the experimental ratio of 1.55 for 8–12 kcal mol−1 excess energy. Nearly 50% of the available energy is retained by the acetyl fragment as vibrational energy. The methyl fragment has very little vibrational energy but receives ca. 25% of the available energy in translation. The translational energy distribution of the methyl radicals is bimodal with the newly formed methyl having higher average translational energy than that the methyl derived from the spectator group.

Nonstatistical Dynamics in Deep Potential Wells: A Quasiclassical Trajectory Study of Methyl Loss from the Acetone Radical Cation [J. Am. Chem. Soc. 2002, 124, 8512−8513

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionNonstatistical Dynamics in Deep Potential Wells: A Quasiclassical Trajectory Study of Methyl Loss from the Acetone Radical Cation [J. Am. Chem. Soc. 2002, 124, 8512−8513]. Jeremiah A. Nummela and Barry K. CarpenterCite this: J. Am. Chem. Soc. 2002, 124, 49, 14810Publication Date (Web):November 14, 2002Publication History Published online14 November 2002Published inissue 1 December 2002https://doi.org/10.1021/ja0251165Copyright © 2002 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views299Altmetric-Citations1LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (20 KB) Get e-Alerts Get e-Alerts

Nonstatistical dynamics in deep potential wells: a quasiclassical trajectory study of methyl loss from the acetone radical cation.

The loss of methyl radical from the acetone radical cation, following its formation from the enol isomer, has been found to be nonergodic. The origins of this behavior are probed computationally by a quasiclassical trajectory simulation on an AM1-SRP potential energy surface. Experimental reaction outcomes are qualitatively reproduced, and evidence is presented that coherent excitation of the CCO angle bending during isomerization is a significant factor in the nonstatistical behavior.

Self-catalysis in the gas-phase: enolization of the acetone radical cation

Because of a prohibitively large barrier, the solitary acetone radical cation, CH 3C(O)CH 3 + ( 1 +) does not rearrange, neither spontaneously nor by activation, to its more stable enol isomer, CH 2C(OH)CH 3 + ( 1a +). However, this isomerization occurs smoothly by an ion–molecule interaction with neutral acetone itself. The dimer radical cation, [ 1 +⋯ 1 ], generated under conditions of chemical ionization dissociates to m/ z 58 and collision-induced dissociation (CID) experiments show that these ions have the enol structure 1a +. Labeling experiments indicate that the reaction can be viewed as a simple 1,3-hydrogen shift within the acetone radical cation of the complex. Ab initio calculations at the CBS-Q/DZP level of theory indicate that this isomerization is best described as a proton transport catalysis rather than as a spectator model. Our calculations show that the incipient radical formed during the proton abstraction is not CH 3C(O)CH 2 , but rather the less stable configuration CH 3C(O )CH 2 stabilized by CH 3C(OH)CH 3 +. This behaviour can be rationalized by arguments based on ion-dipole interactions. The incipient radical CH 3C(O )CH 2 is transformed to its more stable configuration CH 3C(O)CH 2 via surface crossing. However, this process does not occur via the usual “minimum to minimum crossing” but rather by the novel process of “transition state to minimum crossing”. The abstracted proton is then donated back to the oxygen atom of CH 3C(O)CH 2 to yield the hydrogen-bridged radical cation [ 1a +⋯ 1 ]. The observed tautomerization of the acetone radical cation by acetone itself can be viewed as “self-catalysis”.

Multiphoton ionisation of acetone at 355 nm: a time-of-flight mass spectrometry study

Multiphoton ionisation/fragmentation of acetone has been studied at λ=355 nm using time-of-flight mass spectrometry. A broad peak at m/ e=43 is observed which shows a three-photon laser power dependence. The results suggest that three-photon ionisation at 355 nm produces vibrationally excited acetone ions which undergo fast dissociation. The broadening of the m/ e=43 peak is found to depend on the laser power in the low laser intensity region. Under high laser intensity conditions, a bimodal distribution of m/ e=43 peak was observed which has been assigned to two different isomeric product channels. The results provide clear evidence for partial isomerisation of the keto form of the acetone radical cation to the enol form. On ionisation at 355 nm, CH 3COC 2H 5 fragments into two channels corresponding to (CH 3CO +) and (C 2H 5CO +) in the ratio of approximately 3:1.

Enolization of Gaseous Acetone Radical Cations: Catalysis by a Single Base Molecule

Enolization of Gaseous Acetone Radical Cations: Catalysis by a Single Base Molecule

Electron and proton transfer reactions of simple aldehyde and ketone radical cations and their enol and distonic isomers

The reactivity of the keto and enol isomers of the acetaldehyde and acetone radical cations and the keto, enol and distonic isomers of the propanal radical cation was examined in the gas phase by using Fourier-transform ion cyclotron resonance mass spectrometry. The results obtained show that these radical cations do not readily undergo isomerization within a gas-phase collision complex. Further, the ions favor electron transfer to proton transfer whenever the former reaction is thermodynamically accessible. This reaction can occur either directly by abstraction of an electron by the radical cation or indirectly by a more complex mechanism that is likely to involve energetically favorable proton and hydrogen atom transfers within the ion-molecule complex (a H +/H shuttle). The above knowledge can be utilized in the differentiation of the keto, enol, and distonic isomers of simple carbonyl-containing radical cations.

Infrared multiple photon dissociation of acetone radical cation. An enormous isotope effect with no apparent tunneling

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTInfrared multiple photon dissociation of acetone radical cation. An enormous isotope effect with no apparent tunnelingThomas H. Osterheld and John I. BraumanCite this: J. Am. Chem. Soc. 1992, 114, 18, 7158–7164Publication Date (Print):August 1, 1992Publication History Published online1 May 2002Published inissue 1 August 1992https://doi.org/10.1021/ja00044a031RIGHTS & PERMISSIONSArticle Views118Altmetric-Citations21LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (947 KB) Get e-Alerts Get e-Alerts

Rearrangement and dissociative processes in the [C3H6O]+˙ potential energy surface. Methyl vinyl ether: An example of non‐ergodic behaviour?

AbstractThe unimolecular dissociation reaction of the methyl vinyl ether radical cation to acetyl cation plus methyl radical was studied by means of 13C labelling and tandem mass spectrometric techniques. The results are in good agreement, in all major aspects, with previous data for 13C‐labeled propene oxide. The data are discussed in terms of non‐ergodic behaviour. Isomerization of the methoxyethylidene radical cation intermediate to the acetone radical cation is ruled out on the basis of the labelling experiments and comparison with the hydroxymethene radical cation system.

The gas phase ion chemistry of the acetyl cation and isomeric [C2H3O]+ ions. On the structure of the [C2H3O]+ daughter ions generated from the enol of acetone radical cation

AbstractMethods are described for the unequivocal identification of the acetyl, [CH3\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document} O] (a), 1‐hydroxyvinyl, [CH2\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}OH] (b), and oxiranyl, (d), cations. They involve the careful examination of metastable peak intensities and shapes and collision induced processes at very low, high and intermediate collision gas pressures. It will be shown that each [C2H3O]+ ion produces a unique metastable peak for the fragmentation [C2H3O]+ → [CH3]++CO, each appropriately relating to different [C2H3O]+ structures. [CH3\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}O] ions do not interconvert with any of the other [C2H3O]+ ions prior to loss of CO, but deuterium and 13C labelling experiments established that [CH2\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}OH] (b) rearranges via a 1,2‐H shift into energy‐rich leading to the loss of positional identity of the carbon atoms in ions (b). Fragmentation of b to [CH3]++CO has a high activation energy, c. 400 kJ mol−1. On the other hand, , generated at its threshold from a suitable precursor molecule, does not rearrange into [CH2\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}OH], but undergoes a slow isomerization into [CH3\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}O] via [CH2\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}HO]. Interpretation of results rests in part upon recent ab initio calculations.The methods described in this paper permit the identification of reactions that have hitherto lain unsuspected: for example, many of the ionized molecules of type CH3COR examined in this work produce [CH2\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}OH] ions in addition to [CH3\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}O] showing that some enolization takes place prior to fragmentation. Furthermore, ionized ethanol generates a, b and d ions. We have also applied the methods for identification of daughter ions in systems of current interest. The loss of OH˙ from [CH3COOD]+˙ generates only [CH2\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}OD]. Elimination of CH3˙ from the enol of acetone radical cation most probably generates only [CH3\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}O] ions, confirming the earlier proposal for non‐ergodic behaviour of this system. We stress, however, that until all stable isomeric species (such as [CH3\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^{\rm + } $\end{document}C:]) have been experimentally identified, the hypothesis of incompletely randomized energy should be used with reserve.