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.     

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 part 22. Competing oxygen transfers from the nitro group to sulphur and the olefinic double bond in 2-nitrophenyl styryl sulphides

Double oxygen migration to sulphur from the ortho-nitro group leading to eliminations of SO₂ and ^·SO₂H from the molecular ions and single oxygen transfer to the olefinic double bond in the side-chain giving rise to the most abundant ion at m/z 138 have been observed in 2-nitrophenyl styryl sulphides on electron impact. The proposed fragmentation mechanisms and the product ion structures were confirmed with the aid of high-resolution data, B/E linked scan and CID spectra.     

Ortho effects in organic molecules on electron impact. Part 15. Oxygen transfers from the nitro group to both sulphur and olefinic double bonds in allyl o-nitrophenyl sulphide

An oxygen transfer from the nitro group to the C?C group, followed by a simple cleavage, afford intense fragments corresponding to o-nitrosothiophenol at m/z 139 and o-nitrosothiophenoxy cation at m/z 138 during mass spectral fragmentations of allyl o-nitrophenyl sulphide. Further, a concerted double oxygen transfer from the nitro group to the sulphur is proposed for the ejection of ?O₂H from the molecular ion of this compound, leading to the quinolinium cation at m/z 130. These processes are supported by the high-resolution data, collision-induced dissociation linked-scan spectra and chemical evidence.     

Ortho effects in organic molecules on electron impact. 14—Concerted and stepwise ejections of SO2 and N2 from N-arylidene 2-nitrobenzenesulphenamides

Unexpected ortho interaction of the nitro group has been noticed during the mass spectral fragmentations of N-arylidene 2-nitrobenzenesulphenamides, where the molecular ions expel SO₂ and N₂ both in concerted and stepwise processes. Loss of a hydrogen or the substituent from this fragment leads to a very abundant ion in all the compounds studied. Based on chemical evidence and linked-scan studies, a 1,2-phenylenetropylium cation structure has been postulated for the [M–SO₂–N₂–H/substituent]⁺ ion.     

Ortho effects in organic molecules on electron impact. Part 16. Novel oxygen transfers from the nitro group to acetylenic carbons in 2-nitrodiphenylacetylenes

Oxygen transfers to both acetylene carbons are noticed in parallel fragmentation pathways during the electron impact induced decompositions of 2-nitrodiphenylacetylene. The oxygen transfer to β-acetylenic carbon leads to the most abundant ion corresponding to benzoyl cation while transfer to the α-acetylenic carbon affords less intense fragments corresponding to [M? OH]⁺, [M? CO]^{+ ˙} and [M? CO₂]^{+ ˙}. The proposed fragmentation pathways and ion structures are supported by high-resolution data, linked-scan spectra and chemical substitution.     

Ortho,Effects in organic molecules on electron impact: X—unusual ortho effects of the methyl group in o-picolinotoluidide

The mass spectrum of o-picolinotoluidide gives rise to three major fragments at m/z 184, m/z 169 and m/z 168, corresponding to the loss of CO from the molecular ion followed by the loss of ?H₂ and ?H₃ by independent pathways. It has been shown that the ortho methyl group and the nitrogen of the pyridine ring in the 2-position are involved in the formation of these three major fragments observed in the mass spectrum of o-picolinotoluidide. The mass spectrum of 2-(o-toluidino) pyridine, the molecular ion of which can resemble the [M? CO]⁺ ion in o-picolinotoluidide, also shows loss of CH₃ and NH₂ radicals from the molecular ions. Based on these observations coupled with the high resolution data, the mass analysed ion kinetic energy spectrometry and high voltage scans of these fragments in both the compounds, two mechanistic pathways have been proposed for the formation of these ions in o-picolinotoluidide.     

Ortho effects in organic molecules on electron impact: XI—the interesting ortho effect of the methoxy group in o-methoxy aromatic thioamides

It has been noticed that the major part of the loss of ?H from the molecular ion of most of the o-methoxythioamides results from an ortho effect of the methoxy group. Comparison of the MIKE spectra of the [M? SH]⁺ of 1-(2-methoxyphenylthioxomethyl)piperidine and 1-(2-methoxyphenylthioxomethyl)pyrrolidine with the MIKE spectra of [M? SH]⁺ of the corresponding unsubstituted compounds, reported earlier, indicated two parallel pathways for the formation of [M? SH]⁺ in the o-methoxy compounds. In the first pathway, as has been noticed in thioamides in general, the loss of ?H involves the migration of either the α-hydrogen in the amine moiety or the hydrogen attached to nitrogen. In the second pathway, the migration of a hydrogen from the o-methoxy group to the sulphur atom followed by ejection of SH from the molecular ion leads to a stable cyclized ion. Interesting secondary fragmentations as a consequence of this ortho effect have also been noticed.     

Ortho effects in organic molecules on electron-impact I—Oxidation of olefinic double bond by the ortho nitro group in stilbazoles

The electron-impact-induced fragmentation in 2′-nitro-4-stilbazole is triggered by the oxidation of the olefinic double bond by the ortho nitro group in the initial step, while such an interaction under the same condition is totally absent in the meta and para isomers. The important fragmentation in 2′-nitro-2-stilbazole is the formation of a cyclised ion with the elimination of the nitro group.     

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.     

Ortho effects in organic molecules on electron impact: 18—Novel hydrogen transfer from the methoxy group to acetylenic carbon in 2-methoxyphenylacetylene and 2-methoxydiphenylacetylenes

The transfer of a hydrogen from the ortho methoxy group to the acetylenic carbon in 2-methoxyphenylacetylene under electron impact conditions affords the rearranged molecular ion corresponding to 2H-1-benzopyran. Similar processes leading to cyclic products are also noticed in 2-methoxydiphenylacetylenes. The ion structures and the mechanism of fragmentations are established through high-resolution data, collision-induced decomposition, mass-analysed ion kinetic energy spectra, B/E linked scan spectra, D-labelling and chemical substitution.     

Ortho effects in organic molecules on electron impact 13—mechanism of decarboxylation in o-carboxy heteroaromatics

Expulsion of CO₂ from the molecular ions of the 2-(2-carboxyphenyl) derivatives of benzoxazole, benzothiazole and benzimidazole gives rise to the base peaks on electron impact. The proposed mechanism for this fragmentation process, involving the anchimeric assistance of the heteroatom by the initial abstraction of the H˙ from the carboxyl group followed by the expulsion of CO₂ from the molecular ions, is supported by the study of the linked scan 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 of a nitro group in 2′,3′ and 4′monosubstituted-trans-2,4-dinitrostilbenes on electron impact. IV

The mass spectral fragmentation patterns of thirteen 2′,3′ and 4′-R-trans-2,4-dinitrostilbenes obtained by electron impact have been studied. The main routes of fragmentation involves loss from the molecular ion due to the ortho effects of the 2-nitro substituents. Substitution on positions 2′,3′ and 4′ of stilbene moiety does not influence the fragmentation patterns.     

Ortho effects in organic molecules on electron impact. 12—Mechanism of the H2O loss from the molecular ion of 2-(phenylamino)benzoic acid

The mass spectrum of 2-(phenylamino)benzoic acid is characterized by the presence of the base peak at m/z 195, formed by the expulsion of H₂O from the molecular ion. A mechanism for the water loss, involving the ? COOH and ? NH functions followed by cyclization leading to the molecular ion of acridone, is proposed based on the study of the substituted derivatives and MIKE spectra.     

Electron impact induced hydrogen migrations in organic molecules: IV—novel hydrogen transfers in alkyl o-methoxybenzoates

Simultaneous hydrogen transfers—one from the methoxy group and the other from the alkyl group—to both the oxygen atoms of the ester function result in the formation of a common ion at m/z 152 in the alkyl o-methoxybenzoates on electron impact. Expulsion of the formyl radical from this ion leads to a fragment resembling the protonated benzoic acid. Another novel feature in these compounds is the loss of H₂O from the [M? R]⁺ ion which arises through an ortho effect during a secondary fragmentation process.     

Electron impact studies CX—+E spectra from negative ions. Ortho effects and skeletal rearrangement reactions from sulphur compounds

+E spectra derived from the non-decomposing anion of some sulphur compounds are independent of the pressure of the collision gas. The compounds chosen for study contain peaks produced from either ortho effects or skeletal rearrangement fragments in their conventional positive ion spectra. The dissociative +E spectra are either devoid of skeletal rearangement ions or alternatiely contain such peaks in small abundance. In contrast, peaks derived from ortho reactions are present in high abundance.     

Ortho effects in organic molecules on electron-impact II– Ortho effects in substituted α,α,α-trichloracetanilides

Elimination of trichloromethyl radical from the molecular ion is the abundant fragment in the mass spectra of most of the thirteen substituted trichloracetanilides studied. Unusual ortho effects of ? OCH₃, ? NO₂ and ? COOH groups are noticed only after the initial ejection of trichloromethyl radical from the molecular ion.     

Novel proximity effects and Ortho interactions in 2,2′-disubstituted diphenylamines on electron impact

Unexpected ejections of CH₃NO₂/[^˙CH₃ + ^˙NO₂], N₂O₄/[^˙NO₂ + ^˙NO₂] and CH₃OCH₃/[^˙CH₃ + ^˙OCH₃] were observed from the molecular ions of 2-methoxy-2′-nitrodiphenylamine, 2,2′-dinitrodiphenylamine and 2,2′-dimethoxydiphenylamine, respectively, under electron impact conditions owing to proximity effects. In other competing fragmentation pathways, novel proximity effects triggered by the ortho interactions leading to the unusual eliminations of [^˙CH₃ + H₂O] from M^+˙ of 2-methoxy-2′-nitrodiphenylamine and HNO₃/[^˙NO₂ + ^˙OH] from M^+˙ of 2,2′-dinitrodiphenylamine were observed. Evidence for the interpretation of the main fragmentation pathways was obtained from the metastable ion spectra and high-resolution mass spectrometry. Confirmation of the structures assigned to the ions was provided by collision-activated dissociation mass-analysed ion kinetic energy spectra.     

Mass spectrometry of condensed N-heterocycles: II—A novel ortho effect in the electron impact induced fragmentation of some C-(2-nitrophenyl)-azoles and -azoloazines

Heterocycles containing an integrated 2-nitrobenzaldehyde imine moiety produce ions of m/z 134 with high abundance under electron impact. As shown by kinetic energy release measurements these ions have the same structure in all the cases studied, identical to m/z 134 formed from the reference compound 2-nitrobenzoylpiperidide. The mechanism of formation of m/z 134 most probably involves isomerization of its precursor ion to give a spiro intermediate, from which m/z 134 arises either synchronously or after a second isomerization. Both alternatives formally represent an oxygen transfer from the nitro group to the imino carbon via a 5-membered transition state.