Electron impact studies—LXV: Negative-ion mass spectrometry of functional groups 2-aryl-1,3-dithianes

The negative-ion mass spectra of 2-aryl-1,3-dithianes contain pronounced molecular anions together with fragment ions which are produced by both simple and complex cleavage reactions. These spectra contain further examples of specific hydrogen scrambling processes in negative ions. Nitroaryldithianes give intense negative-ion spectra, and that of the o-nitro derivative exhibits an unusual proximity effect. The fragmentation patterns have been examined using both ²H and ¹³C labelling and the metastable defocusing technique.     

Electron-impact studies—XLVII: The mass spectra of 2-aryl-1,3-dithianes and -1,3-dithiolanes

The fragmentation patterns in the spectra of 2-aryl-1,3-dithianes and -1,3-dithiolanes have been elucidated by deuterium labelling studies. Ortho effects are observed in the spectra of 2(o-alkoxyphenyl)-1,3-dithianes. The molecular ions of the 1,3-dithianes eliminate S2H· and metastable kpeaks substantiate these eliminations. The hydrogen involved in this elimination randomises (C-4, 5 and 6) Prior to elimination in the spectrum of 2-phenyl-1,3-dithiane, but originates mainly from C-5 in that of the bis propane-1,3-dithioacetal of terephthaldehyde.     

Chemical ionization and electron impact mass spectra of alicyclic substituted 2-aryl-1,3-dithianes

The methane and isobutane chemical ionization mass spectra of alicyclic substituted 2-aryl-1,3-dithianes were examined by gas chromatography mass spectrometry. The protonated molecular ion was found to be of low abundance in the methane spectra, while a protonated cyclic sulfide cation (m/z 107) appeared as the base peak. A protonated molecular ion was the base peak when isobutane was used as the reagent gas. Electron impact mass spectra displayed weak molecular ions and were characterized by the m/z 106 fragment.     

Electron impact mass spectrometry of some 2-methyl-2-aryl- and 2-methyl-2-alkyl-1,3-dithianes

The electron impact mass spectrometric behaviour of four 2-methyl-2-aryl- and two 2-methyl-2-alkyl-1,3-dithianes is described and discussed in detail, with the aid of exact mass measurements, linked scans and mass-analysed ion kinetic energy spectrometry. The mechanism of the primary HS₂˙ loss, as well as those of the more unusual fragmentation pathways, are given.     

Electron impact studies. CXXIV—Negative ion mass spectra of organic functional groups. Thioacetanilides

The thioacetanilide negative molecular ion (produced by secondary electron capture) is stable, but it fragments after collisional activation to yield [C₆H₅NH]^? by cleavage α to the C?S grouping. The negative molecular ions of (substituted) o-nitrothioacetanilides undergo a series of extremely complex rearrangement reactions. For example, the molecular anion derived from o-nitro-N-methylthioacetanilide yields both acetate and thioacetate anions as major fragment ions.     

Electron impact mass spectra of 2-hydrazono-1,3-thiazolidin-4-one derivatives

Mass fragmentation of 2-hydrazono-1,3-thiazolidin-4-ones is dominated by two processes, namely cleavage of the hydrazone fragment with accompanying proton transfer from the latter to the thiazolidine ring, and cleavage of a hydrazone imide residue.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1117–1119, August, 1990.     

Electron impact mass spectra of meliacins

The electron impact mass spectra of some new meliacins and their derivatives are discussed. The major fragmentation modes include the functional group losses, the different ring cleavages and the loss of the furan residue as neutral fragments. A mechanism for the loss of the furan moiety from the molecular ion is discussed in detail with the help of deuterium labelling, high resolution and metastable data.     

Electron impact mass spectra of 5,5-bis(carboethoxy)-1,3-dioxanes

Electron impact-induced fragmentations of 2-substituted 5,5-bis(carboethoxy)-l,3-dioxanes were studied by exact mass measurements and metastable ion analysis. The substituent R on C(2) of the heterocyclic ring has little influence on the principal cleavage reactions. Elimination of CH₂O/CO and C₂H₄O/C₂H₄/C₂H₅OH are common fragmentations for ions containing the 1,3-dioxane moiety or the OC₂H₅ group, respectively. The abundant ions at m/z 173 and 127 serve as structural probes for the class of compounds studied. Primary fragmentations implying the ester function are of little importance.     

Electron impact mass spectrometry of nuphar alkaloids. II—Thiohemiaminals

The appearance of m/e 228 and 176 ions, useful in ascertaining the presence of the hemiaminal hydroxyl, are discussed for six thiaspirane-type hemiaminals isolated from Nuphar luteum and three epimeric pairs of α-thiohemiaminals derived from (–)-deoxynupharidine. Other groups of ions useful in ascertaining stereochemical differences of the sulfur moiety in α-thiohemiaminals are discussed for the same compounds. One such group of ions is comprised of 248, 246 and 231; a second is 192 and 191.     

Electron-impact studies—L: Skeletal-rearrangement fragments in the mass spectra of diphenylpyrazoles and -isoxazoles

The mass spectra of all diphenylpyrazoles and -isoxazoles contain rearrangement peaks at m/e 165 [C₁₃H₉]⁺. In addition, the spectra of 3,5-diphenylisoxazoles contain peaks at m/e 180 [C₁₃H₁₀N]⁺, which are produced by specific phenyl migrations. The mechanisms of both rearrangement processes have been studied by deuterium labelling.     

Electron impact mass spectra of some enamines

The mass spectra of α,β-diarylaminocrotonic acid anilides have been determined and the fragmentation pathways are now discussed. The proposed pathways have been confirmed by deuterium labelling, the spectrum of the model compound, or the appropriate metastables. The detailed electron impact data are given.     

Mass spectra of flavonoids. Electron impact mass spectra of flavan-4-ols

The electron impact mass spectra of seven flavan-4-ols are reported. Fragmentation pathways were investigated using deuterium labeling and high resolution measurements. The results are consistent with previously proposed ion structures for these compounds, but indicate that the mechanisms suggested for certain hydrogen rearrangements should be revised.     

Electron impact mass spectra of chlorinated methyl propanoates

The mass spectral fragmentations of all eleven chlorinated methyl propanoates have been studied. Deuterium labelling and metastable ion analysis were used to elucidate the fragmentation mechanism. The molecular ion peaks of all compounds are small, except methyl 3,3-dichloropanoate (38%). In most cases α-cleavage gives the base peak [COOCH₃]⁺, and the loss of a chlorine atom from the molecular ion is characteristic of the 3-chloro, 3,3-dichloro and 3,3,3-trichloro compounds. Metastable ions showed the losses of small neutral molecules such as CH₃OH, CH₂CO, CO₂ and CO from the [M? Cl]⁺ ion. α-Cleavage and the loss of Cl^˙ gives an intense [M? COOCH₃? Cl]^+˙ peak, which is the base peak in the spectra of the 2,3-dichloro and 2,3,3-trichloro compounds.     

Electron impact mass spectra of some new macropolycycles

Mass spectra of some macropolycycles have been studied. Normal and metastable (B/E) mass spectra are presented. The fragmentation patterns and the structures of the main ions are discussed.     

Electron impact mass spectra of synthetically modified milbemycins

The potent endectocide 23-(O-methyloximino)-F28249α and related compounds were identified and characterized by mass spectrometry. The fragmentation pathway of 23-(O-methyloximino)-F28249α was identified by its high-resolution mass spectrum and the electron impact unit mass spectra of its homologs. This fragmentation pathway is presented and discussed.     

Electron impact mass spectra of substituted β-nitrostyrenes

Peaks for the M^+., [M-OH]^+., [M-HNO₂]^+. and [M-H₂NO₂]⁺ ions are characteristic in the electron impact mass spectra of trans--nitrostyrenes. The loss of NO, CONO, and CHNO radicals is accompanied by isomerization of the molecular ions.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1926–1929, August, 1990.     

Electron impact studies. CV—negative ion mass spectra of functional groups. The trimethylsilyl group. Singly charghed and doubly charged ions

The 70 eV negative ion spectra of m- and p-nitrophenyltrimethylsilyl-ethers and -esters show pronounced molecular anions and simple fragmentation patterns. The spectra of the corresponding ortho isomers show peaks produced by rearrangement processes; these reactions have been studied by ²H and ¹⁸O labelling. p-Nitrobenzoyl derivatives of amino trimethylsilyl esters are of limited use for characterization of amino acids. Certain of the compounds studied produce a variety of dianions.