Electron-impact and thermal fragmentation patterns of some cyclic fluoroethers

The mass spectra of cyclic fluoroethers of the general formula (n = 1 to 4) are reported and discussed. Although these spectra show many similar features, those for which n = 3 and 4 contain intense peaks at m/e 63 which are only of relatively low intensity in the spectra of the other two. A similarity between the electron-impact and thermal fragmentation patterns of these compounds is noted.     

Pyrolysis of some perfluoroalkylene-linked aromatic imides

The pyrolysis of perfluoroalkylene-linked polyimides in an inert atmosphere has been studied using a pyrolysis-gas chromatographic-mass spectrometric method. The major primary gaseous degradation products were carbon monoxide and carbon dioxide. In addition large amounts of silicon tetrafluoride were produced by secondary reactions. Results obtained with 1,3-di-(3-phthalimidophenyl)hexafluo0ropropane and bis[N-phenyl-1,3-dioxo-isoindolyl(5,5′)]hexafluoropropane suggest that the perfluoroalkylene groups have a greater influence on the electron-impact induced fragmentation of the imide ring than on its thermal breakdown.     

Electron-impact fragmentation of aliphatic polynitro compounds

The mass spectra of two series of aliphatic polynitro compounds are reported and discussed. The fragmentation patterns of aliphatic nitro and polynitro compounds are similar in that no appreciable molecular ion current is observed; however, there are several other features in the fragmentation of aliphatic polynitro compounds which differ from that of nitroalkane spectra. Both series of compounds studied-C(NO₂)_x(CH₃)_4?x, where x = 4 to 0 and C₂(NO₂)_x(CH₃)_6?x, where x = 6,4,2-show a decrease in the number and intensity of alkylions with an increase in the NO⁺ and NO₂⁺ ion current as x increases. The main ions resulting from the more nitrated compounds are [NO]⁺, [NO₂]⁺, [CO₂]^+. and [CH₃CO]⁺, whose noncharged counterparts are the principal species produced in the detonation of these compounds. This similarity of the products of the two processes suggests the use of mass spectroscopy for the investigation of the initial explosive processes. The principal fragmentation pathways of the polynitroalkanes have been elucidated by exact mass measurements and the observation of metastable ion transitions.     

Electron-impact induced fragmentation of dimethanonaphthalene-type compounds

The mass spectra of endo,endo-1,2,3,4,4a,5,8,8a-octahydro-1,4:5,8-dimethanonaphthalen-anti-2-01 (Ia) and its endo,exo-2-ol (IIa) and endo,exo-10-ol (IIIa) isomers have been examined. Fragmentation schemes have been constructed on the basis of metastable transition measurements, accurate mass determination and deuterium substitution. A presence of the double bond in the molecule and a favourable hydrogen atom orientation in the vicinity of the double bond play an important role in the ion degradation process.     

Electron-impact promoted fragmentation of some substituted isoxazolidines

A series of substituted isoxazolidinylacetophenones (II to VI) have been shown to fragment subsequent to electron-impact in a generally predictable fashion. One characteristic fragmentation of all the compounds investigated was the loss of H₂O₂ from their respective molecular ions.     

Electron-impact induced fragmentation of some 5,10-di- hydrophenazastannines

The electron-impact induced fragmentation of four 5,10-dihydrophenazastannides [(I)-(IV)] was studied by low and high resolution mass spectrometry. Two of the compounds contain tin in the spiro position. To identify energetically favorable reaction paths, low electron-energy scans (12 eV) were taken along with 70 eV ones. The molecular ions fragment by consecutive ejection of the 10-substituents or, alternatively, by loss of R₂Sn. Subsequent fragmentation is accompanied by complex skeletal rearrangements and hydrogen migrations. An example of SnBr bond formation has been discovered. Ions of the phenanthridine type (m/e 179, C₁₃H₉N) are formed via enlargement of the center heterocyclic ring and rearomatization. Tentative mechanistic pathways are derived for all major fragmentation sequences on the basis of computer-aided correlation of metastable peaks, accurate mass measurements (elemental composition) and shifts resulting from specific deuterium labelling.     

A novel amination of aromatic and heteroaromatic compounds

Vinyl azides act as NH⁺₂ equivalents in reaction with aromatic or heteroaromatic lithium derivatives thus providing a direct method for amination of such compounds.     

Luminescence-laser classification of heteroaromatic and aromatic compounds.

The luminescent and laser properties of heteroaromatic and aromatic compounds are reviewed and discussed on the basis of all possible mutual arrangements of singlet and triplet states. All heteroaromatic compounds are divided into five classes. It is shown that a heteroaromatic compound can only be an effective laser dye if it belongs to class V (a situation where the Tnpi* level lies at higher energy than the S1(pipi*) level). Moreover, it is shown that the energy interval between the Tnpi* and S1(pipi*) states must be no less than 1000 cm - since the rate constant of the non-radiative process S1(pipi*)[symbol in text]Tnpi*[symbol in text]T1(pipi*) is usually 100 times greater than the fluorescence rate constant. The classification is extended to compounds with orbitals of pi/,pi*, pi,nupi* and pi/,nupi* nature. Pure aromatic compounds, the spectral-luminescent properties of which are solely determined by transitions of pi-electrons (pi --> pi*), are also divided into five classes, depending on the mutual arrangement of the Sp(1La), Salpha(1Lb), Tp(3La) and Tbeta(3Bb) states. It is found that only aromatic compounds of classes IV and V can be effective scintillators and laser dyes. It is also shown that the energy interval Salpha-Sp (for class IV) and Tbeta-Sp (for class V) must be no less than 1000 cm(-1). To illustrate the classifications for heteroaromatic and aromatic compounds, 12 specifically chosen compounds were studied experimentally and quantum chemically. The quantum yields, gamma and decay times, tauf of fluorescence in aerated and non-deaerated ethanol or cyclohexane solutions were measured. The oscillator strength, f(e), fluorescence rate constant, k(f), natural lifetimes, tauT(0) and intersystem crossing rate constants, kST are calculated. The laser ability of each of the compounds studied is tested. The suggested classification schemes can be extremely useful in the quest for effective scintillators and laser dyes among hypothetical heteroaromatic and aromatic molecules, enabling evaluation of these properties for a particular compound using only quantum chemical simulations.     

The sulfonation of aromatic and heteroaromatic polycyclic compounds

Relative reactivities of a series of polycyclic carbo- and heteroaromatic compounds to sulfonation by sulfur trioxide in nitrobenzene are measured and discussed. The results show the following reactivity in decreasing order: indole, carbazole, pyrene, perylene, naphthalene, phenanthrene, benzene, benzothiophene, and dibenzothiophene.     

Reactions of aromatic and heteroaromatic compounds having electron-acceptor substituents

The chloromethylation of 2-acetothienone and 2-formylthiophene with , -bischloromethyl ether in 60–100% sulfuric acid was studied. An increase in the acidity of the medium promotes the formation of 4-substituted products, which, as in nitration and bromination, is explained by protonation of the carbonyl group, leading to intensification of its electron-acceptor capacity.See [1] for communication VI.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1353–1357, October, 1971.     

Reactions of aromatic and heteroaromatic compounds having electron-acceptor substituents

The composition of the products formed in the bromination of complexes of furfural with AlCl₃ and methyl furan-2-carboxylate with AlBr₃ in chloroform and dichloroethane was studied by PMR spectroscopy and gas-liquid chromatography. Some literature data pertaining to these reactions are refined and corrected. The pathways for the formation of chloro derivatives under the examined conditions are discussed.     

Reactions of aromatic and heteroaromatic compounds containing electron-acceptor substituents

A method was developed for the preparation of 4-chloromethyl-2-acylthiophenes and m-(chloromethyl)acylbenzenes in up to 65% yields by the action of paraformaldehyde and anhydrous aluminum chloride on the corresponding carbonyl compounds. The reaction mechanism is discussed.See [1] for communication XXII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1474–1476, November, 1978.     

Reactions of aromatic and heteroaromatic compounds bearing electron-acceptor substituents

The specificity of the nitration and bromination of dimethyl(2-thienyl)sulfonium salts was studied. It was found that, in contrast to methyl 2-thienyl sulfide, which reacts to form 3- and 5-substituted derivatives, the sulfonium salts give a mixture of 4- and 5-substituted products. Total suppression of the activity of the position under the influence of the sulfonium grouping is not observed.See [1] for communication VIII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 310–314, March, 1972.     

Reactions of aromatic and heteroaromatic compounds bearing electron-acceptor substituents

Dimethyl(2-thienyl)sulfonium salts were synthesized for the first time. The corresponding triiodomercurates were obtained by the reaction of methyl 2-thienyl sulfide or its substituted derivatives with methyl iodide and mercuric iodide. Sulfonium perchlorates are formed as a result of the reaction of thiophene compounds with dimethyl sulfoxide in the presence of POCl₃ and perchloric acid. The HgI₃ ^– anion was replaced by NO₃ ^– by means of an anion-exchange resin. The methods for the dimethylation of sulfonium salts with conversion of them to the corresponding sulfides were studied; the conditions for obtaining quantitative yields from these reactions by means of an anion exchange resin in the acetate form were found.See [1] for communication VII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 165–168, February, 1972.     

Reactions of aromatic and heteroaromatic compounds bearing electron-acceptor substituents

Complexing with aluminum chloride can change the specificity of the bromination of furfural in such a way that the major product becomes 4-bromofurfural. Consequently, as in the thiophene series, reinforcement of the electron-acceptor capacity of the carbonyl group by means of the complexing deactivates the free 5 position so much that the 4 position of the furan ring becomes the most active.See [1] for communication X.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 597–600, May, 1972.     

Reactions of aromatic and heteroaromatic compounds containing electron-acceptor substituents

Synthetic methods based on accessible furan compounds of 5-benzyl(3-furyl)carbinol, a necessary component for the preparation of modified pyrethrins, were studied. The carbinol was obtained in 24% overall yield by a five-step synthesis starting from 4-bromofuran-2-carboxylic acid, for the preparation of which an improved method is proposed. Acylation of benzene with the chloride of the latter acid gave 4-bromo-2-benzoylfuran (in 77% yield), the reduction of which by the action of AlCl₃ + LiAlH₄ gave 4-bromo-2-benzylfuran (in 74% yield). The latter was treated with butyllithium and dimethylformamide to give 5-benzyl-3-formylfuran, which was converted to the carbinol in quantitative yield by the action of LiAlH₄.See [1] for communication XXI.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 306–310, March, 1978.     

Quantum-chemical investigation of some oligomeric heteroaromatic compounds

Indigo and its dimer, trimer, dehydro, and leuco forms were investigated within the framework of the Pariser-Parr-Pople method. The electronic structures of the compounds in the ground and excited states and the effect of chain lengthening are discussed, and the UV absorption spectra are interpreted. Several characteristics of the chromaticity of the investigated compounds as representatives of vat dyes are examined. The estimated (from calculations) energetic favorability of the indigoid, dehydro, and leuco forms of indigo is used in discussing the observed and experimental ease of redox transformations of indigo.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 794–798, June, 1972.     

Quantum-chemical investigation of some oligomeric heteroaromatic compounds

Those structures of aromatic imidazoles that can be realized in polybenzimidazoles were investigated within the framework of the computational scheme of the Pariser-Parr-Pople method. The features of the electronic structures of the investigated molecules were exposed. A judgment is expressed relative to the strength characteristics of the bonds in the imidazole rings during thermal or thermal oxidative destruction of aromatic polybenzimidazoles. The stereoisomerism of dibenzimidazoles was examined. The UV absorption spectra of the investigated compounds were interpreted.See [1] for communication III.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No, 10, pp. 1396–1402, October, 1973.     

Quantum-chemical investigation of some oligomeric heteroaromatic compounds

The characteristics of the electronic structures of a number of model aromatic oxazoles realized in aromatic polyoxazoles were obtained within the framework of the Pariser-Parr-Pople method. The UV spectra of most of them were interpreted. The stereoisomerism of dibenzoxazoles is examined.     

Quantum-chemical investigation of some oligomeric heteroaromatic compounds

The results of calculations by the Pariser-Parr-Pople method and the expanded Hückel method of oligomeric compounds and fragments from which aromatic polyimide macromolecules are constructed are presented and discussed. In connection with the controversial character of the problem of the structures of the intermediates in the destruction of polyimides and the use, in this case, of the concept of imide-isoimide rearrangement, the relative advantageousness of the tautomeric forms of imides is evaluated, the participation of the imide ring in one or another form in conjugation is discussed, the spectral differences in the forms are established, etc. The strength characteristics of the bonds in polyimides were estimated in connection with the possibility of homolytic and hydrolytic cleavage of polyimides at these bonds.See [1] for communication II.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No.8, pp. 1048–1056, August, 1972.