bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rearrangements of ionized carbonyl compounds
Authors: McAdoo David J. 
Published: May 2005

AbstractDevelopments in our knowledge of the isomerizations of low‐energy [CnH2nO]+˙ and [CnH2nO2]+˙ ions are traced. The reactions of these ions take place by a series of simple steps common to them all. This article represents an extension of the lifelong efforts of Professor McLafferty to provide a unified understanding of the reactions of ions in the gas phase.
Gas‐phase alkylation of 2‐methylfuran under chemical ionization conditions
Authors: Robin D. , Hoppilliard Y. , Audier H. 
Published: May 2005

AbstractIn the gas phase, under chemical ionization conditions, the sites of attachment of [CH3]+ and [C2H5]+ to 2‐methylfuran have been studied by tandem mass spectrometry. Spontaneous metastable and collision‐induced fragmentations have been compared to those observed for the protonated alkylfuran isomers. The results obtained show that alkylation occurs preferentially at the β‐position.
Charge localization by molecular orbital calculations. II. Formamide, thioformamide and N‐methylated analogues
Authors: Baldwin Michael A. , Welham Kevin J. 
Published: May 2005

AbstractAb initio molecular orbital calculations have been used to determine the degree of charge localization associated with the formation of radical cations on electron impact of formamide, thioformamide and their N‐methyl and N, N‐dimethyl analogues. The charge favours the nitrogen of formamides and the sulphur of thioformamides, but the degree of localization is calculated to be lower than in the radical cations of urea and thiourea.
Selective reagents in chemical ionization mass spectrometry: Tetramethylsilane with ethers
Authors: Orlando Ron , Ridge D. P. , Munson Burnaby 
Published: May 2005

AbstractChemical ionization mass spectra of several ethers obtained with He/(CH3)4Si mixtures as the reagent gases contain abundant [M + 73]+ adduct ions which identify the relative molecular mass. For the di‐n‐alkyl ethers, these [M + 73]+ ions are formed by sample ion/sample molecule reactions of the fragment ions, [M + 73 − CnH2n]+ and [M + 73 − 2CnH2n]+. Small amounts of [M + H]+ ions are also formed, predominantly by proton transfer reactions of the [M + 73 − 2CnH2n]+ or [(CH3)3SiOH2]+ ions with the ethers. The di‐s‐alkyl ethers give no [M + 73] + ions, but do give [M + H]+ ions, which allow the determination of the relative molecular mass. These [M + H]+ ions result primarily from proton transfer reactions from the dominant fragment ion, [(CH3)3SiOH2]+ with the ether. Methyl phenyl ether gives only [M + 73]+ adduct ions, by a bimolecular addition of the trimethylsilyl ion to the ether, not by the two‐step process found for the di‐n‐alkyl ethers. Ethyl phenyl ether gives [M + 73]+ by both the two‐step process and the bimolecular addition. Although the mass spectra of the alkyl etherr are temperature‐dependent, the sensitivities of the di‐alkyl ethers and ethyl phenyl ether are independent of temperature. However, the sensitivity for methyl phenyl ether decreases significantly with increasing temperature.
Enhanced positive secondary ion emission from substituted polynuclear aromatic hydrocarbon/sulfuric acid solutions
Authors: Leibman Christopher P. , Todd Peter J. , Mamantov Gleb 
Published: May 2005

AbstractSecondary ion mass spectra of singly substituted aromatic hydrocarbon/H2SO4 solutions showed intense aromatic molecular ion and protonated aromatic molecule peaks characteristic of dissolved aromatic compounds from a number of aromatic compound classes, including acids, aldehydes, ketones, nitriles and nitrogen heterocycles. The presence of simultaneously abundant peaks for molecular ions and protonated molecules in secondary ion mass spectra of each aromatic compound/sulfuric acid solution is consistent with known or expected gas‐phase proton transfer chemistry. The ratio of intensities, M+˙:[M + H]+, appears to be determined by sulfuric acid solution chemistry of the compound. Spectra obtained from 1–2 μl samples were relatively free from chemical noise and persisted for up to 20 min. Detection limits for some substituted aromatic compounds are estimated to be 10−12.
Unidirectional triple and double hydrogen rearrangement reactions in the radical cations of γ‐arylalkanols
Authors: Kuck Dietmar , Filges Ulrich 
Published: May 2005

AbstractA novel fragmentation reaction accompanied by the unidirectional migration of three hydrogen atoms has been found in the radical cations of γ‐arylpropanols with electron‐donating substituents in the para position. This triple hydrogen (3H) rearrangement reaction is the dominant fragmentation channel of the long‐lived molecular ions of trans‐2‐(4′‐dimethylaminobenzyl)‐l‐indanol, 2, but it occurs also in simpler γ‐arylpropanol ions. Deuterium labelling of 2 reveals that the three hydrogen atoms originate with extraordinarily high specificity from the C(l), C(2) and O positions of the alcohol moiety. Cis‐ and 3′‐substituted isomers do not undergo this reaction. Along with the 3H rearrangement reaction a unidirectional double hydrogen (2H) rearrangement reaction takes place independently and with less specificity in the trans‐2‐(4′‐X‐benzyl)‐l‐indanol ions 1+˙ and 2+˙. No hydrogen exchange occurs during the 3H and 2H rearrangement reactions. Mechanistic alternatives of these unusual fragmentation reactions are discussed; the experimental evidence strongly favours pathways via several intermediate ion–neutral complexes.
Stabilization of even‐electron ions by cyclization of substituents on 3N‐ and 4N‐nitrogens in 4N‐substituted cytosines
Authors: Plaziak Adam S. , Celewicz Lech , Spychala Jaroslaw , Golankiewicz Krzysztof 
Published: May 2005

AbstractElectron impact mass spectra of 4N‐substituted derivatives of cytosine are reported. The strong influence of 4N‐substituents on the mode of mass fragmentation occurring upon electron impact ionization was proved. The presence of α‐carbon in the 4N‐substituent extends the possibilities of fragmentation via rearrangement leading to formation of even‐electron bicyclic ions containing quaternary 3N‐nitrogen. When β‐carbon was present in the 4N‐substituent, the decomposition based on elimination of alkenes was detected as well as the rearrangement leading to formation of bicyclic even‐electron ions containing quaternary 3N‐ or 4N‐nitrogen.
A gas‐phase anionic analog of the wittig reaction. An ion cyclotron resonance study of the gas‐phase ion chemistry of silyl carbanions
Authors: Campanaro A. , Marvin C. H. , Morehouse S. P. , McMahon T. B. 
Published: May 2005

AbstractGas‐phase ion–molecule reactions of a variety of fluorosilyl carbanions with compounds containing double bonds to oxygen, XO, have been examined using pulsed ion cyclotron resonance spectroscopy. The predominant reaction channel observed for species not containing acidic hydrogens is a Wittig‐like process involving SiO bond formation and elimination of XCH2 species. The gas‐phase acidity of F3Si(CH3) has been determined and those of F2Si(CH3)2 and FSi(CH3)3 have been estimated. From the fluoride transfer reactions of F3SiCH2− the fluoride affinity of F2SiCH2 has been estimated and limits on the π bond strength in this silaethene obtained. Potential analytical applications of the Wittig reactivity have been discussed.
Mass spectra of halogenated esters: 8. Methyl esters of 2,3‐dichloro‐, bromochloro‐ and dibromopropenoic acids
Authors: Korhonen Ilpo O. O. 
Published: May 2005

AbstractThe mass spectral fragmentation of methyl esters of E and Z isomers of 2,3‐dichloro‐, 2‐bromo‐3‐chloro‐, 3‐bromo‐2‐chIoro‐ and 2,3‐dibromopropenoic acids have been investigated. The M+˙ peak is shown with all isomers, the [M − OCH3]+, [M − X]+, [M − OCH3 − CO]+, [M − OCH3 − CO − X]+˙ and [M − OCH3 − CO − X − X]+ ions constituting abundant peaks in all spectra. The results, particularly from the bromochloro isomers, show that a halogen atom is eliminated from the 3‐ rather than the 2‐ position and from the Z rather than the E isomer. Bromine as a bulky atom is preferentially lost.
Electron impact fragmentation of isomeric 2‐diazo‐2‐cyanoacetamides and 4‐cyano‐5‐hydroxy‐l,2,3‐triazoles
Authors: Lebedev Albert T. , Alekseeva Tatiana N. , Bakulev Vasiliy A. , Kolobov Mikhail Yu. , Petrosyan Valeriy S. 
Published: May 2005

AbstractOn the basis of electron impact mass spectra, high‐resolution mass spectra and metastable ion spectra, the isomerization of the molecular ions of N‐aryl‐2‐diazo‐2‐cyanoacetamides and 1‐aryl‐4‐cyano‐5‐hydroxy‐l,2,3‐triazoles into each other or into the common structure has been demonstrated. Corresponding N‐cyclohexyl derivatives are unable to undergo such a transformation.
Identification of platelet activating factor by tandem mass spectrometry
Authors: Plattner Ronald D. , Stack Robert J. , Al‐Hassan Jassim M. , Summers Brent , Griddle Richard S. 
Published: May 2005

AbstractPlatelet activating factor, a phospholipid (1‐O‐alkyl‐2‐O‐acetyl‐sn‐glycerophosphocholine), is a potent mediator of inflammation and acute hypersensitivity reactions. Chemical ionization mass spectra provide useful information for confirmation of structure. However at low levels the confirmation of structure in biological samples is difficult because the chemical noise level is too great. Collisionally activated decomposition daughter spectra of the protonated molecule and major fragment ions of authentic standards were recorded and are discussed. Selected tandem mass spectral scans provided the improvement in signal‐to‐noise to allow positive confirmation of structure at nanogram levels in partially purified extracts from a biological source, the epidermal cell secretions of the saltwater catfish Arius thalassinus.
Mass spectrometric investigation of substituted 1,3‐emthiolaneS‐oxides
Authors: Bortolini O. , Traldi P. , Licini G. 
Published: May 2005

AbstractThe electron impact mass spectrometry of four model 2‐phenyl‐2‐alkyl‐l,3‐dithiolaneS‐oxides is described and discussed with the aid ofB/Emass‐analysed ion kinetic energy collisional spectroscopy and labelling experiments, as well as of fast atom bombardment spectra. The mechanisms of the common fragmentation patterns are given.
Characterization of cyclotrimethylenetrinitramine (RDX) by N,H isotope analyses with pyrolysis–atmospheric pressure ionization tandem mass spectrometry
Authors: Snyder A. Peter , Kremer Johannes H. , Liebman Shirley A. , Schroeder Michael A. , Fifer Robert A. 
Published: May 2005

AbstractPyrolysis‐atmospheric pressure chemical ionization was used to study the thermal decomposition of the energetic material cyclotrimethylenetrinitramine (RDX) and characterization of the individual molecular ion products was accomplished by tandem mass spectrometry. The analysis was aided with pyrolysis mass spectra of the (15N)‐ and perdeuterated RDX isotopes, and molecular formulae were derived for the m/z 46, 60, 74, 75, 85 and 98 molecular ions in the RDX pyrolysis mass spectrum. Equivalent fragments between the daughter ion mass spectra of the unlabeled and labeled RDX were determined in order to define a structure for each pyrolysis feature. Daughter ion mass spectra of pure reference compounds confirmed the identity of five of the six molecular ions. Perdeuterated RDX analyses provided evidence that m/z 74 and 75 are N,N‐dimethylformamide and N‐nitrosodimethylamine, respectively; m/z 46, 60 and 85 were identified as the protonated forms of formamide, N‐methylformamide and dimethylaminoacetonitrile, respectively.
Ion chemistry of α‐diazoketones. 2. Synthesis of Ionized or protonated N‐tosylpyrrolidin‐3‐ones from 1‐diazo‐4‐tosylaminobutan‐2‐ones under electron impact or chemical ionization
Authors: Selva Antonio , Saba Antonio 
Published: May 2005

AbstractMass spectral syntheses of gaseous ionized or protonated N‐tosylpyrrolidin‐3‐ones from 1‐diazo‐4‐tosylaminobutan‐2‐one substrates under electron impact or protonating chemical ionization conditions, respectively, are supported by collisional activation experiments.
Photodissociation and structures of [C6H4]+ ˙ ions generated from cyanobenzene and other precursors
Authors: van Der Hart W. J. , Oosterveld E. , Molenaar‐Langeveld T. A. , Nibbering N. M. M. 
Published: May 2005

AbstractPrevious work on the electron impact induced loss of hydrogen cyanide from the radical cations of cyanobenzene has revealed that ring opening is important in the formation of the corresponding [C6H4]+ ˙ ions. Photodissociation experiments now show that these [C6H4]+ ˙ ions and those generated from 2‐ethynylpyridine, 1,3‐hexadiyn‐6‐nitrile and 1,2‐diiodobenzene all photodissociate in the visible region to [C4H2]+ ˙. The corresponding photodissociation spectra are all the same and have a maximum at about 370 nm, in agreement with spectra of ions with three conjugated double or triple bonds. Owing to the high reactivity, the low photodissociation rate and, possibly, the internal energy of the ions, the photodissociation kinetics are too complicated to be solved. The experiments nevertheless show that at least a major fraction of the [C6H4]+ ˙ ions has a ring‐opened structure. This conclusion is supported by MNDO calculations, which indicate that the heats of formation of the possible acyclic structures are about 150 kJ mol−1 lower than those of the o‐, m‐ and p‐benzyne structures.
Sequence‐specific fragmentation of benzyloxycarbonyl dipeptides by resonance‐enhanced multiphoton ionization
Authors: Segar Kimberly R. , Johnston Murray V. 
Published: May 2005

AbstractThe mechanism of fragment ion formation in resonance‐enhanced multiphoton ionization (REMPI) of benzyloxycarbonyl (CBZ)‐derivitized dipeptides is presented. At 266 nm, the entire multiphoton process can be thought of as a two‐part scheme where ionization occurs by resonant two‐photon ionization followed by photodissociation of the created ions. When the energy of two photons exceeds the molecular ionization energy by a significant amount, REMPI has the advantage of producing both parent ions and low appearance energy fragments in large amounts. For CBZ dipeptides, resonant two‐photon ionization at 266 nm produces parent ions as well as A type sequence ions with high abundance. On the other hand, a three‐photon process (resonant two‐photon ionization followed by parent ion photodissociation) forms sequence‐related ions which also involve complex fragmentations of the CBZ chromophore. These results are compared to mass spectra obtained by other ionization/dissociation methods and to REMPI mass spectra of related compounds. Factors related to molecular structure elucidation based upon REMPI mass spectra are discussed. Enhanced isomer distinction is demonstrated for CBZ‐leu‐ala‐OCH3 and CBZ‐ile‐ala‐OCH3 based upon REMPI fragmentation.
The distonic ion ˙CH2CH2CO+ and its formation from ionized cyclopentanone
Authors: Traeger John C. , Hudson Charles E. , McAdoo David J. 
Published: May 2005

AbstractCollisional activation decomposition (CAD) spectra are interpreted as indicating that formation of ˙CH2CH2CO+ (1) from ionized cyclopentanone, succinic anhydride arid butyrolactone is important at 70 eV electron energy. However, photoionization appearance energy measurements and CAD spectra demonstrate that CH3CHCO+· (3) is formed from ionized cyclopentanone near threshold. Ab initio molecular orbital calculations place ΔH f (1) about 36 kJ mol−1 above ΔH f (3).
Comparative chemical ionization mass spectra of tricyclic antidepressant amines and related compounds
Authors: Schildcrout Steven M. , Geidner Robert M. 
Published: May 2005

AbstractPositive‐ion methane chemical ionization (CI) mass spectra were obtained for seven underivatized tricyclic amines: amitriptyline, nortriptyline, protriptyline, imipramine, desipramine, cyclobenzaprine and cyproheptadine. Some discrepancies in previously reported spectra were noted. Spectra of protriptyline, cyclobenzaprine and cyproheptadine are reported for the first time. Comparisons are made among the CI spectra and with electron ionization spectra, and relative abundances of major CI ions among the seven compounds are rationalized in terms of substituent and geometric effects.In most cases low‐mass iminium ions from anion abstraction were more abundant than [MH]+. Hydride abstraction and adduct formation with reagent‐gas ions were important. The three heterocyclic amines gave abundant [M]+˙ by electron transfer. Protonation at the nitrogen atom on the side chain followed by amine elimination gave tricyclic aromatic fragment ions.
Reactions of the trimethylsilyl ion with 1,2‐cyclopentanediol isomers in the collision region of a triple quadrupole instrument
Authors: Meyerhoffer William J. , Bursey Maurice M. 
Published: May 2005

AbstractIon‐molecule reactions with the trimethylsilyl ion were used to distinguish between cis‐ and trans‐1,2‐cyclopentanediol isomers. The ion kinetic energy of [Si(CH3)3]+ was varied from 0 eV to 15 eV (center of mass frame of reference). At low ion kinetic energies (<4 eV), there are significant differences in the relative stabilities and decomposition behavior of the adduct ions [M + Si(CH3)3]+. The cis‐1,2‐cyclopentanediol isomer favors decomposition of [M + Si(CH3)3]+ to yield the hydrated trimethylsilyl ion [Si(CH3)3OH2]+ at m/z 91. For the trans isomer, the formation of the hydrated trimethylsilyl ion is an endothermic process with a definite threshold ion kinetic energy.
N‐phosphoryl amino acids and peptides. Part II: Fast atom bombardment mass spectrometry of N‐di‐isopropyloxyphosphoryl and N‐dibutyloxyphosphoryl amino acids
Authors: Xue Chu‐Biao , Yin Ying‐Wu , Yu Xiao , Zhao Yu‐Fen 
Published: May 2005

AbstractThe positive ion fast atom bombardment mass spectra of N‐di‐isopropyloxyphosphoryl (Dipp) and N‐dibutyloxyphosphoryl (Dbp) amino acids or amino acid methyl esters are presented; and according to the observation of the metastable ions and the high‐resolution accurate mass measurement their fragmentation patterns are postulated. Both types of compounds were found to undergo similar fragmentations to produce (HO)2P(O)NCHR + H+, in most cases as the most abundant fragment ion of structural significance. An intrinsical difference between the two types of compounds is that N‐Dippamino acids appear to favour the successive losses of two molecules of propylene, while the loss of HCOOH seems to be preferred by the Dbp amino acids. For those compounds containing an extra functional group on the side chain of amino acids such as serine or glutamic acid some other type of fragmentation was observed besides the normal phenomenon.
Positive desorption chemical ionization/tandem mass spectrometry of natural isomeric morphinans: Regioselectivity of protonation, positional and stereochemical effects upon decomposition
Authors: Charles Brigitte , Cole Richard B. , Bruneton Jean , Tabet Jean‐Claude 
Published: May 2005

AbstractFragmentations of naturally occurring morphinan isomers have been studied using a triple quadrupole mass spectrometer. Protonated molecules were generated via desorption chemical ionization using ammonia and methane as reagent gases. Mechanistic analysis of conformationally specific and stereospecific decomposition pathways has been performed and corroborated using deuterium labelling. Strong evidence of regioselective protonation has been offered, suggesting significant differences in the distribution of protonation sites as a function of reagent gas proton affinity.
On the stereospecificity of the structurally diagnostic m/z 84 ion in the mass spectra of gibberellins and kaurenes with a 15‐hydroxy substituent
Authors: Macleod John K. , Monahan Lilian C. 
Published: May 2005

AbstractThe presence of a 15‐hydroxy substituent in naturally‐occurring kaurenes and gibberellins gives rise to a structurally diagnostic ion at m/z84 (C5H8O) in their electron‐impact mass spectra, which shifts to m/z156 for the TMS derivative, and is unaffected by differences in the A and B rings. Studies on a model tricyclic system have shown that this ion is more intense when the stereochemistry of the B/C ring junction is cis than when it is trans. In accordance with a previously proposed pathway for the formation of this ion, deuterium labelling confirms that there is a site‐specific transfer of the β‐hydrogen from the cis ring junction to the C5 fragment ion, although a minor modification of the earlier mechanism is proposed.
The [CH5NO]+ ˙ potential energy surface: Distonic ions, lon‐dipole complexes and hydrogen‐bridged radical cations
Authors: Burgers Peter C. , Lifshitz Chava , Ruttink Paul J. A. , Schaftenaar Gijs , Terlouw Johan K. 
Published: May 2005

AbstractBy combining results from a variety of mass spectrometric techniques (metastable ion, collisional activation, collision‐induced dissociative ionization, neutralization‐reionization spectrometry, 2H, 13C and 18O isotopic labelling and appearance energy measurements) and high‐level ab initio molecular orbital calculations, the potential energy surface of the [CH5NO]+ ˙ system has been explored. The calculations show that at least nine stable isomers exist. These include the conventional species [CH3ONH2]+ ˙ and [HOCH2NH2]+ ˙, the distonic ions [OCH2NH3]+ ˙, [ONH2CH3]+ ˙, [CH2O(H)NH2]+ ˙, [HONH2CH2]+ ˙, and the ion‐dipole complex CH2NH2+ …︁ OH˙. Surprisingly the distonic ion [CH2ONH3]+ ˙ was found not to be a stable species but to dissociate spontaneously to CH2O + NH3+ ˙. The most stable isomer is the hydrogen‐bridged radical cation [HCO …︁ H …︁ NH3]+ ˙ which is best viewed as an immonium cation interacting with the formyl dipole. The related species [CH2O …︁ H …︁ NH2]+ ˙, in which an ammonium radical cation interacts with the formaldehyde dipole is also a very stable ion. It is generated by loss of CO from ionized methyl carbamate, H2NC(O)OCH3 and the proposed mechanism involves a 1,4‐H shift followed by intramolecular ‘dictation’ and CO extrusion. The [CH2O …︁ H …︁ NH2]+ ˙ product ions fragment exothermically, but via a barrier, to NH4+ ˙ HCO…︁ and to H3NC(H)O+ ˙ H˙. Metastable ions [CH3ONH2]+…︁ dissociate, via a large barrier, to CH2O + NH3+ + and to [CH2NH2]+ + OH˙ but not to CH2O+ ˙ + NH3. The former reaction proceeds via a 1,3‐H shift after which dissociation takes place immediately. Loss of OH˙ proceeds formally via a 1,2‐CH3 shift to produce excited [ONH2CH3]+ ˙, which rearranges to excited [HONH2CH2]+ ˙ via a 1,3‐H shift after which dissociation follows.
Collision‐induced dissociations of deprotonated peptides, dipeptides and tripeptides with hydrogen and alkyl α groups. An aid to structure determination
Authors: Eckersley Mark , Bowie John H. , Hayes Roger N. 
Published: May 2005

AbstractThe characteristic collision‐induced dissociations of [M  H]− ions of dipeptides and tripeptides involve proton transfer to the carboxylate centre as a prelude to fragmentation. Dipeptides show the process NH2CH(R1)CONHCH(R2)CO2− → NH2C(R1)CONHCH(R2)CO2H → −NHCH(R2)CO2H + NH2C(R1)CO (R = H or alkyl) while tripeptides show the analogous processes NH2CH(R1)CONHCH(R2)CONHCH(R3)CO2− → NH2CH(R1)CONHC(R2)CONHCH(R3)CO2− → NHCH(R3)CO2H + NH2CH(R1)CONHC(R2)CO and NH2CH(R1)CONHCH(R2)CONHCH(R3)CO2− → NH2C(R1)CONHCH(R2)CONHCH(R3)CO2H → −NHCH(R2)CONHCH(R3)CO2H + NH2C(R1)CO. These fragmentations provide ready identification of the peptide.
Identification of butyryl derivatives of cyclic nucleotides by positive ion fast atom bombardment mass spectrometry and mass‐analysed ion kinetic energy spectrometry
Authors: Newton Russell P. , Walton Terence J. , Basaif Salem A. , Jenkins Andrea M. , Brenton A. Gareth , Ghosh Dipankar , Harris Frank M. 
Published: May 2005

AbstractThe syntheses of the dibutyryl derivatives of the 3′,5′‐cyclic monophosphates of adenosine, guanosine and cytidine are described. The fast atom bombardment mass spectra of these compounds are discussed, together with the mass‐analysed ion kinetic energy spectra of their protonated molecular ions and of diagnostic fragments. A protocol for the identification of the derivatives is reported which includes criteria for confirming retention of the cyclic phosphodiester moiety, substitution of both heterocyclic base and ribose ring, and butyrylation of the 2′‐O‐position. The origins of significant fragments in the spectra are discussed.