Unimolecular Reactions of Diethyl Malonate Cation in Gas-phase

Tajima, Susumu; Ishiguro, Daisuke; Mamada, Masashi; Nakajima, Satoshi

doi:10.5702/massspec.52.263

Cited by 2 publications

(1 citation statement)

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“…For the McLafferty+1 rearrangement, the transfer of the second H has been proposed to give an allylic radical [22,30] or a vinyl radical [31]; an allylic or a vinyl radical elimination is possible because the two fragments within the complex are allowed to rotate [26]. The cation molecule complexes (B) show that the vinylic Hs are closer to C-O• at a distance range of 2.37-2.40Å (Figure 3).…”

Section: Transfer Of Hydrogen Through Radical Cation Molecule Complexmentioning

confidence: 99%

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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