Free Radicals by Mass Spectrometry. XLV. Ionization Potentials and Heats of Formation of C3H3, C3H5, and C4H7 Radicals and Ions

Lossing, F. P.

doi:10.1139/v72-629

Cited by 215 publications

(53 citation statements)

References 28 publications

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“…It has been shown by experiment [9] and theory [10,11] that the aromatic cyclopropenyl cation and the aliphatic propagyl cation are the most stable C 3 H 3 isomers. Therefore, the dissociation pathways depicted in Scheme 3 are proposed for the loss of CO and CS from 3 a,b and 4 a,b, respectively, by which the corresponding C 3 H 3 CO and C 3 H 3 CS ions (3 c,d and 4 c,d, respectively) are formed.…”

Section: Resultsmentioning

confidence: 99%

Locating the Charge Site in Heteroaromatic Cations

et al. 1998

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Low-energy collision-induced dissociation (CID) and ion ± molecule reactions with 2-methyl-1,3-dioxolane (MD) performed by pentaquadrupole (QqQqQ) mass spectrometry were applied to locate the charge site in isomeric heteroaromatic cations. The 2-, 3-, and 4-pyridyl cations are indistinguishable by CID. However, as suggested by MS 3 experiments and ab initio calculations, the 2-pyridyl cation reacts extensively with MD by a transacetalization-like mechanism to afford a bicyclic dihydrooxazolopyridyl cation. The 3-and 4-pyridyl cations, on the contrary, react predominantly with MD by proton transfer, as does the analogous phenyl cation. The 2-, 4-, and 5-pyrimidyl cations display characteristic CID behavior. In addition, the 2-pyrimidyl cation reacts extensively with MD by the transacetalization-like mechanism, whereas proton transfer occurs predominantly for the 4-and 5-pyrimidyl cations. The ions thought to be the 2-and 3-furanyl and 2-and 3-thiophenyl cations show indistinguishable CID and ion ± molecule behavior. This is most likely the result of their inherent instability in the gas phase and their spontaneous isomerization to the corresponding butynoyl and butynethioyl cations HCCHCH 2 CO and HC CHCH 2 C S . These isomerizations, which are considerably exothermic according to G2(MP2) ab initio calculations, are indicated by a series of experimental results. The ions dissociate upon CID by loss of CO or CS and undergo transacetalization with MD. Most informative is the participation of HC CHCH 2 C S in a transacetalization/dissociation sequence with replacement of sulfur by oxygen, which is structurally diagnostic for thioacylium ions. It is therefore possible to locate the charge site of the 2-pyridyl and the three 2-, 4-, and 5-pyrimidyl cations and to identify the isomeric precursors from which they are derived. However, rapid isomerization to the common HCCH-CH 2 -CO(S) ion eliminates characteristic chemical behavior that could result from different charge locations in the heteroaromatic 2-and 3-furanyl and 2-and 3-thiophenyl cations.

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Section: Resultsmentioning

confidence: 99%

Locating the Charge Site in Heteroaromatic Cations

et al. 1998

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“…It was a very broad signal of Gaussian shape, T0.,-640 meV. This reaction has its counterpart in the fragmentations of propene and cyclopropane' where the proposed reaction sequence was elimination of H2 followed by loss of H: For the C4Hs molecules the consecutive reactions can be either (l), then (7), or (2) followed by (8):…”

Section: Molecular Ion Fragmentationsmentioning

confidence: 94%

“…where at threshold, the daughter ion is known to have the ally1 structure. 8 The authors concluded that the effect of increasing the ionizing electron energy, namely a decrease in both 13C and *H randomization, could adequately be explained by a skeletal isomerization involving a series of 1,3 ring closures to form methylcyclopropane type ions. In contrast, however, they observed that molecular ions yielding C2 fragment ions apparently had undergone total carbon randomization prior to decomposition at all electron energies.…”

Section: Introductionmentioning

confidence: 99%

Metastable ion studies. IX—Thermochemistry and ion structures among fragmentating ions, an electron impact and field ionization investigation

Holmes

Weese

Blair

et al. 1977

Org. Mass Spectrom.

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“…(5). The ionization energy of DMCP, 9.08eV (12), is below the photoenergy of the krypton (10.0eV) resonance radiation. The ionization efficiency for DMCP was determined at 123.6 nm and found to be q = 0.10.…”

Section: Introductionmentioning

confidence: 90%

Vacuum-ultraviolet (147.0 nm and 123.6 nm) photolysis of 1,1-dimethylcyclopropane

Binkewicz¹,

Kaplan²,

Doepker³

1981

Can. J. Chem.

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. Can. J. Chem. 59,537 (1981). The gas-phase photolysis of 1,l-dimethylcyclopropane has been investigated using xenon (147.0nm) and krypton (123.6nm) resonance radiation. Major products observed in order of decreasing importance were isobutene, ethylene, hydrogen, 1,3-butadiene 2-methyl-1,3-butadiene, propylene, allene, methylacetylene, and acetylene. Radical scavengers, NO and 0 2 , and radical interceptors, H2S/D2S and HI, were used to determine the relative importance of radical and molecular processes. CH,, C2H3, C,H,, and C,H7 radical species were identified and quantified. Ten primary reaction channels were postulated, of which the elimination of methylene was the most predominant, accounting for 34% of the photo-decomposition at 147.0nm and 39% at 123.6 nm. Although ionization was established at 123.6 nm (q = 0.10) the nature of a charge transfer or other ion-molecule reaction channel leading to the formation of 2-methyl-1-butene and 2-methyl-2-butene could not be determined. On aetudie laphotolyse en phase gazeuse du dimethyl-I, 1 cyclopropane en utilisant la radiation de resonance du xenon (147,O nm) et du krypton (123,6nm). Les principaux produits observes sont par ordre decroissant d'importance: l'isobutene, I'ethykne, I'hydrogene, le butadiene-1,3 le methyl-2 butadikne-1.3, le propkne, I'allkne, le propyne et I'acetylene. On a utilise les pibges a radicaux NO et 0, et les intercepteurs de radicaux H2S/D2S et HI pour determiner I'importance relative des processus radicalaire e t molkulaire. On a identifie et quantifit les espbces radicalaires CH3, C2H3, C3H, et C4H7. On postule la presence de dix chemins reactionnels primaires dans lesquels I'elimination de m e t h y h e predomine; cette elimination correspond a 34% lors de la photod~composition a 147,O nm et de 39% a 123,6 nm. Bien qu'on ait etabli la presence d'ionisation a 123,6 nm (q = 0, lo), on ne peut pas determiner la nature d'un processus de transfert de charge ou d'une autre reaction ion-molCcule conduisant a la formation du methyl-2 butbne-l et du methyl-2 butkne-2.[Traduit par le journal]

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Free Radicals by Mass Spectrometry. XLV. Ionization Potentials and Heats of Formation of C₃H₃, C₃H₅, and C₄H₇ Radicals and Ions

Cited by 215 publications

References 28 publications

Locating the Charge Site in Heteroaromatic Cations

Locating the Charge Site in Heteroaromatic Cations

Metastable ion studies. IX—Thermochemistry and ion structures among fragmentating ions, an electron impact and field ionization investigation

Vacuum-ultraviolet (147.0 nm and 123.6 nm) photolysis of 1,1-dimethylcyclopropane

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