Water elimination from the keto and enol tautomers of ionised ethylacetate

more stable structure even though at least four such ionic structures (ethyl acetate and its enol, and butanoic acid and its enol) are more stable. In addition, dioxane(+) does not produce fragment ions and neutrals in their most stable configuration. Instead, products which can be formed by simple bond cleavages from dioxane tend to be formed.The RRKM/QET calculated dissociation rates agree extremely well with measured decay rates of internal energy selected metastable dioxane ions. From these data as well as kinetic energy release results for the C3H60+ + CH20 production we conclude that the ion formed has the CH2-0-CH2CH2 structure and has a AHf°298 = 828 ± 8 kJ/mol. This compares very well with an ab initio calculated energy of 833 ± 17 kJ/mol.25 The RRKM/QET calculations also suggest that the transition states, par-ticularly for the m/e 44 and 45 production, are very tight. That is, the transition state structure is a highly strained one.Acknowledgment. Tomas Baer acknowledges his sincere gratitude to Simon Bauer for providing an exciting and stimulating atmosphere during his 4 years at Cornell. Si's enthusiasm for the new and the unexpected were then, and still are now, a constant source of inspiration. We are grateful to the National Science Foundation for the support of a portion of this work. The structure and energetic studies were supported by the Department of Energy.

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“…Phys., 55, 1471 (1971). (11) T. Baer, G. D. Willett, D. Smith, and J. S. Phillips, J. Chem. Phys., 70, 4076 (1979).…”

Section: Methodsmentioning

confidence: 99%

Thermochemistry and dissociation dynamics of state-selected C4H8O2+ ions. 2. Butanoic acid

Butler¹,

Fraser‐Monteiro²,

Fraser-Monteiro³

et al. 1982

J. Phys. Chem.

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“…The molecular ion of the latter, CH 3 Here then is another example where isotopic labelling fails to indicate a mechanism, but this failure nevertheless shows the way in which a computational exercise must proceed, namely it must show how the positional identity of both labels is lost prior to fragmentation. Another noteworthy feature of the above experimental study 27 was that…”

Section: The Dissociation Of Low-energy Methylacetate Ions : An Unexpmentioning

confidence: 88%

Isotopic labelling in mass spectrometry as a tool for studying reaction mechanisms of ion dissociations

Holmes¹,

Jobst²,

Terlouw³

2007

Labelled Comp Radiopharmac

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Perhaps the greatest influence that isotopic labelling experiments have had on organic mass spectrometry is that reaction mechanisms originally borrowed from the chemistry of neutral counterparts have proved to be inadequate for explaining the results. It was therefore necessary to devise completely new types of fragmentation mechanisms and unconventional structures for organic gas-phase cations. In most cases the labelling technique allows one to discover the positions at which the label atoms are found in both the charged and neutral products of an ion's dissociation. These experimental results are often difficult to rationalize by any simple mechanism, but they nearly always indicate how chemical computations should be directed in order for the latter to be able to provide a better mechanistic understanding. This short article describes some significant studies involving D and 18-O labelling that well support the above assertions, using as examples the behaviour of some quite simple organic molecules.

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“…CAD spectra of C,HsQ:' 4 C,flsodc + H pro- The transition state for this reaction would be akin to those for the movement of H 2 0 between the carbons of 'CH,CH20H2+, I 3 , I 4 and other migrations between adjacent carbons in radical cations.' [5][6][7][8][9][10][11][12][13][14][15][16][17][18] In contrast to expectations based on the suggestion2 that a isomerizes to c prior to losing H20, the elimination of water from a gives 'CH2CH2CO+, whereas ionized propanoic acid and its enol give CH3CH=CO+'. ' 'CH2CH2CO+ is the second most stable C H O+' isomer," about 35 kJmol-' above CH,CH&O".…”

Section: Discussionmentioning

confidence: 99%

“…Isomerization of a to distinct intermediates prior to losses of ethene ('CH2CH20CHOH+) and water (CH,CHC(OH);', (c) was suggested to account for an order of magnitude difference in the rate constants for those two processes.2 Conversion to c is plausible, as ionized esters, acids and isomeric ions inter~onvert.~ However, decomposition from an isolated state was also suggested as a possible reason for different decay rates to the different daught e r~.~ Another ionized ethyl ester, ethyl acetate, also eliminates water in its lowest energy decomposition^.^*^ This elimination produces predominantly CH3CO+'CH=CH2 accompanied by considerable H exchange. 6 However, the steps in this pathway to loss of water remain a mystery. To determine whether a isomerizes to CH,CH,C02H+' (b) and c before losing H 2 0 , we studied the low-energy decompositions of ionized ethyl formate.…”

Section: Introductionmentioning

confidence: 99%

Formation of^· CH₂CH₂CO ⁺ and C₂H₆^+· in the metastable decompositions of ionized ethyl formate

McAdoo

1992

Org. Mass Spectrom.

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The products of the metastable decompositions of ionized ethyl formate (a) are characterized. The loss of water from a produces 'CH,CH,CO+, a rarely reported product. Loss of H appears to produce CH,=CHC(OH)i. The third decomposition is an unusual formation of C,Hl'. This work demonstrates that a previous supposition that isomerization to different intermediates is involved in the losses of ethene and of water from a is correct.

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Water elimination from the keto and enol tautomers of ionised ethylacetate

Cited by 22 publications

References 4 publications

Thermochemistry and dissociation dynamics of state-selected C4H8O2+ ions. 2. Butanoic acid

Thermochemistry and dissociation dynamics of state-selected C4H8O2+ ions. 2. Butanoic acid

Isotopic labelling in mass spectrometry as a tool for studying reaction mechanisms of ion dissociations

Formation of^· CH₂CH₂CO ⁺ and C₂H₆^+· in the metastable decompositions of ionized ethyl formate

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Water elimination from the keto and enol tautomers of ionised ethylacetate

Cited by 22 publications

References 4 publications

Thermochemistry and dissociation dynamics of state-selected C4H8O2+ ions. 2. Butanoic acid

Thermochemistry and dissociation dynamics of state-selected C4H8O2+ ions. 2. Butanoic acid

Isotopic labelling in mass spectrometry as a tool for studying reaction mechanisms of ion dissociations

Formation of· CH2CH2CO + and C2H6+· in the metastable decompositions of ionized ethyl formate

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Formation of^· CH₂CH₂CO ⁺ and C₂H₆^+· in the metastable decompositions of ionized ethyl formate