Mass spectrometric studies of structural isomers—II: Mono‐and bicyclic C<sub>6</sub>H<sub>10</sub> molecules

Winters, Robert E.; Collins, Jerome H.

doi:10.1002/oms.1210020308

Cited by 23 publications

(36 citation statements)

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“…The reason for this discrepancy lies probably in a wrong calibration of the energy scale, since the cyclohexene ionization energy is itself overestimated by ∼0.6 eV in Praet's report. 18 More recently, Li and Baer 20 explored the behavior of cyclohexene by threshold photoelectron-photoion coincidence spectroscopy; they obtained AE values for both [C 5 H 7 ] + and [C 4 H 6 ] •+ within ∼0.1 eV of the results reported by Winters and Collins 17 and Traeger and Lossing. 19 It is essential to note that the differences between the appearance and ionization energies for methyl loss and ethylene loss, 119 17 -127 19 and 166 17 kJ/mol, respectively, are close to the enthalpy difference between the dissociation products and the cyclohexene molecule (Table 1).…”

Section: Resultsmentioning

confidence: 74%

“…[17][18][19] As mentioned in the Introduction, methyl loss is the lowest energy pathway of the two competitive channels. Winters 17 By contrast, Praet, 18 who used the extrapolated voltage difference method, reported AE energies higher by ∼1.0 eV than the values reported by the preceding authors. The reason for this discrepancy lies probably in a wrong calibration of the energy scale, since the cyclohexene ionization energy is itself overestimated by ∼0.6 eV in Praet's report.…”

Section: Resultsmentioning

confidence: 99%

“…Again, appearance energy determinations point to the formation of the dissociation products close to their thermochemical threshold. 17,20 Information provided by the deuterium labeling indicates a preference for the elimination of C 2 H 4 containing the hydrogen atoms in positions 3 and 3′ at high internal energy, and a statistical distribution of the labels at low internal energy. This latter phenomenon has been suggested to originate from 1,3-allylic-hydrogen shifts on the intact cyclohexene ring.…”

Section: Introductionmentioning

confidence: 99%

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Low Energy Dissociation Processes of Ionized Cyclohexene: A Theoretical Insight^,

2004

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The major dissociation reactions of the cyclohexene radical cation, 1, lead to the cyclopentenyl ion by methyl loss and to ionized 1,3-butadiene after elimination of C 2 H 4 . These two reactions are also observed during the Diels-Alder reaction between ionized butadiene and ethylene in the gas phase. The energetic and mechanistic aspects of the methyl loss process from the cyclohexene radical cation or the reaction between ionized butadiene and ethylene are discussed with the help of molecular orbital calculations at the B3LYP/6-311+G(3df,2p)// B3LYP/6-31G(d) levels. Methyl loss is demonstrated to result from successive 1,2-hydrogen shifts and ringcontraction/ring-opening steps involving, as a crucial intermediate, ionized bicyclo[1,3,0]hexane rather than the distonic ion [CH 2 CH 2 CHCHCHCH 2 ] •+ (one of the open forms of ionized cyclohexene). This latter one is however involved during the direct and retro Diels-Alder reactions. The CH 3 and C 2 H 4 loss rate curves of the cyclohexene ion are calculated using the Rice-Ramsperger-Kassel-Marcus (RRKM) equation and the molecular orbital calculation results. These estimations allow understanding of the experimental observations concerning dissociations of the cyclohexene radical cation, 1, and the collision complex formed between ionized butadiene and ethylene.

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Section: Resultsmentioning

confidence: 74%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Low Energy Dissociation Processes of Ionized Cyclohexene: A Theoretical Insight^,

2004

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“…In the case of the AEs of the fragment ions investigated by EI technique, a considerable discrepancy was found. For example, the AE of C 3 H 5 + was determined to be 13.68 ± 0.05 eV by Praet, while Winters and Collins reported a value of 12.12 ± 0.12 eV . Recently, the near‐threshold absolute photoionization cross sections of cyclohexene was measured with photoionization mass spectrometry (PIMS) using a monochromated vacuum ultraviolet (VUV) synchrotron light source .…”

Section: Introductionmentioning

confidence: 99%

Vacuum ultraviolet photoionization mass spectrometric study of cyclohexene

et al. 2016

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In this work, photoionization and dissociation of cyclohexene have been studied by means of coupling a reflectron time-of-flight mass spectrometer with the tunable vacuum ultraviolet (VUV) synchrotron radiation. The adiabatic ionization energy of cyclohexene as well as the appearance energies of its fragment ions C6 H9 (+) , C6 H7 (+) , C5 H7 (+) , C5 H5 (+) , C4 H6 (+) , C4 H5 (+) , C3 H5 (+) and C3 H3 (+) were derived from the onset of the photoionization efficiency (PIE) curves. The optimized structures for the transition states and intermediates on the ground state potential energy surfaces related to photodissociation of cyclohexene were characterized at the ωB97X-D/6-31+g(d,p) level. The coupled cluster method, CCSD(T)/cc-pVTZ, was employed to calculate the corresponding energies with the zero-point energy corrections by the ωB97X-D/6-31+g(d,p) approach. Combining experimental and theoretical results, possible formation pathways of the fragment ions were proposed and discussed in detail. The retro-Cope rearrangement was found to play a crucial role in the formation of C4 H6 (+) , C4 H5 (+) and C3 H5 (+) . Intramolecular hydrogen migrations were observed as dominant processes in most of the fragmentation pathways of cyclohexene. The present research provides a clear picture of the photoionization and dissociation processes of cyclohexene in the 8- to 15.5-eV photon energy region.

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“…The thermochemistry of C6Hlo isomers has been investigated by Winters and Collins (22) and more recently by Lossing and Traeger (14). The latter authors conclusively showed that at threshold, the [C,M,]' daughter ion from cyclohexene has the [cy~lopentenium]~ structure; this they showed to be rhe most stable [C,H,]' ion, (AH, = 199 kcal mol-l) with [dimethylcyclopropenium] + as the probable nearest [C ,H7] ' isomer (AH,(estimated) = 217 kcal molF1).…”

Section: Introductionmentioning

confidence: 99%

Isomeric cyclic [C₆H₁₀]^+• ions. The energy barrier to ring opening

Wolkoff¹,

Holmes²

1979

Can. J. Chem.

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Appearance energies and metastable peak shapes for methyl loss from the molecular ions of cyclohexene, methylcyclopentenes, methylenecyclopentane, bicyclo[3.1.0]hexane, and 2-methyl-1,4-pentadiene indicate that they have a common reaction pathway which produces [cyclopentenium]+ as the daughter ion at threshold.From measurements of appearance energies and from relative peak abundances and kinetic energy releases for the metastable losses of CH3• and labelled methyl from the deuterium labelled cyclic [C6H10]+• molecular ions it was concluded that: (a) H/D mixing in [cyclohexene]+• occurs in the intact ring prior to a concerted methyl extrusion; (b) [methylcyclopentenes]+• loses methyl without any H/D mixing at or near to threshold by a straight C—C cleavage, possibly via the 3-isomer. Methyl losses involving H/D mixing are preceded by ring opening which has an activation energy of ca. 1 eV. However, [cyclopentenium]+• is again the daughter ion; (c) methylenecyclopentane and bicyclo[3.1.0]hexane molecular ions isomerize to methylcyclopentenes prior to methyl loss.H/D mixing (prior to methyl loss) in the molecular ion 1,1-2H2-2-methyl-1,4-pentadiene takes place before cyclisation to methylcyclopentene.

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Mass spectrometric studies of structural isomers—II: Mono‐and bicyclic C₆H₁₀ molecules

Cited by 23 publications

References 30 publications

Low Energy Dissociation Processes of Ionized Cyclohexene: A Theoretical Insight^,

Low Energy Dissociation Processes of Ionized Cyclohexene: A Theoretical Insight^,

Vacuum ultraviolet photoionization mass spectrometric study of cyclohexene

Isomeric cyclic [C₆H₁₀]^+• ions. The energy barrier to ring opening

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Mass spectrometric studies of structural isomers—II: Mono‐and bicyclic C6H10 molecules

Cited by 23 publications

References 30 publications

Low Energy Dissociation Processes of Ionized Cyclohexene: A Theoretical Insight,

Low Energy Dissociation Processes of Ionized Cyclohexene: A Theoretical Insight,

Vacuum ultraviolet photoionization mass spectrometric study of cyclohexene

Isomeric cyclic [C6H10]+• ions. The energy barrier to ring opening

Contact Info

Product

Resources

About

Mass spectrometric studies of structural isomers—II: Mono‐and bicyclic C₆H₁₀ molecules

Low Energy Dissociation Processes of Ionized Cyclohexene: A Theoretical Insight^,

Low Energy Dissociation Processes of Ionized Cyclohexene: A Theoretical Insight^,

Isomeric cyclic [C₆H₁₀]^+• ions. The energy barrier to ring opening