Carbon permutation is protonated dimethylfurans

Audier, H. E.; Robin, D.

doi:10.1002/oms.1210220513

Cited by 8 publications

(8 citation statements)

References 5 publications

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“…Each point represents an average of at least three spectra averaged over an eluted peak; the filled triangle represents three points that coincide (within experimental uncertainty of 2%); the open square represents two points that coincide within experimental uncertainty; ×'s represent single points. The solid curve shows the best least-squares fit, and the dashed curves correspond to 95% confidence limits 1 Ion Intensity Ratios ( r = m/z 95/ m/z 94) from CAD of Molecular Ions (Selected with a 3 amu Window) of Deuterated sec -Alkyl Phenyl Ethers even ( n + m )[PhOD •+ ]/[PhOH •+ ]odd ( n + m )[PhOD •+ ]/[PhOH •+ ] phenoxybutanes phenoxyheptanes threo -2-PhO-3- d 1 0.435 (0.015) threo -2-PhO-3- d 1 0.55 (0.04) erythro -2-PhO-3- d 1 0.36 (0.02) erythro -2-PhO-3- d 1 0.21 (0.02) 2-PhO-1,1,1- d 3 0.13 (0.02) 2-PhO-1,1,1- d 3 0.12 (0.01) threo -3-PhO-2- d 1 0.37 (0.06) phenoxyoctanes erythro -3-PhO-2- d 1 0.21 (0.015) threo -2-PhO-3- d 1 1.34 (0.21) threo -3-PhO-4- d 1 0.355 (0.045) erythro -2-PhO-3- d 1 0.47 (0.11) erythro -3-PhO-4- d 1 0.14 (0.04) threo -3-PhO-2- d 1 0.66 (0.33) 3-PhO-3- d 1 <0.05 erythro -3-PhO-2- d 1 0.39 (0.14) threo -4-PhO-3- d 1 0.39 (0.03) 3-PhO-2,2,4,4- d 4 >20 erythro -4-PhO-3- d 1 0.14 (0.04) a Standard deviations (in parentheses) represent averages of single spectra (each one corresponding to the m/z 95 ion intensity maximum) recorded on at least three separate days.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Stereochemical Analysis of Monodeuterated Isomers By GC/MS/MS

et al. 1997

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GC/MS/MS techniques to quantitate mixtures of acyclic stereoisomers are explored for a set of secondary n-alkyl phenyl ethers vicinally substituted with deuterium. Examination of a set of test compounds using a commercial quadrupole ion trap instrument (GC/QIT) reveals large differences between threo and erythro diastereomers when trapped molecular ions expel neutral alkene as a result of collisionally activated dissociation (CAD). All of the monodeuterated compounds give PhOH•+ (m/z 94) and PhOD•+ (m/z 95) as the principal fragments under GC/QIT/CAD conditions. The threo isomers give consistently larger values of the ion intensity ratio r = m/z 95/m/z 94 than do the corresponding erythro, with a ratio of ratios r t /r e as high as 3. A nonlinear calibration curve shows that the threo decomposes to a lesser extent than the erythro in mixtures of the two stereoisomers; hence, the precision of quantitation is sensitive to experimental error. Sustained off-resonance irradiation experiments in an FT-ICR give virtually complete dissociation, which results in a linear calibration curve. Ion−molecule reactions of the fragment ions indicate that alkene expulsion does not take place via a six-member cyclic transition state, while the stereochemical selectivity appears to rule out the intermediacy of ion−neutral complexes. Threo- and erythro-2-phenoxy-3-deuterio-n-octane (and their mixtures) are proposed as test compounds for evaluating the capability of GC/MS/MS instrumentation to perform stereochemical analyses on subnanomole samples of isotopically labeled molecules.

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…”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Stereochemical Analysis of Monodeuterated Isomers By GC/MS/MS

et al. 1997

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“…4(E) and (F)). In principle, [5] (Fig. 2(B)), but the barriers for these reactions are much higher than those for the ring expansions (Fig.…”

Section: Isomerization Of 2-methylfuran Molecular Ionmentioning

confidence: 96%

“…In the present work, the B3LYP/6-311G++(3df,3pd)//B3LYP/6-31G(d,p) level is used to study the reaction mechanisms for the mutual interconversions of the ions [C 5 …”

Section: Scheme 1 Preliminary Proposed Reaction Mechanisms For the Fmentioning

confidence: 99%

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Density functional theory and RRKM calculations of the gas‐phase unimolecular rearrangements of methylfuran and pyran ions before fragmentations

Espinoza¹,

Narváez²

2009

J. Mass Spectrom.

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The potential energy profiles for the mutual conversion of the isomeric molecular ions [C5H6O]+* of 2-methylfuran, 3-methylfuran and 4H-pyran and the fragmentations that lead to [C(5)H(5)O](+) ions were obtained from calculations at the B3LYP/6-311G++(3df,3pd)//B3LYP/6-31G(d,p) level of theory. The various competing unimolecular processes were characterized by their RRKM microcanonical rate coefficients, k(E), using the sets of reactant and transition state frequencies and the kinetic barriers obtained from the density functional method. In either a high- or a low-energy regime, the pyrylium ion [C5H5O]+ is generated directly from the 4H-pyran molecular ion by a simple cleavage. In contrast, in the metastable kinetic window, the molecular ions of methylfurans irreversibly isomerize to a mixture of interconverting structures before dissociation, which includes the 2H- and 3H-pyran ions. The hydrogen atoms attached to saturated carbons of the pyran rings are very stabilizing at the position 2, but they are very labile at position 3 and can be shifted to adjacent positions. Once 4H-pyran ion has been formed, the C-H bond cleavage begins before any hydrogen shift occurs. According to our calculation, there would not be complete H scrambling preceding the dissociation of the molecular ions [C5H6O]+*. On the other hand, as the internal energy of the 2-methylfuran molecular ion increases, H* loss can become more important. These results agree with the available experimental data.

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Density functional theory and RRKM calculations of decompositions of the metastable E‐2,4‐pentadienal molecular ions

Espinoza

Narváez

2010

J. Mass Spectrom.

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The potential energy profiles for the fragmentations that lead to [C(5)H(5)O](+) and [C(4)H(6)](+*) ions from the molecular ions [C(5)H(6)O](+*) of E-2,4-pentadienal were obtained from calculations at the UB3LYP/6-311G + + (3df,3pd)//UB3LYP/6-31G(d,p) level of theory. Kinetic barriers and harmonic frequencies obtained by the density functional method were then employed in Rice-Ramsperger-Kassel-Marcus calculations of individual rate coefficients for a large number of reaction steps. The pre-equilibrium and rate-controlling step approximations were applied to different regions of the complex potential energy surface, allowing the overall rate of decomposition to be calculated and discriminated between three rival pathways: C-H bond cleavage, decarbonylation and cyclization. These processes should have to compete for an equilibrated mixture of four conformers of the E-2,4-pentadienal ions. The direct dissociation, however, can only become important in the high-energy regime. In contrast, loss of CO and cyclization are observable processes in the metastable kinetic window. The former involves a slow 1,2-hydrogen shift from the carbonyl group that is immediately followed by the formation of an ion-neutral complex which, in turn, decomposes rapidly to the s-trans-1,3-butadiene ion [C(4)H(6)](+*). The predominating metastable channel is the second one, that is, a multi-step ring closure which starts with a rate-limiting cis-trans isomerization. This process yields a mixture of interconverting pyran ions that dissociates to the pyrylium ions [C(5)H(5)O](+). These results can be used to rationalize the CID mass spectrum of E-2,4-pentadienal in a low-energy regime.

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Carbon permutation is protonated dimethylfurans

Cited by 8 publications

References 5 publications

Stereochemical Analysis of Monodeuterated Isomers By GC/MS/MS

Stereochemical Analysis of Monodeuterated Isomers By GC/MS/MS

Density functional theory and RRKM calculations of the gas‐phase unimolecular rearrangements of methylfuran and pyran ions before fragmentations

Density functional theory and RRKM calculations of decompositions of the metastable E‐2,4‐pentadienal molecular ions

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