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.     

Electron impact studies. CXX—The properties of positive ions produced by charge stripping from negative ions. The acetate and perfluoroacetate cations

The ions [CF₃CO₂]⁺ and [CH₃CO₂]⁺ give peaks of small abundance in conventional positive ion spectra. These ions can be produced by collision-induced charge stripping of the corresponding stable negative ions. Six and ten fragment ions respectively are observed in the spectra of [CF₃CO₂]⁺ and [CH₃CO₂]⁺.     

Electron impact studies. CXIV—The occurance of metastable ions for two- and multi- stage decomposition of negative ions derived from p-nitrophenyl carboxylic acids

Pronounced metastable peaks are observed for the two-stage decomposition and the multi - stage elimination from p-NO₂C₆H₄(CH₂)_nCO₂H (n>1). ²H and ¹⁸O labelling shows that each process involves elimination of atoms from both the nitro and carboxyl groups. A consideration of the spectrum of p-nitrophenylcyclohexane-4-carboxylic acid leads to the proposition that interaction between the two functional groups is not a necessary prerequisite for the elimination of HO?.     

The negative ion mass spectra of mixtures of sulphur and organic compounds. I—The formation of [M+Sn]− from the mixture of sulphur and dinitriles

The negative ion mass spectra of sulphur, dinitriles and their mixtures were studied. The abundance of negative ions of sulphur was almost comparable to that of positive ions. In the negative ion mass spectrum of a mixture of sulphur and dinitrile, intense and characteristic peaks of [M + S_n]^? (n = 2, 3, 4, etc.) were observed resulting from ion–molecule association of dinitrile with the S_n^? anions. As a standard sample of a negative ion mass spectrum, sulphur itself has proved useful in the lower mass region (below m/e 256: S₈^?).     

Electron impact studies. CIII—Negative ion mass spectra of naturally occurring compounds: Nitrobenzoyl derivatives of amino esters

The negative ion mass spectra of p-nitrobenzoyl derivatives of amino esters show pronounced molecular anions and characteristic fragmentation patterns. Fragment anions observed in the spectra of o-nitrobenzoyl analogues arise by various interactions between the nitro and amino ester groups. No fragmentation of the amino ester residue is observed for the m-nitrobenzoyl derivatives, but the +E spectra of these systems can be used to provide definitive structural information.     

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.     

含磷杂环化合物的重排反应、互补离子及取代基效应

本文应用电子轰击质谱(EIMS)及亚稳离子的测定技术,研究了十四种新合成的含磷杂环化合物的碎裂机理,着重探讨了此系列化合物的重排反应、互补离子及取代基效应对离子丰度的影响。     

The negative ion mass spectra of mixtures of sulphur and organic compounds. II—the formation of [C5H5 + Sn]− from the mixture of sulphur and ferrocene

The negative ion mass spectra of ferrocene and of a mixture of ferrocene with sulphur were studied. In the spectrum of the mixture, characteristic peaks of [C₅H₅ + S_n]^? (n = 1, 2, 3 etc.) were observed. The structures of these ions are discussed.     

Ortho effects in organic molecules on electron impact. VI—Ortho effects of a carboxyl group in N-substituted anilines

The unusual fragments noticed in the mass spectra of N-benzyl- and N,N-dibenzylanthranilic acids have been explained on the basis of the ortho interaction of the carboxyl group with the N-benzyl- and N,N-dibenzyl moieties.     

Electron-impact studies. LXXXIV—Substituent effects in the negative ion mass spectra of aryl esters

Linear plots may be obtained for the fragmentations of aryl p-cyanobenzoates using the McLafferty approach, but the correlations are not as satisfactory as those observed¹ for aryl nitrobenzoates. Some satisfactory correlations of substituent effects are noted in the negative ion spectra of substituted benzyl-p-nitrobenzoates and substituted phenyl-(p-nitrophenyl)acetates. Pronounced rearrangement peaks are observed in the spectra of substituted phenyl-(p-nitrophenyl)acetates. Appearance potential studies suggest that the similarities in ρ values obtained¹ for the fragmentations of aryl m- and p-nitrobenzoate molecular anions are probably due to the correspondence between Hammett σ values and appearance potentials in the two series.     

Electron-impact studies. LXXXVII—ortho effects in the negative ion mass spectra of salicylates and anthranilates

The molecular anions of the methyl and phenyl esters of 4-nitrosalicylic acid and 5-nitroanthranilic acid eliminate ROH (R ? Me or Ph) by an ortho rearrangement. The molecular anions of phenyl 3-hydroxy-5-nitrobenzoate and phenyl 3-amino-5-nitrobenzoate lose PhOH to a lesser extent, and a study of the pressure dependence of these eliminations indicates the operation of simultaneous two-stage cleavage reactions. The competitive ortho effects observed when the nitro group is adjacent to either the ester or hydroxyl functions are described.     

Electron impact studies—LXVII. The mass spectra of alkyl-1,3-dithianes

The mass spectra of 1,3-dithiane, 2-methyl- and 2,2-dimethyl-1,3-dithiane have been studied by ²H labelling and metastable defocusing. The various molecular ions eliminate S₂H. to produce the ions [C₄H₇]⁺, [C₅H₉]⁺ and [C₆H₁₁]⁺ respectively, each of which scramble the hydrogens either before or accompanying further decomposition. Other processes are complex, but parallel those already reported for 2-aryl-1,3-dithianes.     

Ortho effects in organic molecules on electron impact: 19—Competing oxygen transfers from nitro group to sulphur and acetylinic carbons in 2-nitrophenylphenylethynylsulphides

Oxygen transfers to both the acetylenic carbons and sulphur are noticed in parallel fragmentation pathways during the electron-impact induced decompositions of 2-nitrophenylphenylethynylsulphides. Single oxygen transfer to acetylinic carbons leads to the most abundant ion corresponding to the benzoyl cation whilst double oxygen transfers to both the acetylenic carbons followed by the ejection of two CO units from the M⁺˙ ion afford another abundant fragment corresponding to the phenothiazine radical cation. However, the oxygen transfers to sulphur yield a less abundant [M ? SO₂H]⁺ ion. The proposed fragmentation pathways and the ion structures are sup ported by high-resolution data, collision-induced dissociation Linked-scan spectra and chemical substitution.     

Electron impact studies. CVII—Negative ion mass spectra of the oxime group. Monoximes derived from α-dicarbonyl systems

Specific losses of water are observed from the molecular anions of monoximes of α-diketones. Labelling studies, kinetic energy release values and the +E spectra of ions have been used to aid in the elucidation of the fragmentation pathways. It is proposed that the majority of ions have α-keto nitrile structures.     

Electron impact studies: CXXXI—Ion cyclotron resonance studies of ambident nucleophiles. The reaction between the thioacetate anion and thioacetic anhydride. A further example of a negative ion McLafferty rearrangement

The [MeCOS]^? ion undergoes reaction with neutral thioacetic anhydride in an ion cyclotron resonance cell to yield an adduct [M+MeCOS]^? which decomposes principally by loss of CH₂CS, thus establishing the occurrence of nucleophilic attack through O at the carbonyl centre.     

Electron impact mass spectra of some tertiary aliphatic nitro compounds. Nitrocarbonyl compounds and some analogues

The mass spectra of some tertiary aliphatic nitroaldehydes, nitroketones, nitroesters, nitronitriles and related nitrocarbonyl compounds are discussed and compared with those of some analogous nitro compounds lacking the carbonyl function. The M⁺˙ ? NO₂˙ and in several cases M⁺˙ ? HNO₂ fragmentation seem to be the most characteristic features of all tertiary aliphatic nitro compounds. In the presence of the primary nitro group, the loss of NHO₂ is always observed.     

Ortho effects in organic molecules on electron impact. V—ortho effects of the nitro group in n-substituted anilines

Some very interesting ortho effects are observed in the mass spectra of N-benzyl-o-nitroaniline and N,N-dibenzyl-2,4-dinitroaniline. Fragment ions arising from the transfer of oxygen from the nitro group to the benzylic carbon are seen in these spectra.     

Ortho effects in organic molecules on electron impact. IV—Ortho interaction of the carboxyl group with the olefinic bond in substituted benzoic acids

Fragments ions involving hydrogen migration from the –COOH group to the olefinic bond in the mass spectra of stilbene-2-carboxylic acid and ortho-carboxylbenzalaniline are discussed.     

Ortho effects in organic molecules on electron impact: 21—Oxygen transfers from the ortho nitro group to sulphur in N-aryl-2-nitrobenzenesulphenamides and phenyl-2-nitrophenyl disulphide

Fragment ions arising as a result of oxygen transfers from the nitro group to sulphur have been noticed in N-aryl-2-nitrobenzenesulpbenamides and phenyl-2-nitrophenyl disulphide. In the case of the former a double oxygen transfer to the sulphur has been noticed in the molecular ion whilst a single oxygen transfer to the β-sulphur atom and a double oxygen transfer to the α-sulphur atom have been observed in the latter. The proposed fragmentations are confirmed by high-resolution data, B/E linked-scan spectra and chemical substitution.     

Electron impact studies. CXII—The properties of positive ions produced by charge stripping from negative ions. [C6H5O]+, [C6H5S]+ and [C7H7S]+

The dissociative spectrum of the [C₆H₅S]⁺ ion derived by charge inversion from [C₆H₅S]^?, shows a variety of fragmentations including the competitive losses of H?, C₃H₄ and the formation of [CHS]⁺. The spectrum of a deuteriated derivative shows that these three processes are preceded or accompanied by H/D scrambling. The corresponding [C₆H₅O]⁺ species also undergoes hydrogen scrambling prior to fragmentation. In marked contrast, the ion [p-MeC₆H₄S]⁺ does not undergo hydrogen randomization between the methyl and aryl groups, and positional integrity is retained during fragmentation. These results are compared with the properties of the same ions produced by conventional ionization.