Electron-impact-induced ion fragmentation of polyfunctional N-cyclohexylcarbamates

Mass spectra at 70, 15 and 10 eV are reported for methyl N-cyclohexylcarbamate, methyl N-trans-2-iodocyclohexylcarbamate, allyl N-cyclohexylcarbamate and allyl N-trans-2-iodocyclo-hexylcarbamate. Principal modes of ion fragmentation including hydrogen and skeletal rearrangements are discussed in terms of individual functional groups and their interaction, and are consistent in many cases with mechanisms previously proposed for other compounds. The effects of the iodo and the allyl groups, when present, predominate in the spectra. The application of McLafferty's ‘active site’ concept to these polyfunctional compounds is found to be useful.     

Electron-impact-induced fragmentation of some diterpenoid acetals

Study of the low and high-resolution mass spectra of a series of diterpenoid acetals, including both positional isomers and stereoisomers, has permitted the proposal of some characteristic fragmentation pathways leading to analytically distinctive peaks. The mass spectrum was particularly informative in the assignment of structure to an unexpected rearrangement product (V).     

Electron-impact-induced fragmentation of some phthalazinone derivatives

The mass spectra of 4-(ω-hydroxyalkylamino)-phthalazinone derivatives (I to IV) have been studied. The most important primary fragmentation process is the fission of the alkyl chain β to the amino group, combined with an intramolecular cyclisation reaction. This process results an ion of tricyclic structure, possessing a 4-membered ring, as was established by partial ¹⁵N labelling.     

Electron-impact-induced fragmentation of morellin and related compounds

The mass spectra of morellin and other related natural products, isolated from the various Garcinia species, have been recorded and the data has been rationalised. The characteristic cleavage is the opening of the bicyclo(2.2.2) octenone ring system by a retro-Diels-Alder reaction. The γ-pyrone ring also undergoes the retro-Diels-Alder fragmentation. These two modes of cleavage indicate the different substituents on the main skeleton of morellin. The hydrogenated derivatives show slight variations in their fragmentation modes. The mass spectral data assists considerably in the structural elucidation of similar complex molecules, if isolated in minute quantities.     

Palladium‐mediated polymerization of cyclic diazoketones

Palladium‐mediated polymerization of cyclic diazoketones was investigated. Although cyclic diazoketones 1a,b derived from cyclohexanone and 1‐tetralone did not homopolymerize, they can be used as a comonomer for copolymerization with polymerizable acyclic diazoketones. On the other hand, an α,β‐unsaturated cyclic diazoketone 2a prepared from 2‐cyclohexen‐1‐one polymerized to give a polymer poly 2a ′ with M_n = 1400 in a 23.8% yield. Addition of some nucleophiles to C?C bond in poly 2a ′ was carried out. Copolymerization of 2a and its dimethyl‐substituted analogues 2b,c with acyclic diazoketones was also investigated. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1638–1648, 2008     

Electron-impact-induced fragmentation of some isomeric cyclopropyl picolyl and pyridyl ketones

The electron-impact-induced fragmentation of three cyclopropyl picolyl ketones and three cyclopropyl pyridyl ketones has been studied with the aid of deuterium labeling, high resolution mass measurements and metastable mode operation.     

Mass spectrometry in structural and stereochemical problems-CCXXIX: Electron-impact-induced fragmentation of boric acid esters

The mass spectral decompositions of cyclic and acyclic borates have been examined. Straight chain trialkyl borates fragment by C? O cleavage reactions accompanied by transfer of one or two hydrogen atoms, whereas tri-(sec-alkyl) borates primarily undergo α-cleavage reactions. Both types of cleavage are observed in the fragmentation of cyclic borates. B? O bonds are not broken in the formation of most major fragment ions. The fragmentations of borates are compared with those of phenylboronates with special emphasis on the rearrangements leading to hydrocarbon ions in the spectra of the latter.     

Mass spectra of organoarsenic compounds. III—Electron-impact-induced fragmentation of trialkylarsenates and penta-alkoxyarsoranes

The mass spectra of a series of trialkylarsenates are reported, together with those of dimethyl methylarsonate, pentamethoxyarsorane and pentaethoxyarsorane. Their behaviour under electron-impact is discussed and compared with that reported for trialkylphosphates.     

Mass spectra of organoarsenic compounds—II: Electron-impact-induced fragmentation of 2-substituted-1,2,2-dioxarsenanes

The electron-impact-induced fragmentation of 2-substituted 1,3,2-dioxarsenanes has been studied. The main fragmentation modes have been determined with the use of high resolution mass measurements and by application of the metastable defocusing technique. The predominant fragmentation for the 2-alkyl-1,3,2-dioxarsenanes proceeds via the loss of the 2-substituent from the molecular ion. In the case of 2-phenyl-1,3,2-dioxarsenanes elimination of the phenyl group competes with the formation of a C₆H₅ As ion as well as loss of aldehyde from the molecular ions.     

Electron-impact-induced rearrangement of organic hypophosphates

Preliminary investigation of electron-impact behavior of organic hypophosphates and their mono and dithio derivatives has shown that they undergo skeletal rearrangement to the anhydride type of structure ,and that this anti-Arbuzov rearrangement is of electron-impact origin.     

The electron-impact-induced fragmentation of aromatic aldoximes: I

Primary fragmentations of benzaldoxime include loss of H·, OH·, HCN, CO and HCNO and this paper discusses the first three losses. The previously reported losses of H₂O and O were proven to be thermal in origin. Information about the investigated fragmentations was obtained from the deuterated analogues and their metastable characteristics. The OH· elimination is complex. The loss of HCN exhibits a metastable with a composite structure. This fragmentation may occur both via a 4-centred and 5-centred mechanism. A fluorine atom at the ortho position of the phenyl ring favours the 5-centred mechanism.     

Mass spectrometry of heterocyclic compounds—III. Electron-impact-induced fragmentation of 1,2-benzisothiazole and some 3-substituted derivatives

The mass spectra of fifteen 1,2-benzisothiazoles are reported; their fragmentation patterns have been investigated by labelling experiments, high resolution mass measurements and defocused metastable ion detection. The parent compound of the series, 1,2-benzisothiazole, eliminates HCN after partial inter-ring hydrogen scrambling. The extent of scrambling has been determined for normal daughter ions produced at different electron beam energies and also for metastable daughter ions, and is compared with the data reported for benzothiazole. Some 3-substituted derivatives show unusual fragmentation patterns. The mechanisms of these processes are under further investigation.     

Decomposition of diazoketones in organic sulfides and sulfoxides: Cyclopropane formation from diazoketones via sulfonium ylides

The catalytic decomposition of diazoketones in the presence of organic sulfides and sulfoxides, gives sulfonium and sulfoxonium ylides as the primary reaction products, the final products isolated depending upon the relative nucleophilicity of the sulfides compared to that of the corresponding ylides, and on the stability of the ylides. The mechanism, scope and limitations of a new method of cyclopropane formation from diazoketones are discussed. Some circumstantial evidence supporting a concerted process for Wolff rearrangement is presented.     

Organoaluminum‐mediated polymerization of diazoketones

Polymerization of diazoketones mediated by organoaluminum compounds was investigated. Trialkylaluminum R₃Al (R = iBu, Et, Me) and diisobutylaluminum hydride (DIBAL) polymerized (E)‐1‐diazo‐3‐nonen‐2‐one ( 1 ) to give polymers with M_n = 2000–3500, which contained nearly 33 mol % of azo group (? N?N? ) along with the dominant acylmethylene unit in the main chain. On the other hand, when (E)‐1‐diazo‐4‐phenyl‐3‐buten‐2‐one ( 2 ) was used as a monomer for the organoaluminum‐mediated polymerization, the resulting polymers had ethylidene (? CH[CH₃]? ) units in the main chain along with acylmethylene and azo group, as a result of reductive cleavage of the acyl group during the polymerization. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5209–5214, 2007     

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.     

Electron-impact-induced anisotropic etching of silicon by hydrogen

The etch rate of silicon in a hydrogen low-pressure discharge plasma can be strongly enhanced by electron bombardment, reaching presently up to 1000 Å/min. The etch rate increases linearly with increasing electron current density and hydrogen pressure (range 0.05–0.7 mbar) and decreases with increasing temperature, yielding an activation energy of –4.2 kcal/mole in a temperature range of 80 to 300°C. The etching remains anisotropic within the whole pressure range studied.     

Mass spectrometry in structural and stereochemical problems. CCXXXVII—Electron-impact-induced hydrogen losses and migrations in some aromatic amides

The mass spectra of a series of benzamides and naphthamides have been investigated with respect to their propensity to lose an aromatic hydrogen atom from their molecular ions. Deuterium labeling and a study of model compounds have led to a plausible mechanistic rationalization for the formation of the [M — 1] ions. The other principal fragmentation processes observed with these compounds are discussed, including the specificity of a previously uninvestigated rearrangement process.     

A ring fragmentation approach to medium-sized cyclic 2-alkynones

Bicyclic γ-silyloxy-β-hydroxy-α-diazoketones, in which the Cβ-Cγ bond is the ring fusion bond, productively fragment when treated with tin(IV) chloride to provide medium-sized cyclic 2-alkynones. This method provides good to excellent yields of 10-, 11-, and 12-membered alkynone products.