Ion-neutral complexes as intermediates in the decompositions of C5H10O2.cntdot.+ isomers

McAdoo, David J.; Hudson, Charles E.; Skyiepal, M.; Broido, Ellen M.; Griffin, Lawrence L.

doi:10.1021/ja00259a012

Cited by 38 publications

(10 citation statements)

References 2 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…3), the corresponding [CH 3 CO] + ion (m/z 43) appears with a higher intensity in the EI spectra; this result shows that the ion of m/z 43 comes partly from a straightward bond rupture. In the gas phase, product ions from the cleavage of covalent bonds do not always lead to prompt separation; often the charged and neutral cleavage products remain held together by ion/dipole or ion/induced dipole attraction for a time sufficient for them to undergo ion/molecule reactions.…”

Section: Fragmentation Of the Ion Of M/z 153mentioning

confidence: 86%

“…This means that the ion/neutral complex is a reactive intermediate. In this complex, the hydrogen transfer from [CH 3 CO] + ion to a neutral fragment to form an ion of m/z 111, in a rearrangement process (Scheme 1), requires less energy than simple bond cleavage. Under the circumstances of their coexistence in intermediates having a range of internal energies, both the direct rupture ion of m/z 43 and the rearrangement ion of m/z 111 seen in the CID spectrum of the ion of m/z 153 will be formed by competing mechanisms (Scheme 1).…”

Section: Fragmentation Of the Ion Of M/z 153mentioning

confidence: 99%

“…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.…”

mentioning

confidence: 99%

See 2 more Smart Citations

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

She

Liu

1997

Rapid Commun. Mass Spectrom.

View full text Add to dashboard Cite

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...

show abstract

Section: Fragmentation Of the Ion Of M/z 153mentioning

confidence: 86%

Section: Fragmentation Of the Ion Of M/z 153mentioning

confidence: 99%

See 1 more Smart Citation

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

She

Liu

1997

Rapid Commun. Mass Spectrom.

View full text Add to dashboard Cite

show abstract

“…[26] In MS of small molecules McLafferty þ 1 rearrangements are supposed to occur in a charge-induced mechanism. For polymer fragmentation in general and for PEG ionized with sodium in particular, usually a charge-remote mechanism is assumed as ionization of the chains happens in general via the attachment of an ion.…”

Section: Tosylated Mpegmentioning

confidence: 99%

Systematic MALDI‐TOF CID Investigation on Different Substituted mPEG 2000

Knop

Jahn

Hager

et al. 2010

Macro Chemistry & Physics

View full text Add to dashboard Cite

Methoxy poly(ethylene glycol) 2000 (mPEG 2000) samples were substituted via esterification reactions to convert the hydroxyl end group of the mPEG into potential initiators for the cationic ring opening polymerization of 2‐oxazolines. These substitution products were investigated by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS); in addition, detailed MALDI‐TOF/TOF‐collision induced dissociation (CID) MS studies were performed to introduce this method as complementary structural characterization tool allowing the detailed analysis of the prepared macromolecules. The CID of the macroinitiators revealed 1,4‐hydrogen and 1,4‐ethylene eliminations forming very regular fragmentation patterns which showed, depending on the end groups, different fragmentation series. Furthermore, very pronounced McLafferty + 1 rearrangements (1,5 hydrogen‐transfer) of the introduced ester end groups were observed leaving the mPEG molecule as neutral acid. This incisive loss revealed the exact molar mass for each end group and, therefore, represents an important tool for end group determination of functionalized polymers.magnified image

show abstract

“…However, these hypotheses have not been confirmed by 13C labelling and the fragmentation pathways leading to the fragment ions have not been established except for [4 -C2H,]+.. '5 In this study we report a comparison of the massanalysed ion kinetic energy (MIKE) spectra of ions 4, 5, 7 Under collision conditions, these fragment ions, formed in the source or in the first field-free region (FFR) by fragmentatiion of 4, 5, 7 and 8, give identical MIKE collision-induced dissociation (CID) spectra corresponding to protonated 3-penten-2-one. The lone enolic precursor leading to such a fragment is 7a.…”

mentioning

confidence: 96%

Competitive isomerization processes of 5‐methyl‐2‐hexanone radical cations

Audier

Denhez

Mourgues

1989

Rapid Comm Mass Spectrometry

View full text Add to dashboard Cite

A great number of isomerization reactions occur before dissociation of metastable [C,H2,+,COR]+' radical cations (R = OH, CH3, C6H,, n = 4,5). These processes are often identical for carboxylic acids and ketones. For instance, it -has been shown that pentanoic acid radical cations isomerize: (i) by 1-2',2, 1-3 and 1-43-9 CH202 migration, respectively, into the 0, y and 6 distonic ions (Scheme 1, mechanisms (a), (b) and (c)), and (ii) by rearrangement of the y distonic ion either through a cyclopropanoic transition state3 or through an [enol-alkene]+' ion/molecule ~o m p l e x~,~ leading to reversible isomerization of n-pentyl ion into isopentyl ion (mechanism (d)).The same processes have been observed for the metastable 2-hexanone radical cation". ' I . Rearrange- A comprehensive study of labelled n-hexanoic acid radical shows that these ions undergo fewer skeletal rearrangement processes than pentanoic acid radical cations.Two transposition reactions have been proposed for [CH,COC,H,,]+' ions: (i) l e 2 4 313 (Scheme 2) involving the mechanism (c) (Scheme l ) , and (ii) 5c34-,614.15 (Scheme 2) involving, in the first step, mechanism (d) and in the second step mechanism (b).However, these hypotheses have not been confirmed by 13C labelling and the fragmentation pathways leading to the fragment ions have not been established except for [4 -C2H,]+.. '5 In this study we report a comparison of the massanalysed ion kinetic energy (MIKE) spectra of ions 4, 5, 7 and 8 which allows the elucidation of the origin of the main fragment [M -C2Hs]+, the confirmation of the reversible isomerization of 4 into 5 and the evidencing of other rearrangements. Scheme 2

show abstract

Ion-neutral complexes as intermediates in the decompositions of C5H10O2.cntdot.+ isomers

Cited by 38 publications

References 2 publications

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

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

Systematic MALDI‐TOF CID Investigation on Different Substituted mPEG 2000

Competitive isomerization processes of 5‐methyl‐2‐hexanone radical cations

Contact Info

Product

Resources

About