Fragmentation of the metastable molecular ion of methyl lactate: The formation of oxygen-protonated methanol [CH3OH2]+ involving double hydrogen atom transfers

Tajima, Susumu; Nagai, Yukiyoshi; Sekiguchi, Osamu; Fujishige, Masao; Uchida, Nozomu

doi:10.1016/1044-0305(94)00103-7

Cited by 11 publications

(6 citation statements)

References 32 publications

(9 reference statements)

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“…This fragmentation is the same as that of CH 3 OCH 2 + ions formed from the other precursors,13–15 but is different from that of the isomeric ion CH 3 CH + OH ( m/z 45) because the latter ion decomposes into the ions at m/z 19, 27 and 29 16,. 17 Thus the structure of the decomposing m/z 45 ion can reasonably be assigned as CH 3 OCH 2 + . The peak at m/z 29 in Fig.…”

Section: Resultsmentioning

confidence: 85%

Unimolecular metastable decompositions ofgem-dimethoxyalkanes (RR?C(OCH3)2) upon electron impact. I. Dimethoxymethane and 1,1-dimethoxyethane

Takahashi

Higuchi

Sekiguchi

et al. 2000

Rapid Commun. Mass Spectrom.

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The unimolecular metastable decompositions of dimethoxymethane (CH(2)(OCH(3))(2), 1) and 1,1-dimethoxyethane (CH(3)CH(OCH(3))(2), 2) upon electron impact have been investigated by means of mass-analyzed ion kinetic energy (MIKE) spectrometry, collision-induced dissociation (CID) spectrometry and D-labeling techniques. Both molecular ions are formed at extremely low abundance. Sequential transfers of a methyl group and a hydrogen atom to an ether oxygen are observed during the decomposition of [M - H](+) ions from 1 and 2. The [M - H](+) ion from 2 also decomposes into the m/z 43 ion by the loss of dimethyl ether. Almost complete hydrogen exchange is observed prior to the loss of CH(4) from the m/z 45 ion ([M - OCH(3)](+)) of 1. The m/z 59 ions ([M - OCH(3)](+)) of 2 decompose competitively into the m/z 31 and 29 ions by the losses of C(2)H(4) and CH(2)O, respectively. The former loss occurs via two different fragmentation pathways. The relative abundances of the ions in the MIKE spectra increase with decreases in the total heat of formation (Sigma DeltaH(f)) of the ion plus the neutral fragment. Copyright 2000 John Wiley & Sons, Ltd.

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Section: Resultsmentioning

confidence: 85%

Unimolecular metastable decompositions ofgem-dimethoxyalkanes (RR?C(OCH3)2) upon electron impact. I. Dimethoxymethane and 1,1-dimethoxyethane

Takahashi

Higuchi

Sekiguchi

et al. 2000

Rapid Commun. Mass Spectrom.

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“…2. To compare the results of what is already known for the fragmentation of the monomer 42 or the dimeric complex of ligands to a metal ion 43 we show here a much better resolved mass spectrum taken at the electron energy of 70 eV (Fig. 11).…”

Section: Fragmentsmentioning

confidence: 99%

Size-selected methyl lactate clusters: fragmentation and spectroscopic fingerprints of chiral recognition

Fárnı́k

Weimann

Steinbach

et al. 2006

Phys. Chem. Chem. Phys.

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A comprehensive experimental study of the OH stretching vibrations of size-selected clusters of enantiopure and racemic methyl lactate is presented. For the size selection, we measured angular dependent mass spectra and time-of-flight distributions at the different fragment masses. In this way the fragmentation of these clusters upon electron impact ionization is obtained. The largest fragment masses of the neutral (MLac)n clusters are the protonated (MLac)n-1H+ ions. The results of a pressure dependent study in an FTIR jet experiment are compared with completely size-selected experiments based on atomic beam deflection and depletion spectroscopy. The size assignments and spectra agree for dimers and trimers. Structures and spectral information for the trimer and the tetramer at density functional and MP2 level are provided. Selective self-aggregation and chiral recognition was observed for homochiral trimers. They exhibit a ring structure bound by OH...OH hydrogen bonds. A spectacular switch in the hydrogen bonding topology was observed for the tetramer. The homochiral enantiomer exhibits cooperative OH...OH bonding, while the heterochiral version shows isolated OH...O=C bonding in a symmetric SRSR arrangement. The crucial ingredients for this identification are the size-selective IR spectra with their different shifts and line patterns which are reproduced by the calculations.

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“…1,2 The observation of hydrogen transfers, 3,4 hydrogen exchanges, 5 isotopic atom permutations 6 and remote fragmentations 7,8 in many cases are of special interest, and corresponding mechanisms via intermediate ion/neutral complexes have been proposed. -Diketone compounds as important intermediates in organic synthesis have been extensively studied.…”

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confidence: 99%

Ion/Neutral Complex-mediated Reactions Generated from Some Ionized Tetrahydroimidazole-substituted Methylene β-Diketones

She

Liu

1997

Rapid Commun. Mass Spectrom.

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The dissociation of gaseous metastable ions of m/z 153 and the formation of ions of m/z 139 from the unimolecular fragmentations of ionized tetrahydroimidazole-substituted methylene -diketones were examined by tandem mass spectrometry. In addition, some other fragments accompanying the elimination of either an H 2 O molecule or an CHO ᭹ radical were also observed in the collision-induced dissociation spectra of molecular ions of the compounds bearing an aromatic ring. Collision-induced dissociation and isotopic labeling showed that these processes may involve reactions of intermediate ion/neutral complexes and multistep rearrangements. The corresponding mechanisms are discussed. © 1997 by John Wiley & Sons, Ltd. Received 8 January 1997; Revised 8 March 1997; Accepted 10 March 1997 Rapid. Commun. Mass Spectrom. 11, 723-726 (1997 9,10 However, related compounds in which the two hydrogens of the methylene group of -diketones are substituted, as for example in our system, have not been studied. Tandem mass spectrometric techniques, involving collision-induced dissociation (CID) at low energy have now been used for this purpose. Some interesting common characteristic fragmentations in ionized tetrahydroimidazole-substituted methylene -diketones mediated by ion/neutral complexes are reported in this paper. EXPERIMENTALMass spectrometric measurements were performed on a multiple quadrupole instrument (VG Quattro, Fisons Instruments, Manchester, UK) with a source temperature of 200°C. The instrument was operated in the electron ionization mode using an ionization energy of 70 eV and an emission current of 200 µA. The samples were dissolved in acetone and inserted via a desorption probe; samples were loaded onto a rapidly heated wire filament and evaporated with a desorption current of 400 µA. CID spectra and parent-ion spectra were obtained using argon as the collision gas at a collision energy of 50 eV. The pressure of argon was adjusted to reduce the main beam intensity by 50% of its original value.The tetrahydroimidazole-substituted methylene -diketones were synthesized in our laboratory using a method that has been reported previously, 11,12 in which a suitable -diketone was used as starting material, reacting in succession with carbon disulfide, ethyl bromide and ethylenediamine. The products were then purified by recrystallization. The deuterated samples were prepared by the classical method, mixing the sample with an excess of CD 3 OD. RESULTS AND DISCUSSIONSome major ions and corresponding relative abundances observed in the electron ionization (EI) mass spectra of the compounds investigated (1-5) are given in Table 1 (Fig. 2) indicated that the specific fragmentations were derived directly from dissociation of their molecular ions. It is clear that in these cases, the observations cannot be explained by simple bond cleavage and rearrangement; therefore, the experimental results implied that an unexpected and specific skeletal multi-step rearrangement reaction may be occurring before dissociation. In order to o...

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Fragmentation of the metastable molecular ion of methyl lactate: The formation of oxygen-protonated methanol [CH₃OH₂]⁺ involving double hydrogen atom transfers

Cited by 11 publications

References 32 publications

Unimolecular metastable decompositions ofgem-dimethoxyalkanes (RR?C(OCH3)2) upon electron impact. I. Dimethoxymethane and 1,1-dimethoxyethane

Unimolecular metastable decompositions ofgem-dimethoxyalkanes (RR?C(OCH3)2) upon electron impact. I. Dimethoxymethane and 1,1-dimethoxyethane

Size-selected methyl lactate clusters: fragmentation and spectroscopic fingerprints of chiral recognition

Ion/Neutral Complex-mediated Reactions Generated from Some Ionized Tetrahydroimidazole-substituted Methylene β-Diketones

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