An unexpected γ‐hydrogen rearrangement in the mass spectra of di‐<i>ortho</i> ‐substituted alkylbenzenes

Kingston, Eric E.; Eichholzer, John V.; Lyndon, Paul; MacLeod, John K.; Summons, Roger E.

doi:10.1002/oms.1210230108

Cited by 22 publications

(5 citation statements)

References 13 publications

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“…8 Moreover, classic mass spectrometry literature showed that this rearrangement does not occur if the ortho positions of the phenyl ring or the γ carbon atoms are completely substituted. 43 This mechanism is proposed to explain the formation of DII and HI ions observed in sec-PD 8 S-H SIMS spectra. Indeed most of the odd peaks (HI) present in the sec-PD 8 S-H SIMS spectra can be explained through this rearrangement mechanism (Scheme 3).…”

Section: Discussionmentioning

confidence: 97%

Molecular Weight Dependent Fragmentation of Selectively Deuterated Polystyrenes in ToF−SIMS

1999

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Two series of monodisperse polystyrenes were synthesized by an anionic polymerization initiated with sec-butyllithium. The number average molecular weights of the macrochains range from 1700 to 93300. The first series consist of deuterated repeat units and hydrogenated end groups (sec-PD8S−H). The other one was fully hydrogenated except for one end group, which was selectively deuterated (sec-PS−D). The sample molecular structures are C4H9(C8D8) n H and C4H9(C8H8) n D, respectively. These polymers were then analyzed by time-of-flight secondary ion mass spectrometry (ToF−SIMS). All secondary ion intensities are corrected for the carbon and deuterium isotopic distributions. Static SIMS spectra of sec-PD8S−H show characteristic peaks with even masses (fully deuterated, i.e., C7D7 +, C6D5 + at m/z = 98, 82) and odd peaks (containing at least one hydrogen atom, i.e., C7HD6 +, C6HD4 + at m/z = 97, 81). Typically, these odd peaks show decreasing intensities as the molecular weight increases. In the sec-PS−D SIMS spectra, the characteristic peaks are similar to those observed for the usual polystyrene with a more specific peak at m/z = 92 which is related to the deuterium end group. From the molecular weight dependent intensities, it can be deduced that a hydrogen transfer occurs from the sec-butyl end group to the first repeat unit and promotes the formation of the tropylium fragment. A rearrangement ion formation mechanism is proposed. For both polymers, characteristic peaks of the end group are detected. With the intensity ratios of a main chain fragment and these end groups characteristic peaks, we are able to calibrate the number average molecular weight at the polymer surface. Moreover, it is shown that the main chain deuteration influences the end group segregation toward the surface.

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Section: Discussionmentioning

confidence: 97%

Molecular Weight Dependent Fragmentation of Selectively Deuterated Polystyrenes in ToF−SIMS

1999

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“…This is due to the absence of methyl group C-19', so that the y-hydrogen atom is attached to a secondary instead of a tertiary carbon atom, favouring the McLafferty rearrangement in isorenieratane and the C33 diaryl isoprenoid (cf. Kingston et al, 1988;Sinninghe Damst6 et al, 1988a). …”

Section: C~2 and C3~ Compoundsmentioning

confidence: 99%

Diagenetic and catagenetic products of isorenieratene: Molecular indicators for photic zone anoxia

Koopmans

Köster

Kaam-Peters

et al. 1996

Geochimica et Cosmochimica Acta

368

152

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Abstract--A wide range of novel diagenetic and catagenetic products of the diaromatic carotenoid isorenieratene, a pigment of the photosynthetic green sulphur bacteria Chlorobiaceae, has been identified in a number of sedimentary rocks ranging from Ordovician to Miocene. Compound identification is based on NMR, mass spectrometry, the presence of atropisomers, and stable carbon isotopes. Atropisomers contain an axially chiral centre which, in combination with other chiral centres, results in two or more diastereomers that can be separated on a normal GC column. Chlorobiaceae use the reverse TCA cycle to fix carbon, so that their biomass is enriched in 13C. High ~3C contents of isorenieratene derivatives therefore support their inferred origins.Isorenieratene derivatives include C4o, C33, and C32, diaryl isoprenoids and short-chain aryl isoprenoids with additional aromatic and/or S-containing rings. C33 and C32 compounds are diagenetic products of C33 and C32 "carotenoids" formed from isorenieratene during early diagenesis through expulsion of toluene and m-xylene, respectively. Cyclisation of the polyene acyclic isoprenoid chain can proceed via an intramolecular Diels-Alder reaction, followed by aromatisation of the newly formed ring. Sulphurisation is also an important process during early diagenesis, competing with expulsion and cyclisation. Sulphur-bound isorenieratane is released during progressive diagenesis, due to cleavage of relatively weak S-S and C-S bonds. Cleavage of C-C bonds during aromatisation of newly formed rings and during catagenesis yields short-chain compounds. The inherent presence of a conjugated double bond system in carotenoids implies that similar diagenetic and catagenetic reactions can occur with all carotenoids.Chlorobiaceae live at or below the oxic/anoxic boundary layer and require both light and H2S. The presence of isorenieratene or its diagenetic and catagenetic products in ancient sedimentary rocks and crude oils is therefore an excellent indication for photic zone anoxia in the depositional environment. Diagenetic and catagenetic products of isorenieratene are expected to find applications in reconstruction of palaeoenvironments and in oil-oil and oil-source rock correlation studies. Their presence in several petroleum source rocks suggests that anoxia is an important environmental parameter for the preservation of organic matter.

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“…Mass spectra of low-molecular-weight alkylbenzenes have been reported [24,25]. The base peak for most alkylated alkylbenzenes results from cleavage of the benzylic bond and loss of the largest alkyl substituent.…”

Section: Retention Index Measurementsmentioning

confidence: 99%

Identification of C2C4 alkylated benzenes in flash pyrolysates of kerogens, coals and asphaltenes

Hartgers

Damsté

Leeuw

1992

Journal of Chromatography A

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Pseudo-Kovats indices were determined for all positional isomers of Ca-C, alkylated benzenes using a non-polar capillary column (CP Sil-5). These indices were applied in combination with mass spectral data to identify these compounds in complex mixtures of a relatively non-polar nature generated upon flash pyrolysis of macromolecular sedimentary organic matter (kerogens, asphaltenes and coals). Alkylbenzene distribution patterns were constructed by integration of appropriate mass chromatograms. Generally, toluene is the major pyrolysis product. Other specific alkylated benzenes (e.g. 1,2,3,4_tetramethylbenzeneand I-methyl-4-isopropylbenzene) were found to be enhanced in flash pyrolysates of different samples. Flash pyrolysates of asphaltene and kerogen fractions isolated from the same oil shale exhibit similar alkylbenzene distributions.1NTRODUCTlON

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An unexpected γ‐hydrogen rearrangement in the mass spectra of di‐ortho ‐substituted alkylbenzenes

Cited by 22 publications

References 13 publications

Molecular Weight Dependent Fragmentation of Selectively Deuterated Polystyrenes in ToF−SIMS

Molecular Weight Dependent Fragmentation of Selectively Deuterated Polystyrenes in ToF−SIMS

Diagenetic and catagenetic products of isorenieratene: Molecular indicators for photic zone anoxia

Identification of C2C4 alkylated benzenes in flash pyrolysates of kerogens, coals and asphaltenes

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