The mass spectral fragmentation of phenyl ω-dialkoxyethyl tellurides

The 70 eV mass spectrum of phenyl ω-dimethoxyethyl telluride [C₆H₅? Te? CH₂CH(OR)₂, R?CH₃]contains an intense peak at m/z 238 which corresponds to a rearrangement ion [C₆H₅? Te? OR]⁺. The formation of this species is further illustrated by the presence of a peak at m/z 241 in the spectrum of the hexadeuterated analog (R?CD₃) and a peak at m/z 252 in the spectrum of the ethyl analog (R?CH₂CH₃). These combined results illustrate the presence of only one of the alkoxyl groups in the rearrangement ion. Several other abundant ions that contain oxygen but not tellurium are present in the spectra of these compounds. High resolution analyses have aided in the determination of the origin and composition of several of the characteristic ions formed upon electron impact fragmentation of phenyl ω-dimethoxyethyl telluride.     

The mass spectra of some phenyl pyridyl ketones

The mass spectra of phenyl 2-pyridyl, phenyl 3-methoxy-2-pyridyl, phenyl 4-methoxy-2-pyridyl, phenyl 5-methoxy-2-pyridyl, phenyl 6-methoxy-2-pyridyl ketones, phenyl 3-pyridyl and phenyl 6-methoxy-3-pyridyl ketones, and phenyl 4-pyridyl ketone were studied. The major fragmentation pathway of all the ketones results in the formation of[C₆H₅CO]⁺ and [C₅H₄NCO]⁺ type ions. Another fragmentation path is the loss of carbon monoxide with formation of an [M ? CO]⁺ ion after skeletal rearrangement.     

The mass spectra of some alkyl and aryl imidazolines

The mass spectra of mono- and di-substituted alkyl and aryl imidazolines have been measured and the spectra analysed with the aid of deuterium labelling and high resolution techiques. In contrast to the fragmentation of thiazolines, all principal fragments of the imidazoline ring contain one nitrogen with or without hydrogen migration. In the case of 2,4-disubstituted imidazolines, the presence of two tautomeric molecular ions are suggested.     

The mass spectra of some alkyl and aryl oxazoles

The mass spectra of a variety of alkyl and aryl oxazoles have been determined and the spectra analyzed with the aid of deuterium labelling and high resolution mass spectrometry. In contrast to the corresponding benzenoid compounds, the mass spectra of isomeric alkyl oxazoles are distinctive and in this respect are akin to those of the corresponding pyridines. Further analogy to the pyridines is suggested by the unfavorable nature of a carbonium ion adjacent to the 2-position and this effect may be used to locate alkyl substituents attached to the oxazole nucleus. The loss of carbon monoxide from the molecular ions of 2,5-disubstituted oxazoles probably occurs with ring opening and migration of the C-5 substituent (e.g.Br) to the C-4 position.     

二烷氧基膦酰乙酸酯的电子轰击正离子和化学电离负离子质谱研究

本文报道一系列二烷氧基膦酰乙酸酯的电子轰击(EI)正离子和甲烷化学电离负离子(NCI)质谱.在EI谱上出现特征的[M+H]^+离子,进一步发生氢重排,然后失去烯烃,再失水和脱CH2CO.而在NCI谱中则生成[M-H]^-离子(基峰),易失去烷基,再失烷氧基和CH2CO,或氢重排后脱烯烃.正、负离子的断裂机理不同,但数据可以互相补充,以利于类似未知物的结构分析.     

Photoelectron spectra of vinyl tellurides

The lowest energy band in the photoelectron (PE) spectra of alkyl vinyl tellurides is attributed to-MO with predominant contribution from the p_z-AO of the tellurium atom. The second and fourth lowest energy bands correspond to-MO. An additional-MO is located between these-MO. The introduction of a second vinyl group hardly affects the HOMO. The heterocyclization of divinyl telluride has a large perturbation effect. Nevertheless, divinyl telluride and tellurophene have the same type of orbital structure.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 935–939, April, 1991.     

Interpretation of alkyl diselenide and selenosulfenate mass spectra

The mass spectral fragmentation of aliphatic diselenides and selenosulfenates is analyzed to gain a better understanding of the behavior of these species. The main fragmentation pathways of these species include the fragmentation along the Se-C bond, fragmentation along the Se-Se or Se-S bonds and intra-molecular rearrangements. In general, negative ionization favors the fragmentation along the Se-Se or Se-S bonds while positive ionization leads to stable molecular ions. Density functional theory calculations of bond dissociation energies and molecular orbital analysis was undertaken to explain the observed trends in molecular fragmentation. Besides the analysis of molecular fragmentation, a phenomenon of molecular association in negative electron impact and positive chemical ionization conditions was observed and investigated using a high resolution time-of-flight mass spectrometer. Molecular association that occurs during the ionization of species includes the formation of symmetrical diselenides from asymmetrical selenosulfenates and formation of alkylseleno adducts from the corresponding diselenides. For species which is hard to resolve by mass analysis, such as isobars of CHSe, CH₂Se, and CH₃Se, the isotope pattern superimposition procedure was applied to define the overlapping clusters.     

Cyclization reactions in the chemical ionization spectra of bifunctional alkyl phenyl ethers

Evidence is presented for the formation of cyclic onium ions from bifunctional alkyl phenyl ethers under chemical ionization conditions.     

On the mass spectra of some alkyl digermanium compounds

This paper reports the monoisotopic mass spectra of the compounds (CH₃)Ge? Ge(CH₃)₃,(C₂H₅)₃Ge? Ge(C₂H₅)₃ and (CH₃)₃Ge? Ge(C₂H₅)₃. With the aid of metastable ion transitons and appearance potentials the fragmentation patterns can be given. The dominant reactions are explained in terms of the valence of the metal atom. According to the valence rule the possibility of forming an ion in which two germanium atoms are bonded to five other groups (alkyl or hydrogen) determines greatly the spectra, while successive elimination of the methyl groups appears to be difficult and elimination of the ethyl groups is a predominant process.     

The fragmentation of ionized alkyl phenyl ethers

The energetics of olefin loss from ionized alkyl phenyl ethers have been determined by ionization and appearance energy measurements. It is concluded that the reaction is governed by one or more of three features: (i) the strength of the bond between the phenoxy radical and the alkyl ion; (ii) the ease of isomerization of the alkyl ions, chiefly by H-shifts therein, and (iii) the strength of the C? H bond (primary, secondary and tertiary) involved in the H transfer to oxygen which precedes the olefin loss. The possible participation in the reaction of distonic ions and proton bound radical-molecule pairs is also discussed.     

The mass spectra of the trimethylsilyl derivatives of some alkyl and aminoalkyl phosphonates

The mass spectra of the trimethylsilyl derivatives of a series of alkyl and aminoalkyl phosphonates were investigated with the aid of deuterium labeling and high resolution mass measurements. The spectra contained several prominent ions characteristic of the phosphonate system and a number of ions produced by inter and intra molecular migration and interaction of trimethylsilyl groups.     

Substituent effects in the mass spectra of diethyl phenyl phosphates

The mass spectra of diethyl phenyl phosphates show substituent effects with electron-donating groups favouring the molecular ion M⁺˙, and the [M? C₂H₄]⁺˙, [M – 2C₂H₄]⁺˙ and [XPhOH]⁺˙ ions. The [PO₃C₂H₆]⁺ (m/z 109) and [PO₃H₂]⁺ (m/z 81) ions are favoured by electron-withdrawing groups. Results suggest that the formation of the [XPhC₂H₃]⁺˙ ion involves rearrangement of C₂H₃ to the position ortho to the phosphate group. Ortho effects are also observed.     

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.     

Electron impact mass spectra of some enols and their alkyl ethers

The mass spectra of α-arylamino-β-hydroxycrotonic acid anilides and their O-methyl and O-ethyl ethers have been determined and the characteristic fragmentation pathways are discussed. The proposed fragmentation patterns are supported by the appropriate metastables and deuterium labelling.     

Photosensitized oxidation of alkyl phenyl sulfoxides. C-S bond cleavage in alkyl phenyl sulfoxide radical cations

The 3-cyano-N-methylquinolinium perchlorate (3-CN-NMQ(+)ClO4(-))-photosensitized oxidation of phenyl alkyl sulfoxides (PhSOCR1R2R3, 1, R1 = R2 = H, R3 = Ph; 2, R1 = H, R2 = Me, R3 = Ph; 3, R1 = R2 = Ph, R3 = H; 4, R1 = R2 = Me, R3 = Ph; 5, R1 = R2 = R3 = Me) has been investigated by steady-state irradiation and nanosecond laser flash photolysis (LFP) under nitrogen in MeCN. Steady-state photolysis showed the formation of products deriving from the heterolytic C-S bond cleavage in the sulfoxide radical cations (alcohols, R1R2R3COH, and acetamides, R1R2R3CNHCOCH3) accompanied by sulfur-containing products (phenyl benzenethiosulfinate, diphenyl disulfide, and phenyl benzenethiosulfonate). By laser irradiation, the formation of 3-CN-NMQ(*) (lambda(max) = 390 nm) and sulfoxide radical cations 1(*+) , 2(*+), and 5(*+) (lambda(max) = 550 nm) was observed within the laser pulse. The radical cations decayed by first-order kinetics with a process attributable to the heterolytic C-S bond cleavage leading to the sulfinyl radical and an alkyl carbocation. The radical cations 3(*+) and 4(*+) fragment too rapidly, decaying within the laser pulse. The absorption band of the cation Ph2CH(+) (lambda(max) = 440 nm) was observed with 3 while the absorption bands of 3-CN-NMQ(*) and PhSO(*) (lambda(max) = 460 nm) were observed just after the laser pulse in the LFP experiment with 4. No competitive beta-C-H bond cleavage has been observed in the radical cations from 1-3. The C-S bond cleavage rates were measured for 1(*+), 2(*+), and 5(*+). For 3(*+) and 4(*+), only a lower limit (ca. >3 x 10(7) s(-1)) could be given. Quantum yields (Phi) and fragmentation first-order rate constants (k) appear to depend on the structure of the alkyl group and on the bond dissociation free energy (BDFE) of the C-S bond of the radical cations determined by a thermochemical cycle using the C-S BDEs for the neutral sulfoxides 1-5 obtained by DFT calculations. Namely, Phi and k increase as the C-S BDFE becomes more negative, that is in the order 1 < 5 < 2 < 3, 4, which is also the stability order of the alkyl carbocations formed in the cleavage. An estimate of the difference in the C-S bond cleavage rate between sulfoxide and sulfide radical cations was possible by comparing the fragmentation rate of 5(*+) (1.4 x 10(6) s(-1)) with the upper limit (10(4) s(-1)) given for tert-butyl phenyl sulfide radical cation (Baciocchi, E.; Del Giacco, T.; Gerini, M. F.; Lanzalunga, O. Org. Lett. 2006, 8, 641-644). It turns out that sulfoxide radical cations undergo C-S bond breaking at a rate at least 2 orders of magnitude faster than that of corresponding sulfide radical cations.     

Aryl versus alkyl and vinyl migration in the mass spectra of sulphone derivatives

The 2-acetoxyethyl aryl sulphones were found to be unsuitable for a comparative study with the corresponding chlorides and alcohols as their predominant fragmentation involved cleavage of the aliphatic carbon-sulphur bond with charge retention on the aliphatic part of the molecule The expected McLafferty rearrangement to yield an intermediate vinyl species was only a minor fragmentation path. Indirect evidence for alkyl migration in the molecular ion was found in the spectrum of 2-acetoxyethyl 1-paranitro phenyl sulphone. The spectra of the aryl vinyl sulphones revealed intense [Aryl SO]+ ions resulting from preferred migration of the vinyl group from sulphur to oxygen.     

The mass spectra of cyclopropabenzenes

Cyclopropabenzene, 1,1-difluorocyclopropabenzene and their 2,5-diphenyl analogues were studied by mass spectrometry. With the help of deuterium labelling, complete hydrogen scrambling was shown to occur before the loss of a hydrogen atom from the molecular ions.