Decarboxylation of metastable methyl benzoate molecular ions

Dechamps, Noémie; Flammang, Robert; Gerbaux, Pascal; Nam, Pham Cam; Nguyen, Minh‐Tho

doi:10.1016/j.jasms.2006.02.015

Cited by 17 publications

(14 citation statements)

References 21 publications

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“…The resulting m/z 206 is stabilized by resonance. Similar mechanism for the initial H rearrangement was previously reported for the elimination of CO 2 from methyl benzoate [39]. Table 1 shows the proposed mechanism in Scheme 2 is energetically feasible.…”

Section: Mechanism For the Formation Of M/z 206supporting

confidence: 72%

Density Functional Theory and Mass Spectrometry of Phthalate Fragmentations Mechanisms: Modeling Hyperconjugated Carbocation and Radical Cation Complexes with Neutral Molecules

Jeilani

Cardelino

Ibeanusi

2011

J. Am. Soc. Mass Spectrom.

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This is the first ab initio study of the energetics of the fragmentation mechanisms of phthalate, by mass spectrometry, leading to protonated phthalic anhydride (m/z 149). Phthalates fragment by two major pathways; namely, the McLafferty+1 rearrangement and the loss of alkoxy. Both pathways involve a carbonyl oxygen attack to the ortho-carbonyl carbon leading to structures with tetrahedral carbon intermediates that eventually give m/z 149. These pathways were studied by collision induced dissociation (CID) using triple quadrupole mass spectrometry. The proposed McLafferty+1 pathway proceeds through a distonic M•+ , leading to the loss of an allylic-stabilized alkene radical. The McLafferty rearrangement step proceeds through a six-membered ring transition state with a small activation energy ranging 0.4-6.2 kcal/mol; the transfer of a second H from the distonic ion of the rearrangement step proceeds through a radical cation molecule complex. Based on quantum chemical modeling of the cation molecule complexes, two kinds of cation molecule complexes were identified as radical cation molecule complex and hyperconjugated cation molecule complex. This distinction is based on the cation and simplifies future modeling of similar complexes. Optimization of important fragments in these pathways showed cyclized and hydrogen-bonded structures to be favored. An exception was the optimized structure of the protonated phthalic anhydride (m/z 149) that showed a structure with an open anhydride ring.

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Section: Mechanism For the Formation Of M/z 206supporting

confidence: 72%

Density Functional Theory and Mass Spectrometry of Phthalate Fragmentations Mechanisms: Modeling Hyperconjugated Carbocation and Radical Cation Complexes with Neutral Molecules

Jeilani

Cardelino

Ibeanusi

2011

J. Am. Soc. Mass Spectrom.

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“…However, CO 2 is a common neutral fragment of a lot of molecules, for instance dicarboxylic and substituted acids, anhydrides and lactones. Metastable methyl benzoate molecular ions were also proven to expel carbon dioxide . Protonated methyl benzoate also eliminates CO 2 upon collisional activation at low dissociation energy .…”

Section: Resultsmentioning

confidence: 99%

“…Metastable methyl benzoate molecular ions were also proven to expel carbon dioxide. 157 Protonated methyl benzoate also eliminates CO 2 upon collisional activation at low dissociation energy. 158 The protonated carbon dioxide HCO 2 + itself is a common fragment of short chain carboxylic acids.…”

Section: Discriminant Variables In the Prediction Modelmentioning

confidence: 99%

Volatile compounds profiling by using proton transfer reaction‐time of flight‐mass spectrometry (PTR‐ToF‐MS). The case study of dark chocolates organoleptic differences

et al. 2019

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Direct‐injection mass spectrometry (DIMS) techniques have evolved into powerful methods to analyse volatile organic compounds (VOCs) without the need of chromatographic separation. Combined to chemometrics, they have been used in many domains to solve sample categorization issues based on volatilome determination. In this paper, different DIMS methods that have largely outperformed conventional electronic noses (e‐noses) in classification tasks are briefly reviewed, with an emphasis on food‐related applications. A particular attention is paid to proton transfer reaction mass spectrometry (PTR‐MS), and many results obtained using the powerful PTR‐time of flight‐MS (PTR‐ToF‐MS) instrument are reviewed. Data analysis and feature selection issues are also summarized and discussed. As a case study, a challenging problem of classification of dark chocolates that has been previously assessed by sensory evaluation in four distinct categories is presented. The VOC profiles of a set of 206 chocolate samples classified in the four sensory categories were analysed by PTR‐ToF‐MS. A supervised multivariate data analysis based on partial least squares regression‐discriminant analysis allowed the construction of a classification model that showed excellent prediction capability: 97% of a test set of 62 samples were correctly predicted in the sensory categories. Tentative identification of ions aided characterisation of chocolate classes. Variable selection using dedicated methods pinpointed some volatile compounds important for the discrimination of the chocolates. Among them, the CovSel method was used for the first time on PTR‐MS data resulting in a selection of 10 features that allowed a good prediction to be achieved. Finally, challenges and future needs in the field are discussed.

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“…Full geometry optimizations and energy calculations were performed, within DFT framework at B3LYP/6‐311++G(d,p) level of theory because B3LYP (Becke, 3‐parameter, Lee‐Yang‐Parr) is one of the most popular functional and can be applied for many different systems . 6‐311++G(d,p) basis set (augmented with diffuse and polarization functions) is recommended for calculations for simple molecules that include electronegative elements and for comparisons with experiment .…”

Section: Methodsmentioning

confidence: 99%

Methyl group transfer upon gas phase decomposition of protonated methyl benzoate and similar compounds

et al. 2018

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Gas phase decompositions of protonated methyl benzoate and its conjugates have been studied by using electrospray ionization-collision induced dissociation-tandem mass spectrometry. Loss of CO molecule, thus transfer of methyl group, has been observed. In order to better understand this process, the theoretical calculations have been performed. For methyl benzoate conjugates, it has been found that position of substituent affects the loss of CO molecule, not the electron donor/withdrawing properties of the substituent. Therefore, electrospray ionization-mass spectrometry in positive ion mode may be useful for differentiation of isomers of methyl benzoate conjugates.

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Decarboxylation of metastable methyl benzoate molecular ions

Cited by 17 publications

References 21 publications

Density Functional Theory and Mass Spectrometry of Phthalate Fragmentations Mechanisms: Modeling Hyperconjugated Carbocation and Radical Cation Complexes with Neutral Molecules

Density Functional Theory and Mass Spectrometry of Phthalate Fragmentations Mechanisms: Modeling Hyperconjugated Carbocation and Radical Cation Complexes with Neutral Molecules

Volatile compounds profiling by using proton transfer reaction‐time of flight‐mass spectrometry (PTR‐ToF‐MS). The case study of dark chocolates organoleptic differences

Methyl group transfer upon gas phase decomposition of protonated methyl benzoate and similar compounds

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