Mass spectral fragmentation of some phosphaaromatic compounds

The behaviour of 2-phosphanaphthalene, 3-methyl-phosphanaphthalene and 10-methyl-9-phosphaanthracene upon electron-impact has been compared with that of the carbon and nitrogen analogues. A close resemblance to the fragmentation pattern of the [M ? H]+ ions of 2-methyl-and 2-ethylbenzo[b]thiophene has been observed. It is concluded from the σ₄₀ intensities of the molecular ions, the relatively high intensities of the doubly charged molecular ions and the fragmentation patterns, that these phosphorin derivatives behave as aromatic compounds under electron-impact. From the molecular ion of 2-phosphanaphthalene a remarkable expulsion of a phosphours atom is observed.     

The effect of carbonyl substitution on the strain energy of small ring compounds and their six-member ring reference compounds

High level ab initio calculations have been applied to the estimation of ring strain energies (SE) of a series of three- and six-member ring compounds. The SE of cyclohexane has been estimated to be 2.2 kcal/mol at the CBS-APNO level of theory. The SE of cyclopropane has been increased to 28.6 kcal/mol after correction for the one-half of the SE of cyclohexane. The SEs of a series of carbonyl-containing three-member ring compounds have been estimated at the CBS-Q level by their combination with cyclopropane to produce a six-member ring reference compound. The SEs of cyclopropanone (5), the simplest alpha-lactone (6) [oxiranone], and alpha-lactam (7) [aziridinone] have been predicted to be 49, 47, and 55 kcal/mol, respectively, after correction for the SE of the corresponding six-member ring reference compound. The SEs of cyclohexanone, delta-valerolactone, and delta-valerolactam have been estimated to be 4.3, 11.3, and 5.1 kcal/mol, respectively. Marked increases in the SE of silacyclopropane and siladioxirane have been established, while significant decreases in the SEs of phosphorus, sulfur, dioxa- and diaza-containing three-member ring compounds were observed. The ring strain energies of the hydrocarbons (but not heterocycles) exhibit a strong correlation with their C-H bond dissociation energies.     

Mass spectral fragmentation studies in usnic acid and related compounds

A study of the fragmentation patterns of the naturally occurring lichen substance, usnic acid (I) and various other chemically and biochemically derived compounds is reported and discussed. From these results it is demonstrated that the characteristic fragmentation patterns observed are of considerable utility in determining not only the substitution patterns on these highly oxygenated molecules, but also the structural elucidation of new compounds within the series.     

Mass spectral fragmentation pathways in cyclic difluoramino and nitro compounds

The recently synthesized compounds 4, 4-bis(difluoramino)-1-nitropiperidine (I), 1,4,4-trinitropiperidine (II), 1,1,4,4-tetranitrocyclohexane (III), 1,1,4, 4-tetrakis(difluoramino)cyclohexane (IV) and 3,3,7, 7-tetrakis(difluora-mino)octahydro-1,5-dinitro-1,5-diazocine (HNFX, V) are being considered as potential energetic materials. The mass spectra of these compounds were studied using electron ionization (EI) mass spectrometry. A collision-induced dissociation (CID) study of the major EI peaks was carried out using a Finnigan TSQ 700 tandem mass spectrometer. The mass fragmentation pathways are constructed and discussed. The decomposition of HNFX (V), under EI, appeared to parallel the thermal decomposition of nitramines where N-NO(2) cleavage is often the first step. However, the two nitramines with a six-membered ring structure (I and II) underwent initial loss of a geminal substituent; loss of a nitramine nitro group was the secondary step. The two cyclohexane structures (III and IV) showed similar initial fragmentation pathways, featuring successive losses of nitro or difluoramino groups. Copyright 2000 John Wiley & Sons, Ltd.     

Electrophilic substitution in the benzene ring of indole compounds (Review)

Data on the orientation of electrophilic substitution reactions (nitration, halogenation, acylation, and sulfonation) in the benzene ring of indoles are systematized. The effect of protonation on the direction of substitution is examined. The effects of a pyrrole ring and a substituent in the benzene ring on the orientation reactions are compared.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1181–1199, September, 1980.     

Small ring compounds—XXX : Homolytical aromatic substitution and hydrogen abstraction reaction with cyclopropyl radical

Homolytic aromatic substitution and hydrogen abstraction reactions with cyclopropyl radical were carried out to determine the reactivity and ionic character of cyclopropyl radical by examination of the orientation effect, partial rate factor and influence of substituents. By thermal decomposition of biscyclopropaneformyl peroxide in a series of substituted benzenes, the corresponding cyclopropylated benzene derivatives (the mixture of ortho, meta and para isomers) were obtained in moderate yield. In view of the orientation effect and the partial rate factor, the cyclopropyl radical seems to be fairly free from polar effect, and to resemble the phenyl radical more than the common alkyl radical although the cyclopropyl radical has a slightly higher reactivity than the phenyl radical. The relative reactivity of the 2-phenylcyclopropyl radical in the hydrogen abstraction reaction toward the benzylic position of ring-substituted toluenes gave good Hammett's correlation with the slope of + 0·20 suggesting little ionic character in the transition state. This result was in good agreement with the conclusion obtained from homolytic aromatic substitution reaction and with the chemical reactivity to be expected from the non-planar nearly sp²-hybridized conformation of the cyclopropyl radical.     

Mass spectral fragmentation reactions of a therapeutic 4-azasteroid and related compounds

Mass spectra were acquired for a therapeutic 4-azasteroid (dutasteride), and some related compounds, using various ionization conditions (EI, CI, APCI and ESI) in both positive and negative ion modes. The ionization and fragmentation behavior of the compound dutasteride, its precursors and several analogs is reported. Positive atmospheric pressure chemical ionization (APCI+) and positive electrospray ionization (ESI+) produced distinctive collision-induced dissociation (CID) spectra for the respective [MH]+ ions of dutasteride. The spectral differences are attributed to ion populations having either different structures or different internal energy distributions (as a consequence of the method of ionization). Irrespective of their origin, the protonated molecules undergo interesting fragmentation reactions when collisionally activated. The identity of the major fragmentation products was confirmed by accurate mass measurement. The negative APCI mass spectrum of dutasteride displays extensive dehydrohalogenation, apparently due to the thermal component of the APCI process. Some of the resulting radical anions display remarkable stability toward collisional decomposition. Details of the fragmentation behavior for the negative ion species and their relationship to the positive ion results are discussed.     

Mass spectral studies on aryl-substituted N-carbamoyl/N-thiocarbamoyl narcotine and related compounds

Positive ion mass spectral fragmentation of new N-carbamoyl/N-thiocarbamoyl derivatives of narcotine and compounds closely related to it are reported and discussed. The techniques used include electron impact (EI), fast-atom bombardment (FAB), matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) and electrospray ionization tandem mass spectrometry (ESI-MS/MS). Prominent peaks in the mass spectra of these compounds appear to involve C-C bond cleavage beta to the amine nitrogen with loss of the 4,5-dimethoxy(1H)isobenzofuranone moiety from their molecular ions, along with another prominent peak at m/z 382. No molecular ion peaks of these compounds were recorded in EI, whereas intense [M + H]+ ion peaks were observed in FAB and ESI spectra. MALDI also yielded [M + H]+ ion peaks in good agreement with FAB and ESI studies.     

Mass spectrometric study of camptothecin and related compounds

The electron impact mass spectrometric behavior of ten camptothecin analogs (1-10) is described and discussed in detail with the aid of accurate mass measurement and metastable experiment.     

Mass spectral studies on steroidal compounds. VIII—a comparative study of 6- and 7-oxalactones

The mass spectra of three steroidal ring B 7-oxalactones and one 6-oxalactone have been examined and comparison made with previously studied spectra of 6-oxa isomers. Whereas the mass spectra of 6-oxalactones are conspicuous by an intense peak at m/e 318, no such peak was found for 7-oxalactones. On the contrary, the 7-oxalactones showed characteristic [M ? CH₂O]⁺ ions. Thus, mass spectrometry offers an excellent means of differentiating between isomeric 6- and 7-oxa ?-lactones in the cholestane and β-sitostane series. The fragmentation pathways suggested are supported by accurate mass measurement of some of the salient fragment ions.     

Mass spectral study on thiazolo[3,2-a]benzimidazoles. Studies on heterocyclic compounds. IV

Condensation of α-halocarbonyl compounds and 2-mercaptobenzimidazole gives thiazolo-[3,2-a]benzimidazoles. This condensation occurred at the mercapto group of the benzimidazole followed by cyclization to form the thiazole ring. This was confirmed by the examination of the mass spectra of 2- and 3-methylthiazolo[3,2-a]benzimidazoles, 2- and 3-phenylthiazolo[3,2-a]-benzimidazoles, and their derivatives.     

Mass spectral fragmentation pathways in 2,4,6-trinitroaromatic compounds. A tandem mass spectrometric collision induced dissociation study

A collision induced dissociation study of a series of 2,4,6-trinitroaromatic compounds was carried out using a tandem BB mass spectrometer. Fragmentation pathways of the compounds were determined in the electron impact mode. It was found that dominant fragmentation pathways include loss of OH˙ due to an ortho effect and loss of NO˙ due to the formation of resonance-stabilized products.     

喜树碱及其类似物的质谱研究

本文对喜树碱及其类似物进行了质谱研究,阐明了它们在电子轰击下的裂解规律,对同类型新生物碱和药物代谢产物的结构鉴定提供依据。     

Mass spectrometric study of transformed steroids and related compounds

Conclusions The basic pathways of decomposition of acetates of dihydroxyketones and thiolketones of the pregnene series were elucidated.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2505–2510, November, 1973.