Mass spectral studies of naphthoflavones

The electron impact induced fragmentations of the five possible naphthoflavones have been studied with the aid of low- and high-resolution measurements, metastable decompositions and isotope labelling using either deuterium or carbon-13 atoms. All compounds show both the direct expulsion of a CO residue from the carbonyl group and the retro Diels–Alder cleavage. The abundant [M–H]⁺ ion has been formulated as the substituted β-tropolone species, which, in the case of β-naphthoflavone, is in competition with a pentacyclic species arising from the elimination of H-5 as evidenced in the spectrum of 5-d-β-naphthoflavone. Other previously unsuspected ions are also in evidence.     

Mass spectral studies on tanshinones

The mass spectra of three groups of tanshinones have been examined and a number of characteristic features noted which might be helpful in the micro-identification of the natural products. The fragmentation patterns are similar to each other except for the relative intensity within the same group of tanshinones and are accounted for in terms of the general fragmentations of furans and quinones. Characteristic ions at m/e 178, 165 and 152 found in all kinds of tanshinones may be considered to be of highly aromatized hydrocarbon fragments and are of good for the structure elucidation of these compounds.     

Mass spectral studies of some carbohydrate enones

A study of the mass spectra of ethyl 2,3-dideoxy-α-d-glycero-hex-2-enopyranosid-4-ulose1a, its 6-0-acetyl derivative1b, and methyl 3,4-dideoxy-α-d-glycero-hex-3-enopyranosidulose2a indicates that the main fragmentation of these compounds occurs by a retro-Diels-Alder type cleavage. Recognition of the ions produced by this cleavage provides a means of allocating the position of the α,β-unsaturated chromophore in carbohydrate enones. Fragmentation of molecular ions of1a and1b also occurred by direct loss of individual ring substituents to give ions which retain the pyranoid nucleus. The fragmentation pathways suggested are supported by accurate mass measurements of the salient fragment ions of1a.     

Mass spectral studies on thiobenzoates and thioacetates

The mass spectra of O-methyl and O-ethyl thiobenzoates and their derivatives have been recorded together with those of the corresponding S-alkyl thiobenzoates. The direct fragmentations of the O-alkyl thiobenzoates are almost identical to those of alkyl benzoates and of S-alkyl thio-benzoates. Several important differences in rearrangements upon electron-impact can be observed between them, however. These are the migration of the alkyl group from the alkoxy oxygen to the thiocarbonyl sulphur and the migration of a hydrogen from the alkoxy group to the thiocarbonyl group. O-methyl and O-ethyl thioacetates behave similarly. The mass spectra of the thioesters obtained with low electron-accelerating voltages have also been studied.     

Mass spectral studies of native and mass-labeled perfluorooctanesulfonamides

This work examines the mass spectra of several environmentally relevant amides, perfluorooctanesulfonamide (FOSA), NMeFOSA, NEtFOSA, and NMe(2)FOSA, under electron ionization conditions. A previous mass spectral study of FOSA and NEtFOSA led the authors to propose possible structures for some of the fragment ions and fragmentation pathways that might explain their formation. In the present communication, further fragment ions are identified for these two compounds and alternative fragmentation pathways proposed. Mass spectral analyses of NMeFOSA and NMe(2)FOSA and of mass-labeled NMeFOSA and NEtFOSA reinforce our conclusions about potential fragmentation pathways for these amides and the fragment ions expected. The mass spectral data presented here will help chemists to identify signals found in a gas chromatographic/mass spectrometric (GC/MS) analysis that stem from these perfluoroalkylsulfonamides.     

Mass spectral and NMR studies of some cinnolines

Fragmentation upon electron impact of cinnoline (1) occurs with the consecutive loss of N₂ and C₂H₂. Fragmentation of 4,4′-dicinnolyl (2) and 4-styrylcinnoline (4) gives a series of ions leading to the “dibenzoladderene” ion (3) and the 1-phenylbenzodibutylene ion (5) respectively. Fragmentation of 4-styrylquinoline (6) also leads to 5 , but of more interest is the loss of H. during ring rearrangement to give the highly resonance stabilized 3-styrylbenzocyclo-pentadieneoneimine ion (7) which then loses N. Fragmentation of various other substituted cinnolines follow different pathways: 4-methylcinnoline (8) apparently fragments through the “1,2-diazatropylium” ion (9) ; nitrocinnolines fragment with initial loss of the nitro substituent; aminocinnolines fragment with initial loss of N₂; and 4-cinnolone (17) fragments with the consecutive loss of two HCN's and CO. The NMR spectra of cinnolines generally show the following order of deshielding: 3-proton > 8-proton > 4-proton. The spectra of cinnolinum chloride (18) is interpreted in terms of protonation at N-1 of 1 , and the spectrum of 17 is interpreted in terms of strong intermolecular hydrogen bonding.     

Mass spectral studies of a series of N,N-dialkyl aminoethyl-2-chlorides and trimethyl silyl ethers of N,N-dialkyl aminoethane-2-ols under electron impact conditions

The electron impact (EI) mass spectra of a series of N,N-dialkyl-aminoethyl-2-chlorides, N(R(1))(R(2))-CH(2)-CH(2)Cl and trimethylsilyl ethers of N,N-dialkyl aminoethane-2-ols, N(R(1))(R(2))-CH(2)-CH(2)-O-Si(CH(3))(3), where R(1) and R(2) = methyl, ethyl, propyl and isopropyl, which are precursors of VX type of compounds, are studied. All the compounds (1-20) show abundant molecular ions, in addition to a weak [M - H](+) ion, except the N,N-diisopropyl group containing compounds (8 and 18). A general EI fragmentation pattern for the above two series of compounds is discussed. The observed fragment ions are due to simple homolytic cleavages, and they are distinct to allow the identification of the compounds unequivocally including those of isomeric compounds. The primary fragmentation of compounds 1-20 is beta-cleavage, i.e. homolytic cleavage of C-C bond, which is linked to the nitrogen atom. Three types of beta-cleavages are possible for these compounds, in which the abundance of beta-cleavage product ions is found to depend on the size and structure of the alkyl group attached to nitrogen. The alpha-cleavage fragment ions are found only for N,N-dialkyl aminoethyl-2-chlorides but are absent in the corresponding trimethylsilyl ethers of N,N-dialkyl aminoethane-2-ols. The retention indices are calculated for all the studied compounds (1-20) and are in the ranges of 750.38-1079.24 for 1-10 and 905.23-1190.25 for 11-20.     

Electrospray ionization mass spectral studies of N,N-dialkylaminoethane-2-sulphonic acids

Oxidative reactions of VX type compounds and N,N-dialkylaminoethane-2-thiols that are precursors for VX compounds produce N,N-dialkylaminoethane-2-sulphonic acids, N(R(1))(R(2))-CH(2)-CH(2)SO(3)H (where R(1) and R(2) = methyl, ethyl, n-propyl and isopropyl, 1-10), as the degradation products, and these degradation products are considered as markers for the detection of chemicals listed in the schedules of Chemical Weapons Convention (CWC) chemicals. Off-site detection of such degradation products in aqueous samples is an important task in the verification of CWC-related chemicals. Here we report a simple method involving the direct analysis of aqueous samples using positive and/or negative ion electrospray ionization (ESI) for the screening, detection and identification of N,N-dialkylaminoethane-2-sulphonic acids, avoiding sample preparation and chromatographic steps. The positive ion ESI mass spectra of all the compounds result in abundant [M+Na](+) ions, and the negative ion spectra show abundant [M-H](-) ions to confirm their molecular weight. The collision-induced dissociation spectra of [M+Na](+) and [M-H](-) give characteristic product ions by which it is easy to detect and identify all the studied N,N-dialkylaminoethane-2-sulphonic acids including those of isomeric compounds. The method is successfully applied to detect the spiked chemical, N,N-diisopropylaminoethane-2-sulphonic acid, present in a water sample received in a proficiency test.     

Mass spectral fragmentation studies in monomeric and dimeric coumarins

A study on the behavior of a large number of monomeric and dimeric coumarins in the mass spectrometer is reported and discussed. The results illustrate that the observed characteristic fragmentation patterns are of considerable utility in the application of mass spectrometry to structure elucidation in this series.     

Mass spectral study on O,O-dialkyl N,N-dialkyl phosphoramidates under electron impact conditions

A series of O,O-dialkyl N,N-dialkyl phosphoramidates (1-25) were analyzed under GC-EIMS conditions. Clear-cut differences are found in the fragmentation of O,O-dialkyl N,N-dimethyl phosphoramidates (Series 1) and O,O-dimethyl N,N-dialkyl phosphoramidates (Series 2). The phosphoramidates comprising of mixed/crossed alkyl groups on nitrogen and oxygen (Series 3) showed mixed fragmentation pattern corresponding to both Series 1 and 2 depending on the nature of alkyl groups. All the possible isomers among the studied compounds showed distinguishable EI mass spectra. Although the major ions in the EI mass spectra for the isomers containing O-n-propyl or O-isopropyl and N,N-diethyl or N-isopropyl N-methyl are similar, the isomers could be distinguished by characteristic ions of low abundance at low mass region. The differences are prominent in the metastable ion spectra of characteristic ions.     

Mass spectral studies of some fructose containing oligosaccharide permethyl ethers

Mass spectrometry can be used to characterise fructofuranose units connected via C₂ to another sugar. The intensity of the m/e 101 and m/e 88 ions cannot be used to differentiate between furanose and pyranose ring forms in disaccharide permethyl ethers. The type of glycosidic linkage has considerable influence on the formation of these ions.