bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chemical ionization mass spectrometry of bifunctional compounds. The behaviour of bifunctional compounds on protonation
Authors: Nakata Hisao , Suzuki Yumi , Shibata Miyuki , Takahashi Konomi , Konishi Hideyuki , Takeda Naohito , Tatematsu Akira 
Published: May 2005

AbstractPositive‐ion chemical ionization mass spectra were measured for simple bifunctional aromatic compounds of the type p‐XCH2C6H4CH2Y, where X = NH2, NH(CH3) and N(CH3)2 and Y = OH and OCH3. For each compound, essentially only three peaks of ions, [MH]+, [ MH ‐ XH] + and [MH ‐ YH] +, appeared. The B/E con stant linked‐scan spectra showed that the stable non‐decomposing [MH]+ had the proton only on the nitrogen‐containing functional group. From these data, the relative amounts of total protonation, the ratio of N‐and O‐protonation and the fraction of fragmenting [MH]+ can be calculated. The ease of protonation (protonation susceptibility) and the reactivity (fragmentation capability) of the respective functional groups are discussed.
Evidence for ion‐neutral complex‐mediated reactions well above the threshold for dissociation of the complex
Authors: McAdoo David J. , Hudson Charles E. 
Published: May 2005

AbstractThe possibility that ion‐neutral complex‐mediated eliminations occur well above the threshold for simple dissociation of the partners in the complex was explored. This was accomplished by determining whether daughter ions of probable complex‐mediated dissociations undergo metastable decompositions. All six complex‐mediated decompositions examined formed metastable ions. Therefore, a very small fraction of ion‐neutral complex‐mediated fragmentations may occur several hundred k J mol−1 above the threshold for dissociation of the partners.
Mass spectra of some α‐substituted phenyl‐α,α′‐dimethoxyl ketones and their derivatives
Authors: Chen Guoqiang , Zhang Pang 
Published: May 2005

AbstractThe mass spectra of some α‐substituted phenyl‐α,α′‐dimethoxyl ketones (compounds 1) and their 2,4‐dinitrophenylhydrazones (compounds 2) and semicarbazones (compounds 3) have been studied. The characteristic fragments at m/z (M − 73) from compounds 1, m/z (M − 253) from compounds 2 and m/z (M − 130) from compounds 3 are abundant and proposed to be [ArCROCH3]+. Fragmentations yielding [M+ − 49] from compounds 2 are abnormal and probably involve the methoxyl and nitro groups. The intense peak at m/z 130 due to [CH3OCH2CNNHCONH2]+ from compounds 3 corresponds to α‐cleavage of the molecular ion. Some other fragments from these new compounds are interpreted in this paper.
Determination and enhancement of stereospecific decompositions via triple mass spectrometry: Formation of untypical protonated precursor molecules
Authors: Cole Richard B. , Tabet Jean‐Claude 
Published: May 2005

AbstractA tetraquadrupole mass spectrometer with consecutive surface‐induced dissociation/collisionally activated dissociation (SID/CAD) capability has been used to investigate the decompositional behaviour of bifunctional terpenes. SID and CAD yield similar daughter‐ion spectra of protonated molecules generated by ammonia chemical ionization. These collision mass spectra of MH+ contain diagnostic daughter ions which can be used to distinguish diastereomeric terpenols. Pronounced stereochemical effects underlying specific decompositions of the ammonium adduct and protonated molecule forms of the bifunctional terpenes have been attributed to the formation of protonated molecules of lower stability produced via decomposition of [M + NH4]+. Evidence supporting the existence of such unusual protonated molecules formed via collision is given in the grand‐daughter spectra of [M + NH4]+. Triple mass Spectrometry is shown to promote the Stereospecific formation and subsequent diagnostic decomposition of these singular protonated forms, thus improving the ability to differentiate the diastereomers.
A combined theoretical and experimental approach to the unimolecular loss of molecular hydrogen from protonated formaldehyde: Determination of the average internal energy of metastable [CH2OH]+ ions
Authors: Hvistendahl Georg , Uggerud Einar 
Published: May 2005

AbstractAb initio quantum chemical calculations (MP2/4–31G**) were performed for the dihydrogen elimination reaction from protonated formaldehyde. The energy difference between reactants and products and the activation energies were found to be in good agreement with the corresponding experimental quantities. Theoretical rate vs. energy curves were computed for a series of isotopic variants of the reaction using the Rice–Ramsperger–Kassel–Marcus (RRKM) method. The vibrational frequencies used in these calculations were taken from the 4–31G** geometry‐optimized transition state and reactant structures. Quantum mechanical tunnelling was introduced to explain the existence of metastable CH2OH ions, and a negative kinetic shift of about 0.1 eV was found. The intramolecular kinetic isotope effect for loss of HH/HD and DH/DD was calculated and compared with the experimental data. The result is consistent with the assumption that the average internal energy of metastable [CH2OH]+ ions is very close to the critical energy for H2 loss.
Mass spectra of liquid crystals. III—phenylpyrimidine derivatives
Authors: Leclercq P. A. , van den Bogaert H. M. 
Published: May 2005

AbstractThe 70 eV electron impact mass spectra of 34 1‐phenyl‐2,5‐pyrimidine derivatives are presented. Based on the observed mass shifts by the various substituents, the nature of the main fragment ions is rationalized.
Production of metal atoms, clusters and complexes in pulsed discharge‐excited jets : Studies via mass‐resolved laser multiphoton ionization
Authors: Buntine Mark A. , McGilvery Don C. , Morrison Richard J. S. 
Published: May 2005

AbstractA pulsed, high‐voltage, discharge‐excited nozzle source has been developed and exploited to study the possibility of sputtering and entraining various metal atoms into the gas expansion from the discharge electrodes. By appropriate choice of electrode materials, atomic beams of copper, silver, tin and lead have been generated and spectroscopically characterized by 2 + 1 laser multiphoton ionization with mass analysis. Sufficiently high atomic densities are achieved with this nozzle system that metal clustering also takes place, producing dimers such as Ag2, species of mixed composition such as AgSn and trimers, Ag3. In addition, chemical reactions have been observed which can be initiated in the discharge and which lead to the formation of metal–ligand complexes when suitable molecules are seeded into the carrier gas. Mass spectral evidence for two such silver complexes is presented.
Repeller‐Induced dissociation of alkyl alcohols in thermospray mass spectrometry
Authors: Saar Jacob , Haimberg Marcela , Chenier Claude 
Published: May 2005

AbstractSix alkyl alcohols were studied using thermospray mass Spectrometry. Whereas the dominant ion in the spectrum up to a repeller potential of 120 V was [M + NH4]+, above that potential [M + H]+ and fragment ions appeared. The fragments observed were largely due to hydrogen release from alkyl ions ([CnH2n+1]+ – H2 → [CnH2n‐1]+) and loss of water or some other stable molecule from the same species. The results are compared with those from ionization of the same alcohols under electron impact and photoionization conditions and with results obtained for methanol under thermospray conditions.
Linear dependence of the intensity of the [M + H]+ ion peak in fast atom bombardment mass spectrometry on the basicity of meso‐substituted octaethylporphyrins
Authors: Van Lin , Fang Yi‐Wei , Liang Xi‐Yun , Wu Guo‐Zhang , Leung Hiu‐Kwong 
Published: May 2005

AbstractA fast atom bombardment mass spectrometric study of the meso‐substituent effect of Octaethylporphyrins (OEPX, X = NH2, CH3, H, CHO, Cl, CN, NO2) is reported. The intensity of the [M + H]+ ion peaks was estimated quantitatively using an external standard, which was observed to be correlated linearly with the basicity (pK3) of the OEPX. The pK3 value of the OEPXs was obtained by titration with perchloric acid and it was observed to be correlated linearly with Hammett's σp value, with a ρ value of 1.38.
Oligosaccharide characterizations by fast atom bombardment mass spectrometry. Fragmentation study in relation to the substituent at the reducing end
Authors: Bosso C. , Heyraud A. , Patron L. 
Published: May 2005

AbstractA systematic investigation of oligosaccharides (cello‐oligosaccharides, malto‐oligosaccharides, their corresponding alditols and methylmaltosides) was undertaken using fast atom bombardment mass spectrometry. Experimental conditions were defined in order to obtain characteristic fragmentation in relation to the structure of the oligomers. The role of substituents at the reducing end in the fragmentation process was demonstrated.
Ion‐Neutral complexes from protonated propyl phenyl ethers. Gas‐phase solvolysis versus elimination‐readdition
Authors: Kondrat Richard W. , Morton Thomas Hellman 
Published: May 2005

AbstractIon‐neutral complexes, well attested as intermediates in the expulsion of alkenes from M+⋅ and MH+ ions from primary alkyl phenyl ethers, are shown to intervene in the decomposition of the MH+ ion of a secondary alkyl phenyl ether, (CD3)2CHOPh. Chemical ionization (CI) (methane reagent gas)‐mass‐analysed ion kinetic energy spectroscopy (MIKES) shows ions of both m/z 96 and 97, indicating that the proton deposited by the CI reagent exchanges with the methyl deuterium atoms. The ratio of daughter ion intensities, as well as the proportions of ions of m/z 95, 96 and 97 from the MH+ of CD3CH2CD2OPh, agree with predictions based on the gas‐phase solvolysis mechanism, in which [i‐Pr+ PhOH] complexes form from the protonated parent via simple bond heterolysis. An alternative mechanism, elimination‐readdition, would proceed via [propene PhOHD+] complexes. This latter mechanism predicts a ratio of daughter ion intensities that is very different from gas‐phase solvolysis and which disagrees with experiment. The elimination‐readdition pathway is effectively ruled out, while the gas‐phase solvolysis mechanism is reinforced.
Gas‐Phase ring‐chain tautomerism in 1,3‐oxazines. Does it exist?
Authors: Vainiotalo Pirjo , Fülöp Ferenc , Pihlaja Kalevi 
Published: May 2005

AbstractGas‐phase ring‐chain tautomeric equilibria with eight 2‐phenyl‐substituted perhydro‐1,3‐oxazines and six 2‐aryl‐substituted l,2‐dihydro‐4H‐3,1‐benzoxazines were studied by recording their mass spectra Finder different conditions. Their fragmentation behaviour was also studied using metastable ion analysis and exact mass measurement. For the monocyclic compounds the existence of tautomerism was apparent and it resembled that found in non‐polar solvents. In contrast, benzoxazines gave little evidence for the presence of the open‐chain forms.
Factors affecting immonium ion intensities in the high‐energy collision‐induced decomposition spectra of peptides
Authors: Madden T. , Welham K. J. , Baldwin M. A. 
Published: May 2005

AbstractEach amino acid in a peptide has a characteristic immonium ion (H2N+CHR), the presence of which in a mass spectrum can indicate the presence of that amino acid. High‐energy collision‐induced decomposition studies on small peptide ions formed by fast atom bombardment showed the relative intensities of these immonium ions to be dependent on the relative positions of the amino acids in the peptide chain: C‐terminal, N‐terminal or in‐chain. Evidence in favour of competition in the formation of immonium ions is presented.
Evaluation of nitric oxide chemical ionization mass spectra of substituted benzenes
Authors: Daishima Shigeki , Lida Yoshio , Kanda Fujihiro 
Published: May 2005

AbstractNitric oxide chemical ionization mass spectra of substituted benzenes obtained with the Townsend discharge technique were studied. There were four kinds of base peaks in the mass spectra, i.e. [M + NO]+˙, M+˙, [M − H]+ and [M − OR]+ (R = H, CH3). The formation of the specific ion [M + NO]+˙ was highly dependent on the kind of substituent, and it was produced more abundantly in the case of substitutions involving electron‐accepting groups. The measure of [M + NO]+˙ production was evaluated from the value of the ratio [M + NO]+˙/M+˙. In mono‐substitutions, it was clarified that the ratios of [M + NO]+˙/M +˙ were correlated with the Hammett substituent constant s̀p or the electrophilic substituent constant s̀p+. Monosubstitutions (C6H5R) and toluene substitutions (CH3C6H4R) could be classified into six groups in terms of base peak species, [M + NO]+˙/M+˙ ratios and substituents. In disubstitutions, the mass spectral patterns were governed by the combination of substituents. Mass spectral distinctions among ortho, meta and para isomers could be made in many cases.
Novel fragmentation of N‐diisopropyloxyphosphoryl dipeptides and tripeptides by fast atom bombardment mass spectrometry
Authors: Zhao Yu‐Fen , Zhang De‐Qing , Xue Chu‐Biao , Zeng Jia‐Ning , Ji Gai‐Jiao 
Published: May 2005

AbstractPositive ion fast atom bombardment mass spectrometry of N‐diisopropyloxyphosphoryl dipeptides and tripeptides showed a novel cleavage pattern in that only the N‐phosphoryl fragment ions gave intense peaks while the C‐terminal series of ions was suppressed. The base peak was the N‐phosphoryl imino ion responding to the N‐terminal residue. These advantages are superior to those of other types of N‐protecting groups.
Site of gas‐phase methylation of l‐phenyl‐2‐aminopropane
Authors: Zagppey Herman , Fokkens Roel H. , Ingemann Steen , Nibbering Nico M. M. , Florencio Helena 
Published: May 2005

AbstractThe regioselectivity of methyl cation transfer from (CH3)2F+, (CH3)2Cl+ and (CH3)3O+ to 1‐phenyl‐2‐aminopropane was studied by Fourier transform ion cyclotron resonance in combination with collision‐induced dissociation and neutralization‐reionization mass spectrometry of the stable [M + CH3]+ ions formed in a chemical ionization source. The (CH3)2F+ ion transfers a methyl cation to the NH2 group and the phenyl ring with almost equal probability. Predominant CH3+ transfer to the NH2 group is observed for the (CH3)2Cl+ ion whereas the (CH3)3O+ ion reacts almost exclusively at the amino group. The preference for methylation at NH2 is discussed in terms of a lower methyl cation affinity of the phenyl ring than of the amino group and the existence of an energy barrier for methylation of the phenyl moiety.
A study of some imidazo[l,5‐a]benzodiazepin‐6‐ones by electron impact mass spectrometry. characterization by tandem mass spectrometry of a distonic fragment ion
Authors: Rubino Federico Maria , Zecca Luigi , Mascaro Paolo , Hunkeler Walter 
Published: May 2005

AbstractThe mass spectra of several imidazo[l,5‐a]benzodiazepin‐6‐one derivatives of neuropharmacological significance were determined in order to establish their decomposition paths under electron impact. A novel distonic fragment ion was observed and it was possible to demonstrate by consideration of metastable ions and by tandem mass spectrometry that it undergoes isomerization to the corresponding classical structure.
Improved tuning and calibration in liquid chromatography/thermospray mass spectrometry using acetic acid cluster ions
Authors: Saar Jacob , Haimberg Marcela 
Published: May 2005

AbstractTuning and calibration of a thermospray ion source can cause rapid contamination of the source, and can have the disadvantage of introducing substances or solvents that are not used in the subsequent analytical work on the mass spectrometer. The use of aqueous 0.05 M ammonium acetate alone to produce acetic acid clusters for calibration in the mass range up to m/z 800 is reported. A low temperature of the vaporizer and the source block is used in order to maintain the clusters formed. The low temperature makes possible a very good signal‐to‐noise ratio, since the only ions formed are clusters of the general formula [(CH3COOH)m(NH3)n(H2O)pNH4]+. Owing to the use of the ammonium acetate mobile phase, no interference from other sources was observed, e.g. clusters of solvents with ammonium acetate or impurities.
Structural characterization of isomeric triazolocoumarins by high‐ and low‐energy collision spectrometry of M+˙, [M + H]+ and [M − H]− species
Authors: Evans C. , Traldi P. , Chilin A. , Pastorini G. , Rodighiero P. 
Published: May 2005

AbstractTwo monometayl‐ and four dimethyl‐triazolocoumarin isomers were characterized by their electron impact mass spectra and by low‐energy collision experiments performed on molecular ions M+˙ and other fragment ions with an ion‐trap mass spectrometer. High‐energy collision‐activated dissociation measurements were performed on the protonated [M + H]+ and deprotonated [M − H]− molecular ion obtained by fast atom bombardment and M+˙ species produced by electron impact ionization on a double‐focusing, reverse‐geometry instrument. The data obtained allowed unequivocal structural identification of all the compounds investigated.
Mass spectra of some 2‐(p‐R2‐phenyl)‐indole‐3‐carboxaldehyde derivatives
Authors: Cortés C. Eduardo , Martinez Roberto , Gomez Martha B. Gutierrez 
Published: May 2005

AbstractThe mass spectra of eight new substituted 2‐(p‐R2‐phenyl)‐indole‐3‐carboxyaldehydes which have potentially useful pharmacological properties, are presented.
A McLafferty rearrangement in an even‐electron system: C3H6 elimination from the α‐cleavage product of tri‐n‐butylamine
Authors: Budzikiewicz Herbert , Bold Peter 
Published: May 2005

AbstractIt is shown by deuterium labelling, linked‐scan measurements and collision activation that the [M‐C3H7˙]+ (α‐cleavage) ion in the electron impact ionization spectrum of tributylamine loses C3H6 with transfer of one hydrogen specifically from the γ‐position. The experimental data point towards a mechanism which involves the intermediate formation of a distonic diradical ion from an excited α‐cleavage ion which then eliminates the neutral alkene.
Evidence that gas‐phase ion‐molecule reactions are responsible for the behaviour of crown ethers under fast atom bombardment conditions
Authors: Curcuruto Ornella , Traldi Pietro , Moneti Gloriano , Corda Luciana , Podda Gianni 
Published: May 2005

AbstractThe fast atom bombardment mass spectrometry of some crown ethers shows the formation of both [M + H]+ and [M − H]+ ions, paralleling behaviour already observed using electron impact ionization. The study of these oily samples with and without a glycerol matrix, trifluoroacetic acid or alkali metal salts, suggests that the ionization process does not occur in the condensed phase, but in the selvedge region by gas‐phase ion‐molecule reactions in accordance with the ‘gas‐phase explosion model’. Positive‐ion chemical ionization experiments support this proposal.
Relative intensities of metastable peaks measured with B/Elinked scan and metastable defocusing techniques
Authors: Rashkes Yakov W. , Sirotenko Elena G. , Milgrom Yurij M. 
Published: May 2005

AbstractThe ratios (A) of metas table‐ and parent‐ion peak heights measured by me testable defocusing and the B/E inked scan technique have the same order of magnitude. This was established for the M+ → [M ‐ 15]+ and M+ → [M − OR1]+ (R1 = H, Me, Ac) transitions in the mass spectra of diterpene alkaloids with a licoctonine skeleton. The A values were demonstrated to depend on the position of the eliminated group in the parent molecule. The A values can also be employed as a criterion for the identification of daughter‐ion reaction configurations.
Mass spectra of N‐arylaminosulphonylcarbethoxydiazoacetamides
Authors: Lebedev Albert T. , Bakulev Vasily A. , Kolobov Mikhail Yu. 
Published: May 2005

AbstractThe electron impact mass spectra of N‐arylaminosulphonylcarbethoxydiazoacetamides were studied. On the basis of high‐resolution mass spectrometric data, mass‐analysed ion kinetic energy Spectrometry and linked scan experiments a detailed scheme of the fragmentation is proposed. A number of possibilities of charge Iocalization are revealed in the complex decomposition processes of the molecular ions.
Thermal effects on the mass spectra of benzophenone oximes obtained by gas chromatography/electron ionization mass spectrometry
Authors: Ma Yee‐Chung , Munson Burnaby 
Published: May 2005

AbstractBenzophenone oxime and substituted benzophenone oximes can be pyroiyzed to the imines to a small extent in the heated transfer line from the gas chromatograph to the mass spectrometer source and to a large extent in the hot injection port of a gas chromatograph at high temperatures using the splitless mode of sample injection. The pyrolysis of the oximes to the imines appears to be largely a surface reaction and does not form the benzophenones as pyrolysis products. Decomposition of benzophenone oxime to benzophenone was produced by another reaction at the front of the chromatographic column. Thermal isomerizaton of benzophenone oxime to benzanilide was not observed under these conditions.
Mass spectrometry of pyrimidine derivatives: Electron impact‐induced decomposition of molecular ions of 4‐amino‐substituted and 4‐amino‐disubstituted 1,2‐dihydro‐1‐methylpyrimidin‐2‐ones
Authors: Plaziak Adam S. , Celewicz Lech , Ciszewski Krzystof , Golankiewicz Krzysztof 
Published: May 2005

AbstractElectron impact (EI) mass spectra of fourteen 4‐amino‐substiruted 1,2‐dihydro‐1‐methylpyrimidin‐2‐ones are reported. The EI‐induced decomposition of their molecular ions is significantly dependent on the chemical nature of the substituents. The routes of mass decomposition established suggest the presence of the tautomeric forms in the gas phase of some investigated compounds.
Mass spectra of picolinic, nicotinic and isonicotinic acids and of their respective N‐oxides
Authors: de Oliveira Silvana M. , de Giovani Wagner F. , Romero José Ricardo , Miller Joseph 
Published: May 2005

AbstractMass spectra of picolinic, nicotinie and isonicotinie acids and of their respective N‐oxides are presented. Picolinic acid and its N‐oxide demonstrate the facile loss of carbon dioxide and low‐intensity molecular ions. Fragmentation is relatively simple. Nicotiuic and isonicotinic acids show very similar fragmentation patterns. For both, the molecular ion is the base peak. The fragmentations of nicotinic acid N‐oxide and of isonicotinic acid N‐oxide are more complex than those of the previous four compounds, but are similar to each other.
Time‐dependence of the isotope effects in the unimolecular dissociation of tertiary amine molecular ions
Authors: Ingemann Steen , Kluft Els , Nibbering Nico M. M. , Allison Colin E. , Derrick Peter J. , Hammerum Steen 
Published: May 2005

AbstractThe intramolecular secondary isotope effects on the α‐cleavage of deuterium‐labelled N‐methyldipentylamine radical cations have been studied as a function of ion lifetime by field ionization kinetics. The isotope effects observed are all normal and increase in magnitude with increasing ion lifetime, with the exception of the δ‐labelled compound which shows an inverse effect (predominant loss of the labelled radical) at times shorter than 10−9 s, and a normal effect at longer times. The isotope effects reflect differences in zero‐point energies of the transition states as well as the influence of slight reductions of isotope‐dependent frequencies on the state sums–a statistical weight effect. The latter is particularly important at high ion energies and is the primary reason for the occurrence of the inverse isotope effect. The time dependence of the normal and inverse isotope effect is reproduced by QET/RRKM calculations.
Electron impact mass spectra of some dioximes of o‐diacyl benzenes
Authors: Kotali Antigoni 
Published: May 2005

AbstractThe electron impact mass spectra of the new synthesized dioximes of o‐diacyl benzenes (2) are reported. In addition to the molecular ion, characteristic peaks appear at values corresponding to the [M − OH] +, [M − NOH]+ and [M − NHOH]+ ions. No initial dehydration of the molecular ion has been observed.