Mass-analysed Ion Kinetic Energy Spectra Research Articles

What a difference a chlorine makes: The remarkable unimolecular ion chemistry of phenyl formate and phenyl chloroformate.

Imaging photoelectron photoion coincidence (iPEPICO) spectroscopy and tandem mass spectrometry were employed to explore the ionisation and dissociative ionisation of phenyl formate (PF) and phenyl chloroformate (PCF). The threshold photoelectron spectra of both compounds are featureless and lack a definitive origin transition, owing to the internal rotation of the formate functional group relative to the benzene ring, active upon ionisation. CBS-QB3 calculations yield ionisation energies of 8.88 and 9.03 eV for PF and PCF, respectively. Ionised PF dissociates by the loss of CO via a transition state composed of a phenoxy cation and HCO moieties. The dissociation of PCF ions involves the competing losses of CO (m/z 128/130), Cl (m/z 121) and CO2 (m/z 112/114), with Cl loss also shown to occur from the second excited state in a non-statistical process. The primary CO- and Cl-loss fragment ions undergo sequential reactions leading to fragment ions at m/z 98 and 77. The mass-analysed ion kinetic energy (MIKE) spectrum of PCF+ showed that the loss of CO2 occurs with a large reverse energy barrier, which is consistent with the computationally derived minimum energy reaction pathway.

2-Benzylindane radical cations in the gas phase (Part I): Substituent effects on a stereoselective McLafferty reaction and related hydrogen transfer processes

In the present and the accompanying article, the unimolecular fragmentation of the radical cations of 2-benzylindane and eleven derivatives bearing meta- or para-substituents at the benzylic moiety has been studied with a special focus on the hydrogen exchange that precedes the McLafferty reaction. Standard EI mass spectra, low-energy (11eV) mass spectra and mass-analyzed ion kinetic energy (MIKE) spectra were recorded to probe the excitation-energy and ion-lifetime dependence of the fragmentation and the hydrogen exchange. Density-functional theory calculations were used to rationalize the substituent effects on the competition between the benzylic cleavage and the McLafferty reaction and to clarify the role of the distonic arenium ion-type intermediate formed by the γ-hydrogen-transfer step of the McLafferty reaction. The ipso-protonolysis of the benzyl residue giving rise to the loss of substituted benzenes specifically from most of the para-isomers was also found to reflect the hydrogen exchange.

Unidirectional triple hydrogen rearrangement in the radical cations of electron-rich 3-aryl-1-propanols: further evidence and limitation.

The unidirectional triple-hydrogen (3H) rearrangement of the radical cations of 3-aryl-1-propanols bearing an electron-rich substitutent in the para-position was investigated for the diastereomeric 2-(4-dimethylamino)benzylcyclohexanols and 2-(4-dimethylamino)-benzylcyclopentanols and confirmed to be a highly stereospecific feature. Whereas the standard electron ionization (EI) (70 eV) mass spectra of the trans-isomers exhibit very minor (approximately 2%-3%) albeit stereospecific peaks for the relevant C8H13N*+ ions (m/z 123), the metastable ion [mass-analyzed ion kinetic energy (MIKE)] spectra show these peaks with significant relative intensity (8%-17%). The respective cis-isomers do not undergo the 3H rearrangement, be it under standard or under metastable-ion conditions. The stereospecific 3H rearrangement is suppressed in the radical cations of cis- and trans-3-(4-dimethylamino)phenylcyclohexanol, the mass and MIKE spectra of which are governed by cleavage processes of the cyclohexane ring, which impedes the stereochemical assignment of the isomers by mass spectrometry. A multistep mechanism for the unidirectional 3H rearrangement is discussed in view of the present and previous experimental data.

Unimolecular reactions of gaseous picoline radical cations. A new experimental and computational study

The fragmentation reactions of the molecular ion of the three isomeric methylpyridines (2-picoline 1, 3-picoline 2, and 4-picoline 3) were studied using methods of tandem mass spectrometry and quantum chemical calculations with Gaussian-3 (G3) theory using the B3LYP density functional method (G3//B3LYP). Additionally RRKM calculations of the microcanonical rate constants of selected reaction pathways were performed. Derivatives of 2- and 4-picoline which bear an isotopically labeled methyl substituent (CD3: 1-d3 and 3-d3, 13CH3: 1-13C and 3-13C) were also analyzed. Of the four primary dissociation reactions of the picoline radical cations 1+–3+, the loss of a hydrogen atom, the elimination of an ethyne molecule and the elimination of a hydrogen cyanide molecule are observed in the MIKE spectra, while the loss of a methyl radical is only found in the collisional activation (CA) mass spectra of the molecular ions. The CA mass spectra of the labeled picoline radical ions reveal that some positional hydrogen exchange and carbon exchange takes place before the loss of the methyl radical. According to the G3 and RRKM calculations, the direct cleavage of the methyl substituent competes effectively with increasing internal energy of the ion with the loss of a methyl radical after rearrangements. The other three pathways found for metastable molecular ions are accompanied by efficient or complete hydrogen scrambling. The theoretical calculations prove that this scrambling occurs mainly by initial H-transfer from the methyl group to the pyridine ring and a subsequent H-ring walk. The calculations show further, that loss of H may occur from many of the intermediate ions after the rearrangements but that the direct loss of H from the methyl substituent competes successfully even at low energies, contrary to the behavior of the toluene radical ion. The elimination of an ethyne molecule gives rise to a broad flat-topped signal in the mass-analyzed ion kinetic energy (MIKE) spectra, and the MIKE spectra of 1-13C and 3-13C exhibit a 1:1 sharing of the 13C-label between ionic and neutral products. These particular features are explained by the theoretical calculations by a first rearrangement of the picoline radical cations to a seven-membered aza-cycloheptatriene radical cation 4+ followed by a rearrangement to a more rigid bicyclo-[3.2.0] isomer before the elimination of ethyne. Finally, the elimination of a hydrogen cyanide molecule exhibits only minor loss of 13C-label in the case of 1-13C and 3-13C. This observation does not agree with any mechanism including a rearrangement to 4+. The theoretical calculations suggest that instead the loss of the hydrogen cyanide molecule proceeds by a cleavage of the pyridine ring after the initial H-transfer from the methyl substituent. Although this pathway needs more energy than a rearrangement to 4+, its rate coefficients are superior owing to its loose transition states.

Ni+reactions with aminoacetonitrile, a potential prebiological precursor of glycine

The gas-phase reactions between Ni(+) ((2)D(5/2)) and aminoacetonitrile, a molecule of prebiological interest as possible precursor of glycine, have been investigated by means of mass spectrometry techniques. The mass-analyzed ion kinetic energy (MIKE) spectrum reveals that the adduct ions [NC--CH(2)--NH(2), Ni(+)] spontaneously decompose by loosing HCN, H(2), and H(2)CNH, the loss of hydrogen cyanide being clearly dominant. The structures and bonding characteristics of the aminoacetonitrile-Ni(+) complexes as well as the different stationary points of the corresponding potential energy surface (PES) have been theoretically studied by density functional theory (DFT) calculations carried out at B3LYP/6-311G(d,p) level. A cyclic intermediate, in which Ni(+) is bisligated to the cyano and the amino group, plays an important role in the unimolecular reactivity of these ions, because it is the precursor for the observed losses of HCN and H(2)CNH. In all mechanisms associated with the loss of H(2), the metal acts as hydrogen carrier favoring the formation of the H(2) molecule. The estimated bond dissociation energy of aminoacetonitrile-Ni(+) complexes (291 kJ mol(-1)) is larger than those measured for other nitrogen bases such as pyridine or pyrimidine and only slightly smaller than that of adenine.

Benzyl ions from 1,1‐(2,2′‐dimethoxyphenyl)‐substituted 2‐methylpropanes under electron ionization

The electron ionization (EI)-induced fragmentations of a series of 1,1-(2,2'-dimethoxyphenyl)-substituted 2-methylpropanes (1-20) in both 70 eV and mass-analyzed ion kinetic energy (MIKE) spectra have been investigated. The EI-MS spectra of these compounds are characterized by the presence of abundant benzyl ions. These ions result from competitive hydrogen migration from the 2- and 2'-methoxy groups on the carbenium center of the diphenylmethyl cations formed by benzylic cleavage of the molecular ions. The relative abundances of the benzyl ions arising from such competitive processes are discussed and rationalized. The steric effect of the 3- or 3'-substituents is the main discriminating factor between the two competitive processes. The structural information, arising either from the 70 eV or the MIKE spectra, is discussed.

Study of Hexanitrohexaazaisowurtzitane Ion Dissociation Mechanisms Based on Mass-Analyzed Ion Kinetic Energy Spectrum

The ion dissociation pathways of hexanitrohexaazaisowurtzitane (HNIW) are studied in this paper. A mass spectrometer with mass-analyzed ion kinetic energy spectrum is used for studying ions produced by electron impacts onHNIW. Dissociation processes from various precursor ions to product ions are proposed. Fifteen fragments including the largest m/z 392 and the smallest m/z 67 and m/z 54 are discussed. Dissociation of HNIW precursor ions with NO 2 was found to produce product ions with removal of NO 2 or NO molecules through β-inducement or α-inducement effects. HNIW framework precursor ions produce ions at (m-27)/z through losing HCN and ions at (m-1)/z through losing H atoms. Possible structures of HNIW-NO 2 ions and framework ions are suggested.

Unimolecular Dissociations of C70+ and Its Noble Gas Endohedral Cations Ne@C70+ and Ar@C70+: Cage-Binding Energies for C2 Loss

The energetics and dynamics of unimolecular decompositions of C70+ and its noble gas endohedral cations, Ne@C70+ and Ar@C70+, have been studied using tandem mass spectrometry techniques. The high-resolution mass-analyzed ion kinetic energy (HR-MIKE) spectra for the unimolecular reactions of C70+, Ne@CC70+, and Ar@C70+ were recorded by scanning the electrostatic analyzer and using single-ion counting that was achieved by combination of an electron multiplier, amplifier/discriminator, and multichannel analyzer. These cations dissociate unimolecularly via loss of a C2 unit, and no endohedral atom is observed as fragment. The activation energies for C2 evaporation from Ne@C70+ and Ar@C70+ are lower than those for elimination of the endohedral noble gas atoms. The kinetic energy release distributions (KERDs) for the C2 evaporation have been measured and, by use of the finite heat bath theory (FHBT), the binding energies for the C2 emission have been deduced from the KERDs. The C2 evaporation energies increase in the order DeltaEvap(C70+) < DeltaEvap(Ne@C70+) < DeltaEvap(Ar@C70+), but no big difference in the cage binding was observed for C70+, Ne@C70+, and Ar@C70+, indicating incorporations of the Ne and Ar atoms into C70 contribute a little to the stability of C70 toward C2 loss, which is in good agreement with theoretical calculations but contrasts with the findings in their C60 analogues and in metallofullerenes that the decay energies of the filled fullerenes are much higher than those of the corresponding empty cages.

Unimolecuclar Fragmentation and Isomerization of Gaseous Arsanyl Cations Y—C6H4As+X (X=F, Cl, Br, I). The Role of Non-Classical Nido Structures

The halogeno-(4-halogenophenyl)arsanyl cations Y–C6H4As+X (X=F, Cl, Br, I) are abundant in the 70 eV EI mass spectra of dihalogeno-(4-halogenophenyl)arsanes Y–C6H4AsX2. This has been used to study the unimolecular reactions of ions Y–C6H4As+X by techniques of tandem mass spectrometry with respect to a possible rearrangement to nido-isomers, ñ4-(XYC6H4)As+, in which the As+ is capping a dihalogenobenzene moiety, YC6H4AX. The mass analyzed ion kinetic energy (MIKE) spectra of Y–C6H4As+X, 1a+–3a+ and 5a+ (X, Y=F, Cl, Br, see Scheme 2), display broad and even dish-topped peaks for the loss of HX and HY, respectively, indicating a large kinetic energy release ( KER) during these reactions and the presence of a large reverse activation energy. The mean value of the KER, &lt; T&gt;, is specific for the type of the halogen substituent but independent of its original position and is identical to &lt; T&gt; found for the loss of HX or HY from metastable halogeno–phenylarsanyl cations, C6H5As−X or C6H4As+Y. These results give strong evidence for a positional change of X and Y in Y–C6H4As+X before fragmentation, plausibly via intermediate ñ4-(XYC6H4)As+. However, the relative intensities of the signals for loss of HX and HY are different in the MIKE spectra of isomeric arsanyl cations and the spectra of the isomers obtained by collision-induced decomposition show that the metastable arsanyl cations represent a mixture of isomers with the original arsanyl cation prevailing. Clearly, interchange of halogen substituents in Y–C6H4XAs+ is slow compared with fragmentation and the intermediate nido-isomer, ñ4-(XYC6H4)As+, is separated from the isomers of the classical structure of a halogeno-(halogenophenyl)arsanyl cation by substantial activation barriers. Therefore, in the case of 4a+ and 6a+ (X, Y=Cl, I), any rearrangement is obstructed by the facile loss of the weakly bonded I substituent. This reaction model was verified by theoretical calculations of relevant stationary points of the minimum energy reaction pathways ( MERP) of fragmentation and rearrangement at the level UBHLYP/6-311+g(2d,p)//UBHLYP/6-31+g(d). In particular, the calculations show that the nido isomers, ñ4-(XYC6H4)As+, are stable species but higher in energy than their “classical” isomers.

Electron ionization mass spectrometry as a tool for the investigation of the ortho effect in fragmentation of some Schiff bases derived from amphetamine analogs

The electron ionization-induced fragmentation patterns of three forensically relevant Schiff bases, originating from the condensation between 2-, 3- and 4-methoxyamphetamine and the corresponding ketones, were studied. The proposed fragmentation routes and ion structures are supported by high-resolution data and B/E linked-scan and mass-analyzed ion kinetic energy spectra. The rationalization of the ortho effect, which is responsible for the formation of the [M-OCH3] fragment in the case of the imine bearing ortho-substituted methoxy group, is given.

The anomalous shape of the cross section for the formation of SF3+ fragment ions produced by electron impact on SF6 revisited.

The partial ionization cross section for the formation of SF(3) (+) fragment ions following electron impact on SF(6) is known to have a pronounced structure in the cross section curve slightly above 40 eV. We used the mass-analyzed ion kinetic energy (MIKE) scan technique to demonstrate the presence of a channel contributing to the SF(3) (+) partial ionization cross section that we attribute to the Coulomb explosion of doubly charged metastable SF(4) (2+) ions into two singly charged ions SF(3) (+) and F(+), with a threshold energy of about 45.5 eV. Thus the observed unusual shape of the SF(3) (+) partial ionization cross section is the result of two contributions, (i) the direct formation of SF(3) (+) fragment ions via dissociative ionization of SF(6) with a threshold energy of 22 eV and (ii) the Coulomb explosion of metastable SF(4) (2+) ions with a threshold energy of about 45.5 eV. A detailed analysis of the MIKE spectrum reveals an average kinetic energy release of about 5 eV in the Coulomb explosion of the SF(4) (2+) ions with evidence of a second channel corresponding to an average kinetic energy release of about 1.1 eV.

Kinetic energy release of protonated methanol clusters using the low-temperature fast-atom bombardment: experiment and theory combined.

Low-temperature fast-atom bombardment was found to be an excellent method for generating large protonated methanol clusters, (CH(3)OH)(n)H(+) (n = 2 to 15). Metastable dissociations of these clusters, involving elimination of one methanol molecule, were studied using mass-analyzed ion kinetic energy spectra (MIKES). From metastable peak profiles kinetic energy release (KER) distributions were obtained, even for clusters as large as (CH(3)OH)(15)H(+). The results were analyzed by a simple thermal model, by the finite heat bath theory (FHBT) and by the RRKM-based MassKinetics algorithm. The KER distribution was shown to correspond to a three-dimensional translational energy distribution, implying statistical energy partitioning in the transition state. The mean KER values and transition state temperatures were found to increase with cluster size, reaching 25 meV and approximately 210 K for large clusters (n = 10).

Investigation of 4-(nitrophenylamino)pent-3-en-2-ones and 4-(nitrobenzylamino)pent-3-en-2-ones by electron ionization mass spectrometry. Observation of characteristic ortho effects.

The compounds 4-(phenylamino)pent-3-en-2-ones (1-3) and 4-(benzylamino)pent-3-en-2-ones (4-6) substituted with a nitro group on the aromatic ring were studied by electron ionisation mass spectrometry (EIMS). It was deduced that the compounds 1-3 are converted into the tautomeric 4-(arylimino)pentan-2-one during the EI process. Mass spectrometric decompositions of ortho-substituted derivatives (1 and 4) were found to be different from those observed for meta- and para-isomers. The fragmentation pathways are discussed on the basis of data from linked B/E and B(2)/E scans, mass-analysed ion kinetic energy (MIKE) spectra, accurate mass measurements and isotope labelling.

Unimolecular Gas-Phase Reactions of Ionized Organo-Silicon Compounds. Part XVI. (CH3)3SiOCH2CH3 and (CH3)3SiOCH2CF3

The unimolecular metastable decompositions of ethoxytrimethylsilane ((CH3)3SiOCH2CH3; 1, MW: 118) and its fluorine analogue, 2,2,2-trifluoroethoxytrimethylsilane ((CH3)3SiOCH2CF3, 2; MW: 172) induced by electron ionization, have been investigated by use of mass-analyzed ion kinetic energy (MIKE) spectrometry and D-labeling. Both molecular ions are formed in low abundance. The fragmentation of 1+ · is different from that of 2+ · , except for the loss of CH3 from the corresponding molecular ions. The MIKE spectra of the [M - CH3]+ ions from 1+ · and 2+ · gave five and three fragment ions, respectively. Two of the five reactions for 1 leading to the formation of the ion at m/z 101, (CH3)2Si+OCH = CH2, and m/z 61, CH3Si+HOH, concern new mechanistic pathways, which were not described in previous reports. Skeletal rearrangement by among others F and CF3 migrations, occurs during the fragmentation of the [M - CH3]+ ions from 2+ · . The m/z 61 ions from 2+ · are both CH2OCF+ (or CH2FCO+ etc.) and CH3Si+HOH.

Reactions between Glycolic Acid and Cu+in the Gas Phase. An Experimental and Theoretical Study

The gas-phase reactions between glycolic acid and Cu+ have been investigated by means of mass spectrometry techniques. The mass-analyzed ion kinetic energy (MIKE) spectrum reveals that the adduct ions [HOCH2COOH−Cu+] decompose spontaneously by losing CH2O2, CO, and H2O. A minor fragmentation corresponding to the loss of H2 is also observed. The structures and bonding characteristics of the different complexes involved in the glycolic acid−Cu+ potential energy surface (PES) have been theoretically studied by density functional theory (DFT) calculations carried out at the B3LYP/6-311+G(2df,2p)//B3LYP/6-31G* level. The attachment of Cu+ to glycolic acid gives rise to two energetically degenerated structures: a chelated form in which Cu+ interacts with the carbonyl oxygen and the hydroxyl oxygen atoms and another one in which the attachment of Cu+ takes place exclusively at the carbonyl oxygen atom. The estimated glycolic acid−Cu+ binding energy is 222 kJ/mol. Different mechanisms for the spontaneous fragmentations observed experimentally are proposed. The main conclusion is that the loss of 46 u should correspond dominantly to the loss of formic acid and in a lower proportion to the loss of CO + H2O.

Some new diatomic molecule containing endohedral fullerenes

Several new diatomic molecule-containing endohedral fullerenes were prepared by heating C60 or C70 under high pressures of the corresponding gases. The species prepared are N2@C60, N2@C70, 13CO@C60, and 3He22Ne@C70. Their existence was demonstrated through high sensitivity, wide dynamic range mass spectrometry. Out of two thousand C60 molecules about one is observed to incorporate N2. The nitrogen molecule containing endohedral molecules are stable and the mass spectrometric signal is not lost even after several hours heating at 500 K. The corresponding endohedral ions undergo the Rice shrink-wrap mechanism; a mass-analyzed ion kinetic energy spectrum demonstrates the loss of a C2 unit from the cage. The observation of 13CO@C60 by mass spectrometry opens up the possibility for future NMR studies of this molecule. The observation of 3He22Ne@C70 is in accordance with the “promoter” mechanism of Thiel and co-worker [J. Am. Chem. Soc. 118 (1996) 7164; Helv. Chim. Acta 80 (1997) 495], whereby the singly and doubly occupied fullerenes are in equilibrium but the empty and filled fullerenes are not.

Trends in the Unimolecular Reactions of Triaryl Pnictogen Radical Cations Ar3E•+ (E = N, P, As, Sb, Bi): Reductive Elimination versus E−C Bond Cleavage

The unimolecular reactions of the molecular ions M•+ of the triphenyl pnictogens (C6H5)3E (1, E = N; 2, E = P; 3, E = As; 4, E = Sb; 5, E = Bi) have been investigated using mass-analyzed ion kinetic energy (MIKE) spectrometry to select ions of low internal excess energy. Molecular ions of triphenylamine 1 both of high and low internal energy prefer fragmentation by losses of one and two H atoms, which proceeds by a well-known reaction between two phenyl ligands resulting in fragment ions of an azafluorene structure. In contrast, the molecular ions of the heavier triphenyl pnictogens 3, 4, and 5 dissociate at high and low internal energies almost completely by generating ions C6H5E•+ (B•+; E = As, Sb, Bi). Ionized triphenyl phosphane 2 is intermediate, showing loss of H as the main reaction at low internal energy. The ions B•+ (E = As, Sb, Bi) are generated from molecular ions of low internal energy in a one-step process without ions (C6H5)2E+ (A+; E = As, Sb, Bi) being intermediates. The formation of B•+ by successive cleavages of the relatively weak E−Caryl bonds and sequential losses of two phenyl radicals, which is discussed in the literature, is definitely excluded. Direct formation of B•+ from M•+ entails reductive elimination of C6H5E•+ under ligand coupling to yield biphenyl as the neutral product. Biaryl ions have been detected earlier in 70 eV mass spectra of triaryl pnictogens, and in the case of tris(4-ethylphenyl)arsane 6 and 4-methylphenylbisphenylarsane 7, the formation of biaryl-derived ions is the main reaction in the MIKE spectra of the molecular ions, giving positive evidence for the reductive elimination process. Formation of B•+ at low and high excess energies with exclusion of the formation of intermediate A+ requires a fast and effortless rearrangement of the molecular ions into the structure of a complex which is well prepared for biaryl loss. It is assumed that this complex contains the biphenyl moiety and the fragment C6H5E rather loosely bound to one of the benzene rings. The fast isomerization of the heavier triaryl pnictogen radical cations explains also the puzzling phenomenon known for a long time that in the case of 3, 4, and 5 the appearance energy AE of ions B•+, generated by loss of two aryl radicals, is distinctly below the AE of ions A+, generated by loss of only one aryl radical.

Metastable ion study of organosilicon compounds. Part XIII: dimethoxydimethylsilane, (CH(3))(2)Si(OCH(3))(2), and dimethoxymethylsilane, CH(3)SiH(OCH(3))(2).

Unimolecular metastable fragmentations of dimethoxydimethylsilane, (CH(3))(2)Si(OCH(3))(2) (MW 120, 1), and dimethoxymethylsilane, CH(3)SiH(OCH(3))(2) (MW 106, 2), upon electron impact ionization have been studied by means of mass-analyzed ion kinetic energy (MIKE) spectrometry and the D-labeling technique in conjunction with thermochemistry. The results have been compared with those of the corresponding carbon analogues, 2,2-dimethoxypropane, (CH(3))(2)C(OCH(3))(2) (MW 104, 3) and 1,1-dimethoxyethane, CH(3)CH(OCH(3))(2) (MW 90, 4). In analogy with the cases of 3 and 4, both molecular ions from 1 and 2 are formed at very low abundance at 70 eV, and begin to decompose by the expulsion of the substituents (H, CH(3) or OCH(3)) on the central silicon atom. These decompositions are followed by the loss of a formaldehyde molecule (CH(2)O), as commonly observed in the mass spectra of methoxysilanes. Further, an ethylene (C(2)H(4)) or a dimethyl ether (CH(3)OCH(3)) molecule loss is observed in the fragmentation of some intermediate ions generated from 1(+)* and 2(+)*, but the mechanisms are different than those in the cases of 3 and 4. Some of these fragmentations are also different than those reported previously. The relative abundance of the ions in many MIKE spectra is explained by the extension of the Stevenson-Audier rule. The reaction, which is in contrast to the rule, however, is rationalized by the energy of the transition state for the reaction, estimated by semi-empirical molecular orbital calculation. The peak at m/z 59 from 2(+)* consists only of CH(3)OSi(+) ion, whereas the peak from 1(+)* consists of two different ions, CH(3)OSi(+) and (CH(3))(2)Si(+)H. The ions CH(3)OSi(+) from 1(+)* and 2(+)* are generated by at least two and three separate routes respectively.

Studies of Unsaturated C-Aryl Glycosides by Fast-Atom Bombardment Mass Spectrometry

Fast-atom bombardment (FAB) spectra, FAB mass-analyzed ion kinetic energy (FAB MIKE) spectra and FAB MIKE spectra with collision-activated dissociation (FAB CAD-MIKE) were obtained for some unsaturated anomeric C-aryl glycosides. Although the FAB MIKE and FAB CAD-MIKE spectra of the [M + H]+ ion showed no differences, differentiation of the regioisomers and anomers was possible by analyzing the MIKE and CAD-MIKE spectra of the [M + Li]+ or [M + Na]+ ions.

Studies in organic mass spectrometry. Part 27. Electron ionisation induced isomerisation of 3‐aryl‐4(3H)‐quinazolinones†

AbstractThe comparison between 70 eV EI (electron ionisation) mass spectra, MIKE (mass analysed ion kinetic energy) and CID (collision induced dissociation) MIKE spectra, KER (kinetic energy release) and KERD (kinetic energy release distribution) data for 2‐methyl‐3‐aryl‐4(3H)‐quinazolinones 1–4, with those of the corresponding 2‐methyl‐4‐aryloxyquinazolines 1′–4′, indicates that aryloxy radical as well as hydrogen or methyl radical losses involve the formation of common intermediates. This suggests the occurrence of migrations of aryl groups from the N‐3 atom to carboxylic oxygen in the molecular ions of 1–4. Copyright © 2001 John Wiley &amp; Sons, Ltd.