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Leclerc E Buchmann W Taphanel MH Morizur JP 《Rapid communications in mass spectrometry : RCM》2002,16(7):686-695
Ion/molecule reactions between O=P(OCH(3))(2)(+) phosphonium ions and six aromatic hydrocarbons (benzene, toluene, 1,2,4-trimethylbenzene, naphthalene, acenaphthylene and fluorene) were performed in a quadrupole ion trap mass spectrometer. The O=P(OCH(3))(2)(+) phosphonium ions, formed by electron impact from neutral trimethyl phosphite, were found to react with aromatic hydrocarbons (ArHs) to give (i) an adduct [ArH, O=P(OCH(3))(2)](+) and (ii) for ArHs which have an ionization energy below or equal to 8.14 eV, a radical cation ArH(+ *) by charge transfer reaction. Collision-induced dissociation experiments, which produce fragment ions other than the O=P(OCH(3))(2)(+) ions, indicate that the adduct ions are covalent species. Isotope-labeled ArHs were used to elucidate fragmentation mechanisms. The charge transfer reactions were investigated using density functional theory at the B3LYP/6-311 + G(3df,2p)//B3LYP/6-31G(d,p) level of theory. The potential energy surface obtained from B3LYP/6-31G(d,p) calculations for the reaction between O=P(OCH(3))(2)(+) and benzene is described. 相似文献
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The fragmentations of the acylium ions O?C+? CH2? CH2? CO2CH3 and O?C+? CH2? CH2? COCH3 generated from methyl levulinate are governed extensively by the interaction of the two carbonyl groups. Both species eliminate a molecule of CO unimolecularly and under CID conditions. The results derived from measurements of 13C and 18O labelled precursors, together with kinetic energy release values, have been used to study the mechanisms. In the first of these acylium ions, both carbonyl groups are equivalent; this phenomenon can be the result of a 1,4 methoxy shift. In the second acylium ion, only the oxygen atoms change their positions; this isomerization occurs via the [M? H]+ of γ-valerolactone. Some other fragmentation processes also discussed in relation to 2H labelling are the formation of the [M ? COOCH3] + ion and the loss of HCOOCH3 in the collision-induced dissociation mass spectra of the first acylium ion, and the formation of the [CH3CO]+ ion and the loss of H2O for the second one. 相似文献
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The mass spectra of two series of 2-substituted-2,3-dihydro-4H-pyrans (six ethers and six carbonyl derivatives) showed a marked dependence upon the nature of the substituent. α-Cleavage (substituent loss) was the only primary decomposition observed in the carbonyl series, while ‘retro Diels-Alder’ reactions competed with α-cleavage in the ether series. An unambiguous interpretation of this difference in behaviour, based on the consequence of charge localization and thermochemical data, is proposed. 相似文献
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Ion-molecule reactions between the O=P(OCH(3))(2) (+) phosphonium ions and five aliphatic esters (methyl acetate, methyl propionate, methyl 2-methylpropionate, methyl butyrate and ethyl acetate) were performed in a quadrupole ion trap mass spectrometer. The O=P(OCH(3))(2) (+) phosphonium ions, formed by electron ionization from neutral trimethyl phosphite, were found to react with aliphatic esters to give an adduct ion [RR'CHCOOR", O=P(OCH(3))(2)](+), which loses spontaneously a molecule of ketene CH(2)=CO or substituted ketenes RR'C=CO. Isotope-labeled methyl acetate was used to elucidate fragmentation mechanisms. The potential energy surface obtained from B3LYP/6-31G(d,p) calculations for the reaction between O=P(OCH(3))(2) (+) and methyl acetate is described. 相似文献
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Dorothe Berthomieu Jeanine Tortajada Jean-Pierre Morizur Henri-Edouard Audier 《Journal of mass spectrometry : JMS》1991,26(6):601-607
The reactions of metastable decomposing methyl acetoacetate (a mixture of keto a ad enol tautomers) are reported and discussed. The unimolecular fragmentations of the tautomers are different. The metastable decomposing radical cation of the keto form displays four specific ions: [M –CO]+˙, [M – CH2O]+˙, [M – CH2CO]+˙ and m/z 43. The results derived from D-, 13C- and 18O-labelled precursors together with thermochemical data have been used to study the mechanisms. Experimental results indicate that an unexpected isomerization occurs before dissociation. It formally corresponds to oxygen atom permutation of the two carbonyl groups without participation of the carbon atoms. This remarkable process is interpreted in terms of a mechanism involving ion-molecule complexes. 相似文献
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In connection with work on computerized mass spectral interpretation of organic com-pounds, the behavior of three groups of unsaturated ethers was examined: allylic, substituted allylic and unsaturated ethers with 2 or 3 methylene groups between the oxygen atom and the double bond. A total of 36 compounds (11 labelled) were prepared and mechanistic rationalizations presented. The allylic ethers isomerized to vinylic ethers after ionization. No double bond migration was observed, however, before or after electron-impact of allylic and homoallylic ethers or ethers with 3 methylene groups between the oxygen atom and the double bond. The allylic ethers with seven carbon atoms in the saturated chain lost a saturated alcohol molecule [R' + C3H6OH] by a uni-directional quadruple hydrogen transfer prior to fragmentation. 相似文献