Electron impact and chemical ionization mass spectra of 2,2-diphenyl-3-arylcyclobutanone oximes. Formation of ion m/z 167

The electron impact (EI) and chemical ionization (CI) spectra of 2,2-diphenyl-3-aryl cyclobutanone oximes (1–5) are reported. Formation of diphenylmethyl cation at m/z 167 is a major fragmentation process in both EI and CI spectra. Labelling studies established that the hydrogen involved in this rearrangement transfers from the NOH group and not from cyclobutane ring positions. The [M + 3]⁺ ions are formed under CI conditions as a result of C?N double bond reduction. An interesting secondary kinetic isotope effect is observed in the formation of ion e at m/z 183 in both EI and CI spectra. Other characteristic fragmentation pathways occurring in the EI and CI spectra of these compounds are outlined.     

Electron ionization mass spectral studies of bridgehead 7,7‐dimethylnorbornane‐based β‐amino alcohols

The electron ionization (EI) mass spectra of some new bridgehead 7,7‐dimethylnorbornane‐based β‐amino alcohols have been studied and their fragmentation patterns compared with those of isomeric 3,3‐dimethyl derivatives described by us previously. The dimethyl substitution at C7 results in a significant complication of the spectra, although all compounds show a C1–C2 bond cleavage with charge location at the nitrogen atom that leads to the base peak. Thus, two main fragmentation patterns dominated by cyclopentenylimmonium or methyleneimmonium ions are described depending on the position of the amino group in the norbornane framework (C1 or C2, respectively), as well as other secondary routes that can explain the appearance of the less noticeable fragments. Copyright © 2005 John Wiley & Sons, Ltd.     

Das unterschiedliche massenspektrometrische Fragmentierungsverhalten von Lysinmethylester und dessen N,N′-Diacetylderivat. 27. Mitteilung über das massenspektrometrische Verhalten von Stickstoffverbindungen

The Different Behaviour of Lysine Methyl Ester and its N,N′-Diacetyl Derivative under Electron Impact The base peak in the spectrum of lysine methyl ester is due to the fragment ion C₅H₁₀N (m/e 84), for which the cyclic structure g (Scheme 1) is deduced. During its formation from the [M-COOCH₃]-ion an equilibration of both nitrogen atoms takes place (ion c , Scheme 1). The cyclic nature of ion m/e 84 is in agreement with the intensity of the corresponding ions in the spectra of homologues of lysine methyl ester (Fig. 1). Although in comparison with lysine methyl ester ( 1 ) N,N′-diacetyl-lysine methyl ester ( 7 ) shows the same general fragmentation pathway with formation of the ions [M-COOCH₃] and [M-COOCH₃-H₂NCOCH₃] (m/e 126), the exact fragmentation mechanism proves to the different. Two mechanisms are discussed for the formation of the ion m/e 126 from 7 (Schemes 2 and 3). The results are based on the spectra of labelled derivatives.     

Rearrangement reactions of the molecular ions of some substituted aliphatic oxiranes

The fragmentation reactions of glycidic methyl ester (1) and of its derivatives (2–6) substituted by one, two and three methyl groups, respectively, at the oxirane ring, of the corresponding glycidols (7–12), and of the glycidyl ethers (13–16) in the 70 eV mass spectra have been studied using isotopic labelling and mass-analysed ion kinetic energy spectrometry. It is shown that the typical reaction of these aliphatic oxirane radical cations carrying a nucleophilic methoxy group and hydroxy group, respectively, at the side chain corresponds under high-energy conditions to a rearrangement by a methoxy group or a hydroxy group migration to the β-carbon atom of the oxirane moiety. This rearrangement is very likely mediated by the isomerization of the molecular ions into distonic ions via C? C bond cleavage within the oxirane ring.     

Mass spectrometry in structural and stereochemical problems—CC A study of the fragmentation processes of some pyrilium salts

The principal mode of fragmentation, at both 70 and 15 eV, of pyrilium iodides (I to V) which are substituted by at least one methyl group is the elimination of hydrogen iodide from the non-detectable molecular ion. In contrast the mass spectrum (Fig. 6) of 2,4,6-triphenyl pyrilium iodide (VI) shows its dominant fragmentation to be due to the loss of an iodine atom from the molecular ion. The mass spectra (for example Figs. 6 and 7) of 2,4,6-triphenyl pyrilium iodide, bromide and tetrafluoroborate (VI, VII and VIII) are virtually identical except for the peaks corresponding to a molecule of iodine (m/e 254), hydrogen iodide (m/e 128) and iodine (m/e 127) in the mass spectrum (Fig. 6) of the iodide. Other fragmentation routes common to these pyrilium salts are described.     

Identification of esters by collisional charge inversion of their enolate ions

The collisional charge inversion and neutralization-reionization (^?NR) mass spectra of the enolate ions of m/z 115 derived from the four butyl acetates, the two propyl propionates, ethyl butyrate, ethyl isobutyrate, methyl valerate, methyl 2-methylbutyrate and methyl 3-methylbutyrate were recorded. The major primary fragmentation reactions of the unstable carbenium ion formed by charge inversion involve elimination of an alkoxy radical to form a ketene or alkylketene molecular ion and formation of an alkyl ion consisting of the R¹ group of RCOOR¹. A minor fragmentation reaction involves elimination of an alkyl radical by cleavage of a C? C bond α to the ether oxygen. The alkylketene ions fragment by β-cleavage eliminating an alkyl radical to form an olefinic acylium ion. In most cases the charge inversion mass spectra of the enolate ions allow identification of the ester.     

Influence of substituent groups at the 3‐position on the mass spectral fragmentation pathways of cephalosporins

The structural fragment ions of nine cephalosporins were studied by electrospray ionization quadrapole trap mass spectrometry (Q‐Trap MSⁿ) in positive mode. The influence of substituent groups in the 3‐position on fragmentation pathway B, an α‐cleavage between the C7? C8 single bond, coupled with a [2,4]‐trans‐Diels‐Alder cleavage simultaneously within the six‐membered heterocyclic ring, was also investigated. It was found that when the substituent groups were methyl, chloride, vinyl, or propenyl, fragmentations belonging to pathway B were detected; however, when the substituents were heteroatoms such as O, N, or S, pathway B fragmentation was not detected. This suggested that the [M–R₃]⁺ ion, which was produced by the bond cleavage within the substituent group at the 3‐position, had a key influence on fragmentation pathway B. This could be attributed to the strong electronegativity of the heteroatoms (O, N, S) that favors the production of the [M–R₃]⁺ ion. Moreover, having the positive charge of the [M–R₃]⁺ ion localized on the nitrogen atom in the 1‐position changed the electron density distribution of the heterocyclic structure, which prohibits a [2,4]‐reverse‐Diels‐Alder fragmentation and as a result fragmentation pathway B could not occur. The influence of the substituent group in the 3‐position was determined by the intensity ratio (e/d) of ions produced by fragmentation pathway A, a [2,2]‐trans‐Diels‐Alder cleavage within the quaternary lactam ring, including the breaking of the amide bond and the C6? C7 single bond (ion d), and fragmentation pathway B (ion e). The results indicate that the electronegativity of the substituent group was a key influencing factor of pathway B fragmentation intensity, because the intensity ratio (e/d) is higher for a chlorine atom, a vinyl, or a propenyl group than that of a methyl group. This study provided some theoretical basis for the identification of cephalosporin antibiotics and structural analysis of related substances in drugs. Copyright © 2010 John Wiley & Sons, Ltd.     

Reversible cyclomerization and long range hydrogen abstraction by electron impact of 7-coumarinyl diesters ROOC(CH2)nCOOR

The mass spectra of 4-methyl-7-coumarinyl and 7-coumarinyl diestes ROOC(CH₂)_nCOOR (n = 2-12) have ben studied by appearance potential measurements, deuterium labelling and by comparison with suitable reference compounds such as the mised diestes ROOC(CH₂)_nCOOR′ (R=4-methyl-7-coumarinyl and R′ = methyl and phenyl) and 3.4-dihydro-4-methyl-coumarinyl diestes. Observations on the fragment ions of m/e 324, produced from the 7-coumrinyl diestes and their photocyclomers, by elimination of the central bridge as O?C?CH? (CH₂)_n–2? CH?C?O, demonstrate the existence and reversible formation of cyclomeric molecular ions. A stable bound system between the coumrin end groups is formed only at high internal energies by expulsion of a hydrogen atom, followed by elimination of the central bridge from the [M? H]⁺ ion. It is also shown that the lifetime of the open form molecular ions decreases remarkably for chain lengths with n larger than 6.     

Regioselective synthesis of o-triazolyl-1,5-benzodiazepin-2-ones and o-isoxazolyl-1,5-benzodiazepin-2-ones via copper-catalyzed 1,3-dipolar cycloaddition reactions

A series of novel O-triazolyl-1,5-benzodiazepin-2-ones 6a–o and O-isoxazolyl-1,5-benzodiazepin-2-ones 7a–o was synthesized via a Cu(I)-catalyzed 1,3-dipolar alkyne–azide coupling reaction of N-substituted-1,5-benzodiazepine–alkyne derivatives 3a–c with various aromatic azides 4a–e and nitrile oxides 5a–e, respectively. The chemical structures of synthesized compounds were determined using ¹H NMR, ¹³C NMR, heteronuclear multiple bond correlation (HMBC), high-resolution mass spectra, as well as elemental analysis and was further confirmed by an X-ray diffraction analysis for compound 7d.     

The high resolution mass spectra of α,β-unsaturated and α-chloromercuri-α,β-unsaturated steroidal ketones

The high resolution mass spectra (500 eV) of some α,β-unsaturated steroidal ketones have been studied and compared with the spectra of the corresponding α-chloromercuri ketones. In the latter, the carbon-mercury bond frequently remains intact at the expense of the fission of two carbon-carbon bonds. The abundance of mercury-containing ions allows the use of the mercury atom fingerprint in confirming ring B fragmentation of the steroid nucleus at C(6)–C(7) and C(9)–C(10) for 5α-androst-1-ene-3,17-dione, 1,4-androstadiene-3,17-dione and their 2-chloromercuri derivatives; and at C(7)–C(8) and C(9)–C(10) for 1,4,6-androstatriene-3,17-dione, 1,4,6-androstarien-17 β-ol-3-one and their 2-chloromercuri derivatives. 2-Chloromercuri-1,4,6-androstatriene-3,17-dione and 2-chloromercuri-1,4,6-androstatrien-17 β-ol-3-one also give an abundant ion as the result of ring C fragmentation at C(8)–C(14) and C(11)–C(12), the chloromercuri group being replaced by a hydrogen atom. This ring C cleavage gives the only recognizable distinctive fragmentation ion for 1,4,6-pregnatriene-3,20-dione and 2-chloromercuri-1,4,6-pregnatriene-3,20-dione. For most of the mercurated steroids, the low resolution mass spectra (70 eV) are reported. In these spectra, the fragmentation patterns are similar to those obtained using the higher ionization energy employed for the high resolution spectra.     

Pteridines. Part LXXXV. Chemical synthesis of deoxysepiapterin and 6-acylpteridines by acyl radical substitution reactions

A new synthesis of deoxysepiapterin ( 2 ), one of the two yellow eye pigments of the Drosophila mutant sepia, is described. The synthetic approach makes use of a homolytic nucleophilic acylation of 7-(alkylthio)pteridine derivatives ( 11, 13, 15, 18, 20 ) leading to the corresponding 6-acyl derivatives ( 21–27 ). Desulfurizations have been achieved for the first time in the pteridine series using Raney-Co,Raney-Cu, or Cu? Al alloy in alkaline medium. Besides cleavage of the C(7)? S bond, further reductions of the C?O group at C(6) and the C(7)?N(8) bond are detected as side reactions leading to 6-(1-hydroxyalkyl) ( 34, 35, 42, 43 ) and 6-acyl-7,8-dihydro derivatives ( 2, 36, 37 ), respectively, The newly synthesized compounds have been characterized by elemental analysis, p_K determination, UV and ¹H-NMR spectra.     

Massenspektrometrische Untersuchungen an Organophosphorverbindungen. II—Elektronenstoßinduzierte Fragmentierungen von Tetraorganodiphosphandisulfiden

The behaviour under electron impact (70 eV) which includes some rearrangement processes of some tetraorganodiphosphanedisulfides R₂P(S)-P(S)R₂ (R ? CH₃, C₂H₅, n-C₃H₇, n-C₄H₉, C₃H₅, C₆H₅) and CH₃RP(S)–P(S)CH₃R (R ? C₂H₅, n-C₃H₇, n-C₄H₉, C₆H₅, C₆H₅, C₆H₅,CH₂) is reported and discussed. Fragmentation patterns which are consistent with direct analysis of daughter ions and defocusing metastable spectra are given. The atomic composition of many of the fragment ions was determined by precise mass measurements. In contrast to compounds R₃P(S) loss of sulphur is not a common process here. The first step in the fragmentation of these compounds is cleavage of one P–C bond and loss of a substituent R?. The second step is elimination of RPS leading to [R₂PS]⁺ from which the base peaks in nearly all the spectra arise. The phenyl substituted compounds give spectra with very abundant [(C₆H₅)₃P]^+. and [(C₆H₅)₂CH₃P]^+. ions respectively, resulting from [M]^+. by migration of C₆H₅. Rearrangement of [M]^+. to a 4-membered P-S ring system prior to fragmentation is suggested.     

Electron impact fragmentation of some cyclohexyl thiophosphororganic amides

This paper presents the mass spectra, fragmentation pathways and structures of ions obtained by electron impact from methyl cyclohexyl phosphinomorpholinylamidothioate (1), cyclohexyl phosphonomorpholinylamidochloridothioate (2), cyclohexyl morpholinylamidophosphonothioic acid (3) and O-methyl cyclohexyl phosphonomorpholinylamidothioate (4). The fragmentation pathways and ion structures were established by exact mass determinations on compound 1 and by metastable transitions of all the compounds.     

Electron ionization mass spectral fragmentation of C19 isoprenoid aldehydes and carboxylic acid methyl and trimethylsilyl esters

The electron ionization (EI) mass spectra of saturated and alpha,beta-unsaturated C(19) isoprenoid aldehydes and carboxylic acid methyl and trimethylsilyl esters are reported. Different pathways are proposed in order to explain the main fragmentations observed. The conjugated double bond migrates more or less readily before gamma-hydrogen rearrangement according to the structure of the considered compound. Configurations of the double bond of alpha,beta-unsaturated C(19) isoprenoid aldehydes and fatty acid methyl and trimethylsilyl esters can be easily determined thanks to the peaks at m/z 97, 127 and 185, respectively, which are much more abundant in the mass spectra of the Z isomers owing to the formation of a cyclic ion. In the case of trimethylsilyl esters, subsequent fragmentation of the cyclic ion at m/z 185 affords two other diagnostic ions at m/z 95 and 169.     

STUDIES OF HETEROCYCLIC COMPOUNDS: VI1 THE MASS SPECTRA OF SOME 2-THIOPHENEMERCURIC DERIVATIVES

Abstract

The mass spectra of some 2-thiophenemercuric derivatives are determined and the fragmentation interpretations are based on mechanistic analogy and supported in some cases by metastable peaks and low energy mass spectra. They all fragment ultimately to the 2-thienyl cation formed either through a two-step process, by cleavage of Hg[sbnd]X bond to give the 2-thienylmercuric cation, followed by extrusion of mercury, or by a one-step process through cleavage of carbon-mercury bond. Their base peaks being the C₃H₃ ⁺ion (m/e 39).     

Characterization of five [C4H7O]+ Ion structures. Fragmentation of the 2-pentanone molecular ion

The [C₄H₇0]⁺ ions [CH₂?CH? C(?OH)CH₃]⁺ (1), [CH₃CH?CH? C(?OH)H]⁺ (2), [CH₂?C(CH₃)C(?OH)H]⁺ (3), [Ch₃CH₂CH₂C?O]⁺ (4) and [(CH₃)₂CHC?O]⁺ (5) have been characterized by their collision-induced dissociation (CID) mass spectra and charge stripping mass spectra. The ions 1–3 were prepared by gas phase protonation of the relevant carbonyl compounds while 4 and 5 were prepared by dissociative electron impact ionization of the appropriate carbonyl compounds. Only 2 and 3 give similar spectra and are difficult to distinguish from each other; the remaining ions can be readily characterized by either their CID mass spectra or their charge stripping mass spectra. The 2-pentanone molecular ion fragments by loss of the C(1) methyl and the C(5) methyl in the ratio 60:40 for metastable ions; at higher internal energies loss of the C(1) methyl becomes more favoured. Metastable ion characteristics, CID mass spectra and charge stripping mass spectra all show that loss of the C(1) methyl leads to formation of the acyl ion 4, while loss of the C(5) methyl leads to formation of protonated vinyl methyl ketone (1). These results are in agreement with the previously proposed potential energy diagram for the [C₅H₁₀O]⁺˙ system.     

Field ionization mass spectrometry of higher n-alkenes

In a strong electric field the molecular ions of n-alkenes ≤C-12 decompose via cleavage of the C? C bond β to the double bond to form the characteristic alkenyl ions that may be used for the identification of positional isomers. For 3-alkenes (>C-10), 4-, 5- and 6-alkenes the formation of the ions with m/e 54 via double β-cleavage is typical. The field ionization mass spectra of the cis and trans isomers are indistinguishable.     

Mass spectra of new heterocycles: IX. Main fragmentaion laws of 7-methyl-2-(methylsulfanyl)-3-(1-ethoxyethoxy)-4,5-dihydro-3<Emphasis Type="Italic">H</Emphasis>-azepine and its structural isomers (2,3-dihydropyridine,pyrrole, thiophene) under electron impact

Mass spectra were investigated for the first time of four structural isomers of heterocycles, formerly inavailable 7-methyl-2-(methylsulfanyl)-3-(1-ethoxyethoxy)-4,5-dihydro-3H-azepine, 2,2-dimethyl-6-(methylsulfanyl)-5-(1-ethoxyethoxy)-2,3-dihydropyridine, 1-isopropyl-2-(methylsulfanyl)-3-(1-ethoxyethoxy)pyrrole, and N-isopropyl-N-methyl-3-(1-ethoxyethoxy)-2-thiophenamine prepared from a single linear precursor, adduct of α-lithiated 1-(1-ethoxyethoxy)allene and isopropyl isothiocyanate. All compounds formed a molecular ion (I _rel 1–6%) whose primary fragmentation at the electron impact (70 eV) occurs in two principal directions related to the cleavage of the C-O bonds in the 1-ethoxyethoxy-substituent: with a simple rupture of the bonds C-OEt and C-O(heterocycle) and with the elimination of an ethoxyethene molecule. In the spectra of 4,5-dihydro-3H-azepine and 2,3-dihydropyridine the first fragmentation channel of [M]^+· dominates. The second direction prevailes at the fragmentation of pyrrole and thiophene molecular ions leading to an odd-electrons ion with m/z 171. Further fragmentation of this ion is characteristic of each isomer and resulted in the formation of diagnostic ions providing a possibility of identification of these isomers by mass spectrometry.     

Mass spectra of some 1-substituted-4-acetoacetyl-3-methylpyrazol-5-ols

The fragmentation of 1-phenyl-, l-(2′-pyridyl)- and 1-(4′-methyl-2′-quinolyl)-4-acetoacetyI-3-methyIpyrazol-5-ols (compounds 1, 2 and 3, respectively) on electron impact has been studied and the major processes interpreted. The common feature in the mass spectra of these compounds is the loss of ketene, acetonyl radical, acetone and two molecules of ketene from the molecular ion. Whereas the ion generated after the last process, which corresponds to 1-substituted-3-methyIpyrazol-5-ols, loses methyl cyanide in the case of 1, similar ions in the case of 2 and 3 lose ?₂HO moiety, necessitating an intramolecular hydrogen transfer followed by ring fission and subsequent loss of methyl cyanide. All these and other related processes have been substantiated with the help of accurate mass measurements of the fragment ions and B/E linked-scan spectra.     

13,14-Seco-steroids: A New Type of Modified Steroids Containing a Nine-Membered Ring

Oxidations of 14α-hydroxy-5α-cholestan-3β-yl acetate ( 5 ) with lead tetraacetate under thermal or photolytic conditions or in the presence of iodine proceed mainly by fragmentation of the C(13)−C(14) bond to give as the primary products the 13,18-didehydro-13,14-seco derivative 6 and the (E )-Δ¹²-13,14-seco ketone 11 , respectively. Further transformations of these compounds under conditions of their formation afforded, in addition, the acetoxy derivatives 7 – 9 (from 6 ), and the D-homo-C-nor compound 12 and (12R,13R)-epoxide 13 (from 11 ). Unexpectedly, the photolytic lead-tetraacetate oxidation of 5 resulted partly (to ca. 20%) in a reversible fragmentation involving scission and recombination of the C(8)−C(14) bond followed by formation of the 14β,22-ether 10 . Possible mechanisms for the observed transformations are discussed.