A study of rearrangement processes in the mass spectra of substituted diphenyl-ethers

An investigation of the mass spectra of a number of substituted diphenyl ethers has shown that the major fragment ions are commonly due to cleavage of the molecule into the two benzene ‘half’ fragments although in many cases the molecular ion is the most abundant species observed. Little evidence is seen of M? CO or M? CHO peaks in these molecules but a large number of different rearrangement processes have been observed which involve ortho-substituents. These rearrangement ions, although in some cases not very abundant, can be diagnostic in the problem of locating substituents in the diphenyl ether nucleus.     

Energy and substituent effects on the mass spectra of substituted benzophenones

For two competing decompositions of the same molecular ion to give products [A₁⁺] and [A₂⁺], the ratio [A₁⁺]/[A₂⁺], is equal to the ratio of rate constants for the formation of the stable ions. Thr ratios, [Y C₇H₄O⁺]/[C₇H₅O⁺], were determined for several benzophenones for electron energies from 15 to 70 eV. Plots of log [Y C₇H₄O⁺]/[C₇H₅O⁺] vs.[ω⁺] gave good straight lines at all energies. Similar correlations have been reported for log [Y C₇H₆⁺]/[C₇H₇⁺] from substituted diphenyl ethanes and are also true for substituted acetophenones, log [YøCO⁺]/[CH₃CO⁺]. A few charge exchange data were obtained which showed the same general trend as the electron-impact data and emphasize the contribution of low energy ions in the 70 eV mass spectra. Relatively poor correlations were obtained for the [Y C₆H₄⁺] and [C₆H₅⁺] ions that are formed by both one-step and two-step decompositions.     

A study of the ortho effects and rearrangement processes in the mass spectra of 2-arylaminothiazine and -thiazoline derivatives

The behaviour of the title compounds under electron impact has been investigated using low and high resolution mass spectrometry and partial ¹⁵N and D labelling. A number of ions produced by rearrangement were observed. Abundant ions are formed by intramolecular ortho substitution reactions (cyclizations), as demonstrated by energetic and kinetic considerations and by studying the decomposition pathways of these ions. The ortho substitution processes involve loss or rearrangement of an ortho group of the aromatic ring.     

Fragmentation and rearrangement processes in the high resolution mass spectra of diphenylsilyl compounds

High resolution mass spectra of a series of diphenylsilyl compounds, Ph₂SiX₂(X=H, F, Cl) and Ph₂Si(oy)₂ (Y=Et, Me, H), were recorded. Results from selected metastable defocusing experiments showed that if X or OY can be readily lost stepwise, the relative abundance of the biphenyl radical rearrangement ion (d) is small; if neutral silicon species such as :SiX₂, SiX or :Si(OY)₂ are readily eliminated, the relative abundance of the ion d will be large. The ion d originates from both odd- and even-electron ions, thus making the radical site mechanism, which requires a phenyl radical to polarize the other phenyl group, rather unlikely to be an important general driving force. The condensation of phenyl groups could be more appropriately viewed in terms of bond liability and product stability. In the special case of diphenylsilyl catecholate, in addition to geminal cleavage of phenyl groups, complex fragmentation and rearrangement processes were also observed.     

Skeletal rearrangement in the mass spectra of tetrasilaadamantanes

The loss of methyl group giving a peak of high intensity is observed in the mass spectra of 1,3,5,7-tetrasilaadamantanes. This skeletal rearrangement must involve the simultaneous rupture of three bonds and concomitant hydrogen transfer. The spectra of the tetrasilaadamantanes are considerably different from the spectrum of adamantane.     

Fragmentation and rearrangement processes in the mass spectra of perhalogeno-aromatic compounds—VII. Pentafluorophenyl derivatives of nitrogen

The mass spectra of several perfluoroaromatic nitrogen compounds, including primary and secondary amines, diamines, nitriles, hydrazines, azines and azo compounds, are presented. Fragmentation patterns of these compounds are described and the data are discussed in terms of comparisons amongst perfluoroaromatic nitrogen compounds, and with reference to the hydrogen substituted analogs, or to oxygen and sulfur analogs of a particular compound.     

A novel rearrangement reaction in doubly charged ion mass spectra of acetophenone derivatives

A novel rearrangement reaction for a methyl group is found in doubly charged ion mass spectra of p-substituted acetophenone derivatives. The driving force for the reaction is discussed.     

Rearrangement processes in the mass spectra of N-substituted sulphoximines

The electron-impact mass spectra of a range of N-substituted sulphoximines have been recorded and rationalised. Intense peaks consistent with oxygen-to-sulphur and sulphur-to-sulphur migrations were observed in the spectra of some of the compounds.     

Thermal isomerization of the isoxazole ring and rearrangement processes in the mass spectra of 3-aryl-5-methylisoxazole-4-carboxylic acids

The mass spectra of 15 compounds of 3-aryl-5-methylisoxazole-4-carboxylic acid and their derivatives were investigated. Thermal isomerization of the isoxazole ring was observed for several derivatives of this series. The formation of rearranged pseudomolecular ions of the arylamines during the dissociative ionization of 3-aryl-5-methylisoxazole-4-carboxylic acids was examined on the basis of a study of the mass spectra of labeled compounds. It is assumed that there is a high probability of concerted elimination of several groups in the first step of the disintegration of the molecular ion.     

Fragmentation and rearrangement processes in the mass spectra of perhalogenoaromatic compounds. XII-pentafluorophenyl derivatives af phosphorus (V) halides

The Mass spectral fragmentation processes for a number of alkyl and aryl subtituted phosphinyl and phosphonyllk halides and their thio analogs are discussed with respect to two intramolecular rearrangment processes. The first is aryl fluorine transfer to phosphorus and the second concerns a rearrangement depicted as follows, i.e. a reverse Arbuzov reaction RR′XP?S→RXP? S? R′. Both pathways are supported by evidence obtained form metastable ions and mass analyzed ion kinentic energay spectra. The previously observed phenomenon of subtituent coupling is also describedc where ita occurs in the phosphinyl compounds. The mass spectra of a number of mixed fluoro-pebtafkuorophenyl phosphorances are also discussed.     

Substituent effects on the mass spectra of substituted phenyl acetates

The mass spectra of a series of meta- and para-substituted phenyl acetates have been examined. Substituent effects have been correlated with Δ (AP-IP) values and by using the Harrison and Chin approach. The bond-cleavage and rearrangement reactions of phenyl accetates are compared with the corresponding reactions of acetanilides and the differences attributed to the degree of transmission of polar effects in the two systems.     

Fragmentation and rearrangement processes in the mass spectra of perhalogenoaromatic compounds—VIII: Fluoroaromatic heterocyclic derivatives of group IV

The metastable ion supported fragmentations and fluorine transfer rearrangements of a series of fluoroaromatic heterocyclic derivatives of silicon, germanium and tin are reported. Of particular interest is the unique loss of neutral SiF₄ from the parent ion of (C₁₂F₈)Si yielding the [C₂₄F₁₂]⁺˙ ion. These and similar rearrangements are discussed and structures are proposed for some of the ions observed. The general case of cyclic rearrangement intermediates prior to the loss of neutral metal fluorides from perfluoroaromatic derivatives is discussed. Losses of neutral metal fluorides from the parent ions appear to involve a species with increased co-ordination number about the central atom as an intermediate. In addition to (C₁₂F₈)₂M, the following compound types were studied: (C₆H₅)₂Ge(C₁₂F₈), (C₁₂F₈S)₂M and R₄Sn₂(C₆F₄)₂ (where M = a Group IV metal and R = CH₃ or C₆H₅).     

A mass spectrometric study of substituted furfuryl compounds

The mass spectra of six furfuryl compounds — namely, furfuryl alcohol, 5-furfuryl-furfuryl alcohol, difurfuryl ether, difurylmethane, 2,5-difurfurylfuran, and 4-furfuryl-2-pentenoic acid-γ-lactone — have been studied. Their fragmentation mechanisms are discussed in detail with particular emphasis on the modes that lead to the formation of aromatic fragments. The majority of the fragment ions are formed by elimination of CO and C₂H₂ from even-electron precursor ions and HCO from odd-electron precursor ions. Molecules containing two furan rings linked by a methylene group give mass spectra that exhibit large abundances of aromatic fragment ions.     

Cyclic ions in the mass spectra of trimethylsilyl derivatives of substituted o-dihydroxybenzenes

The mass spectra of trimethylsilyl (TMS) ethers/methyl esters of phenolic acids containing o-dihydroxybenzene groups have base peaks at [M?119]⁺ instead of the usual [M?15]⁺ and [M?31]⁺ that are characteristic of TMS/methyl esters of monohydroxyphenolic acids. These ions, formed by the loss of 31+88 u from the parent ion, possess a cyclic moiety as proven by substitution of deuterium atoms for hydrogen atoms in the TMS groups of the methyl esters of 3,4,5-trihydroxybenzoic (gallic), 3,4-dihydroxybenzoic (protocatechuic) and β-(3,4-dihydroxyphenyl)propenoic (caffeic) acids. Although these cyclic ions are the base peaks in TMS-derivatized o-dihydroxyphenolic acid esters, similar ions represent intense peaks but not necessarily the base peak in other derivatized compounds such as 1,2-dihydroxybenzene, 1,2-dihydroxy-3-methyl- and 1,2-dihydroxy-4-methyl-benzenes and flavan-3-ols that possess o-dihydroxybenzene groups. Compounds possession m- or p-dihydroxybenzene groups do not form these cyclic ions; therefore, this procedure for derivatization and interpretation of mass spectra is valuable for the identification of compounds containing o-dihydroxybenzene groups in complex mixtures of isomeric compounds.     

Electron-impact studies—LXXIV: A survey of rearrangement processes in the ‘doubly-charged ion’ mass spectra of aromatic compounds

The technique of Beynon² has been used to determine the ‘doubly-charged ion’ mass spectra of a variety of aromatic compounds which contain pronounced rearrangement peaks in their conventional mass spectra. Many, but not all, of the ‘doubly-charged ion’ spectra contain similar rearrangement peaks to those observed in conventional spectra.     

Beckmann rearrangement in benzophenone oxime,a mass spectrometric study

The isomerization of benzophenone oxime to benzanilide, previously observed to take place in the ion source of a mass spectrometer and attributed to a Beckmann type rearrangement of the benzophenone oxime molecule ion, has been shown to occur by a thermal mechanism prior to ionization. Mass spectrometric evidence is supplemented by infrared spectrophotometric examination of solid samples and shows that in the solid state, at room temperature, benzophenone oxime has a lifetime of about 600 h.     

Ultraviolet absorption spectra of substituted phenols: a computational study

Vertical excitation energies for electronic transitions from the ground state to the first two excited states of phenol, mono- and disubstituted methoxyphenols and methyl-substituted phenols have been characterized with the Time-Dependent Density Functional Theory (TD-DFT), the Complete Active Space Self-Consistent Field method (CASSCF) and the Coupled Cluster with Single and Double Excitations Equation-of-Motion approach (CCSD-EOM) to simulate and interpret experimental ultraviolet absorption spectra. While CASSCF excitation energies for the first two transitions either are grossly overestimated or exhibit a weak correlation with experimental data, both TD-DFT and CCSD-EOM perform very well, reproducing the spectral shifts of both the primary band and secondary band observed upon substitution. The conformational dependence of the calculated excitation energies is generally smaller than the shifts caused by substitution.     

Rearrangement processes in the mass spectra of some 3,5-dimethylisoxazole derivatives

The mass spectra of isoxazole and some 3,5-dimethylisoxazole derivatives were investigated. Schemes for the formation of the principal rearranged ions are proposed on the basis of a study of the dissociative ionization of labeled compounds. Examples of the effect of electronic and steric factors on the probability of the existence of different channels for disintegration of the molecular ion are presented. It is shown that the formation of an ion with mass 82 during the dissociative ionization of a number of the investigated compounds occurs via different mechanisms as a function of the nature of the substituents in the 4 position of the isoxazole ring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1336–1340, October, 1972.     

Fragmentation selectivity in electron impact ionization mass spectra of substituted dimethoxybenzenes

Several 1-X-sabstitirted-3-methoxy-4-trideuteromethoxybenzens were synthesized and their electron impact ionization mass spectra were measured with an ionizing energy of 20 eV. From the peak intensity ratio of [M ? CD₃ ] and [M ? CH₃] the fragmentation-directing ability of the substituent X was evaluated. The most powerful group was found to be NH₂, which expelled a methoxy methyl group only from its para position. The CH₃ group and four halogen atoms, F, Cl, Br and I, exerted a moderate effect Electron-withdrawing groups such as NO₂, CHO and CN had only a little influence on the fragmentation selectivity. These results were interpreted in terms of the effect of X on the distribution of both the unpaired electron and the positive charge in the molecular ion.