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1.
The mass spectra of diethyl phenyl phosphates show substituent effects with electron-donating groups favouring the molecular ion M+˙, and the [M? C2H4]+˙, [M – 2C2H4]+˙ and [XPhOH]+˙ ions. The [PO3C2H6]+ (m/z 109) and [PO3H2]+ (m/z 81) ions are favoured by electron-withdrawing groups. Results suggest that the formation of the [XPhC2H3]+˙ ion involves rearrangement of C2H3 to the position ortho to the phosphate group. Ortho effects are also observed.  相似文献   

2.
The gas phase heats of formation of several organosulfur cations were determined from thiirane, thietane and tetrahydrothiophene precursor molecules by photoionization mass spectrometry. Heats of formation at 0 K and 298 K are reported for the following ions: [H2CS], [H3CS]+, [C2H3S]+, [C2H4S], [C3H5S]+, [C3H6S], [C4H7S]+ and [C4H8S]. The [C4H7S]+ (m/z 87), [C2H4S] (m/z 60), [C2H3S]+ (m/z 59), [C4H7]+ (m/z 55), [C4H6] (m/z 54) and [CH2S] (m/z 46) ions are produced from metastable tetrahydrothiophene ions at photon energies between 10.2 and 10.7 eV. Decay rates of internal energy selected parent ions to the m/z 60, 59, 55 and 54 fragments were measured by threshold photoelectron-photoion coincidence, the results of which are compared to statistical theory (RRKM/QET) calculations. The [C2H4S] ion from tetrahydrothiophene is found to have the thioacetaldehyde structure. From the measured [C2H4S] onset a ΔH = 50±8 kJ mol?1 was calculated for the thioacetaldehyde molecule.  相似文献   

3.
Collisional activation of the molecular ions of 1-propanol, 2-propanol and methyl ethyl ether, and of the m/z 60 ion from 1,2-dimethoxyethane provides evidence for four distinct forms of [C3H8O]. Collision induced decompositions may be explained either by simple cleavages, by cyclic processes involving adjacent substituents, or by bicyclic processes of adjacent substituents. Evidence for a form of [C3H8O] in which charge and radical site are separate is assembled from the spectra.  相似文献   

4.
For compounds C6H5X (X?Cl, Br, I) under chemical ionization conditions, methylamine causes ipso substitution of X by [NH2CH3]+ and by [NH2]+˙. C6H5F is less reactive; it gives some [C6H5NH2]+˙. Nitrobenzene gives an adduct ion [M+CH3NH3]+, a reduction product ion [C6H5NO2]+˙, and an ion at m/z93, probably a substitution product [C6H5NH2]+˙, but no [C6H5NH2CH3]+. It is also shown that the ion m/z94, formed from nitrobenzene with ammonia as reagent gas, is a substitution product rather than a reduction product ion. Carbonyl compounds C6H5. CO. X give adduct ions and some substitution, mainly [C6H5NH2]+˙.  相似文献   

5.
[C8H6O]+˙ ions with o-quinonoid ketene, benzocyclobutenone, phenyl ketene and benzofuran structures have been generated from various precursors. Their collisionally induced decompositions in both field free regions of a double focusing mass spectrometer with so-called reversed geometry have been studied using mass analysed ion kinetic energy scans and B/E linked scans. In both cases the abovementioned [C8H6O]+˙ structures can be distinguished–except the benzocyclobutenone ion which gives very similar spectra to the o-quinonoid ion–on the basis of the intensity ratios [m/z 77]/[m/z 76] and [m/z 104]/[m/z 102]. The stable [C8H6O]+˙ ions generated from the molecular ions of 7 -phenylbicyclo[3.1.1]heptan-6-one appear to have the phenyl ketene structure, as was suspected from previous kinetic energy release measurements.  相似文献   

6.
Electron impact mass spectrometry of a range of amidines (R′NC(R)NHR′) including formamidines, acetamidines, benzamidines and tert-butylamidine, has been undertaken, and comparisons made of the fragmentation pathways followed by the different families of compounds. Fragmentation of all the molecular ions is characterized by skeletal carbon-nitrogen bond cleavage to form [R′NCR]+ and [R′NH]+ fragments, both of which are observed. For formamidines (R?H), the positive charge remains with the [R′NH]+ fragment which leads to the base peak at m/z93 corresponding to [R′NH2]+˙. In contrast, for acetamidines and benzamidines the charge prefers to remain with the [R′NCR]+ fragment which gives the base peak for these compounds. The spectra of unsubstituted amidines (HNC(R)NH2) are characterized by cleavage of the carbon substituent from the NCN skeleton, [CN2H3]+ (m/z 43) being produced in all cases.  相似文献   

7.
The substituent effect on the single and double hydrogen atom transfer reactions in para-substituted benzoic acid isobutyl esters has been investigated by electron impact mass spectrometry. Electron-donating substituents favour formation of the [M? C4H8]+˙ ion generated by single hydrogen atom transfer reaction (McLafferty rearrangement), whereas electron-withdrawing substituents favour formation of the [M? C4H7]+ ion generated by double hydrogen atom transfer reaction. In the case of the latter compounds, the m/z56 ([C4H8]+˙) ion, which is generated by single hydrogen atom transfer reaction with charge migration, is very intense, while in the former compounds, the m/z56 ion is very weak. These observations can be reasonably explained on thermochemical grounds based on the sum of the standard heats of formation of the fragments.  相似文献   

8.
The [C4H6O] ion of structure [CH2?CHCH?CHOH] (a) is generated by loss of C4H8 from ionized 6,6-dimethyl-2-cyclohexen-1-ol. The heat of formation ΔHf of [CH2?CHCH?CHOH] was estimated to be 736 kJ mol?1. The isomeric ion [CH2?C(OH)CH?CH2] (b) was shown to have ΔHf, ? 761 kJ mol?1, 54 kJ mol?1 less than that of its keto analogue [CH3COCH?CH2]. Ion [CH2?C(OH)CH?CH2] may be generated by loss of C2H4 from ionized hex-1-en-3-one or by loss of C4H8 from ionized 4,4-dimethyl-2-cyclohexen-1-ol. The [C4H6O] ion generated by loss of C2H4 from ionized 2-cyclohexen-1-ol was shown to consist of a mixture of the above enol ions by comparing the metastable ion and collisional activation mass spectra of [CH2?CHCH?CHOH] and [CH2?C(OH)CH?CH2] ions with that of the above daughter ion. It is further concluded that prior to their major fragmentations by loss of CH3˙ and CO, [CH2?CHCH?CHOH]+˙ and [CH2?C(OH)CH?CH2] do not rearrange to their keto counterparts. The metastable ion and collisional activation characteristics of the isomeric allenic [C4H6O] ion [CH2?C?CHCH2OH] are also reported.  相似文献   

9.
Twelve 2,3′-bisindolylmethanes with various substituents were investigated using electrospray ionization quadrupole time-of-flight tandem mass spectrometry in positive ion mode. A retro-[3+2] reaction was observed in the collision-induced dissociation spectra of protonated 2,3′-bisindolylmethanes for the first time. The mechanism of retro-[3+2] reaction was concerted or stepwise. For the concerted pathway, carbon–carbon bonds of a protonated compound simultaneously cracked and the m/z 208 ion ([C15H10D2N]+) was observed with hydrogen–deuterium exchange labeling. The stepwise pathway goes through 1,3-hydrogen migration twice and the m/z 208 ion ([C15H10D2N]+) and m/z 207 ion ([C15H11DN]+) were detected with deuterium labeling. In the deuterium-labeled tandem mass spectrum for one compound, only the peak at m/z 208 was present at high abundance, suggesting that the concerted pathway is more likely. In addition, the substituents have no obvious trends on the ratios of the product intensity to the base intensity, further supporting the concerted pathway.  相似文献   

10.
Some diverse compounds possessing a PhC?NO unit cleave the N? O link upon electron impact to give [PhCN]+˙. Different and especially significant modes of N? O scission occur in metastable processes when the oxygen atom of the PhCNO group is exocyclic to a heterocyclic nitrogen atom. Upon electron impact, rupture of the N? O bond in PhCNO-containing molecules generally dominates over 1,3-dipolar cycloreversion, which generates the radical cation of benzonitrile oxide. Stable PhCNO-containing molecules survive competing fragmentations in the ion source to produce [M+H]+ ions of moderate relative intensity. Other ions, which are larger than [M]+ are implicated where M is PhCH?NOR. Several values of m/z for metastable ions are common to compounds which have a PhCNO moiety. These m/z values generally derive both from a parent ion with m/z?105 and from a PhC?NO moiety.  相似文献   

11.
The low-energy, low-temperature mass spectra of thirteen alkanals are reported and their predominant modes of fragmentation discussed in terms of energetics. Characteristic of this class of compounds is the very high proportion of odd-electron ions in the mass spectra, namely [M ? CMH2m], [M ? H2O] and [M ? H2O ? CmH2m].  相似文献   

12.
The minimum energy, Qmin, necessary to convert an ion m1+ to a doubly charged ion m12+ is obtained for 19 different ions from methane, ammonia, water and hydrogen sulphide by charge stripping using nitrogen collision gas. The ions studied include the [MH]+ ions formed by chemical ionization in a high pressure source. Stable m12+ ions could not be formed in the case of [NH4]+, [NH], [H2O] and [OH]+. Even in these cases the value of Qmin could be estimated by studying the fragments formed from the unstable m2+ ions. In several cases, the energy required to form m12+ ions is less than the literature value for the ionization energy of m1+. This is discussed in terms of the possibility of the presence of excited states of m1+ in the present experiments.  相似文献   

13.
Nitric 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 s?p or the electrophilic substituent constant s?p+. 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.  相似文献   

14.
The reactions of metastable decomposing methyl acetoacetate (a mixture of keto a ad enol tautomers) are reported and discussed. The unimolecular fragmentations of the tautomers are different. The metastable decomposing radical cation of the keto form displays four specific ions: [M –CO]+˙, [M – CH2O]+˙, [M – CH2CO]+˙ and m/z 43. The results derived from D-, 13C- and 18O-labelled precursors together with thermochemical data have been used to study the mechanisms. Experimental results indicate that an unexpected isomerization occurs before dissociation. It formally corresponds to oxygen atom permutation of the two carbonyl groups without participation of the carbon atoms. This remarkable process is interpreted in terms of a mechanism involving ion-molecule complexes.  相似文献   

15.
Collisional activation mass spectra confirm that tolyl ions can be produced from a variety of CH3C6H4Y compounds. High purity o-, m- and p-tolyl ions are prepared by chemical ionization of the corresponding fluorides (Y=F) as proposed by Harrison. In electron ionization of CH3C6H4Y formation of the more stable tropylium and benzyl ionic isomers usually accompanies that of the o-, m- and p-tolyl ions. Isomerization of low energy [CH3C6H4Y]+? to [Y–methylenecyclohexadiene]+? is proposed to account for most [benzyl]+ formation, while the tropylium ion appears to arise from the isomerization of tolyl ions formed with higher internal energies, [o-, m-, p-tolyl]+→ [benzyl]+→ [tropylium]+, consistent with Dewar's predictions from MINDO/3 calculations.  相似文献   

16.
The sodium adduct of disodium salts of benzene dicarboxylic acids (m/z 233), when subjected to collision‐induced dissociation (CID), undergoes a facile loss of CO2 to produce an ion of m/z 189, which retains all the three sodium atoms of the precursor. The CID spectrum of this unusual m/z 189 ion shows significant peaks at m/z 167, 63 and 85. The enigmatic m/z 167 ion, which appeared to represent a loss of a 22‐Da neutral fragment from the precursor ion is in fact a fragment produced by the interaction of the m/z 189 ion with traces of water present in the collision gas. The change of the m/z 167 peak to 168, when D2O vapor was introduced to the collision gas of a Q‐ToF instrument, proved that such an intervention of water could occur even in collision cells of tandem‐in‐space mass spectrometers. The m/z 189 ion has such high affinity for water; it forms an ion/molecule complex even during the brief residence time of ions in collision cells of triple quadrupole instruments. The complex formed in this way then eliminates elements of NaOH to produce the ion observed at m/z 167. In an ion trap, the relative intensity of the m/z 167 peak increases with longer activation time even at the lowest possible collision energy setting. Similarly, the m/z 145 ion (which represents the sodium adduct of phenelenedisodium, formed by two consecutive losses of CO2 from the m/z 233 ion of meta‐ and para‐isomers) interacts with water to produce a fragment ion at m/z 123 for the sodium adduct of phenylsodium. Other uncommon ions that originate also from water/ion interactions are observed at m/z 85 and 63 for [Na3O]+ and [Na2OH]+, respectively. Tandem mass spectrometric experiments conducted with appropriately deuterium‐labeled compounds confirmed that the proton required for the formation of the [Na2OH]+ ion originates from traces of water present in the collision gas and not from the ring protons of the aromatic moiety. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

17.
The isomeric ions [H2NC(H)O]+˙, [H2NCOH]+˙, [H3CNO]+˙ and [H2CNOH]+˙ were examined in the gas phase by mass spectrometry. Ab initio molecular orbital theory was used to calculate the relative stabilities of [H2NC(H)O]+˙, [H2NCOH]+˙, [H3NCO]+˙ and their neutral counterparts. Theory predicted [H2NC(H)O]+˙ to be the most stable ion. [H2NCOH]+˙ ions were generated via a 1,4-hydrogen transfer in [H2NC(O)OCH3]+˙, [H2NC(O)C(O)OH]+˙ and [H2NC(O)CH2CH3]+˙. Its metastable dissociation takes place via [H3NCO]+˙ with the isomerization as the rate-determining step. [H2CNOH]+˙ undergoes a rate-determining isomerization into [H3CNO]+˙ prior to metastable fragmentation. Neutralization-reionization mass spectrometry was used to identify the neutral counterparts of these [H3,C,N,O]+˙ ions as stable species in the gas phase. The ion [H3NCO]+˙ was not independently generated in these experiments; its neutral counterpart was predicted by theory to be only weakly bound.  相似文献   

18.
The mass spectra of a series of β-ketosilanes, p-Y? C6H4Me2SiCH2C(O)Me and their isomeric silyl enol ethers, p-Y? C6H4Me2SiOC(CH3)?CH2, where Y = H, Me, MeO, Cl, F and CF3, have been recorded. The fragmentation patterns for the β-ketosilanes are very similar to those of their silyl enol ether counterparts. The seven major primary fragment ions are [M? Me·]+, [M? C6H4Y·]+, [M? Me2SiO]+˙, [M? C3H4]+˙, [M? HC?CCF3]+˙, [Me2SiOH]+˙ and [C3H6O]+˙ Apparently, upon electron bombardment the β-ketosilanes must undergo rearrangement to an ion structure very similar to that of the ionized silyl enol ethers followed by unimolecular ion decompositions. Substitutions on the benzene ring show a significant effect on the formation of the ions [M? Me2SiO]+˙ and [Me2SiOH]+˙, electron donating groups favoring the former and electron withdrawing groups favoring the latter. The mass spectral fragmentation pathways were identified by observing metastable peaks, metastable ion mass spectra and ion kinetic energy spectra.  相似文献   

19.
The 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.  相似文献   

20.
The ratio of the fragment ions at m/z 122 and m/z 123 in the positive ion fast atom bombardment or secondary ion mass spectra of thiamine hydrochloride varies with sample preparation and experimental conditions. For all mass spectra that contained significant abundances of matrix (S) ions [S + H]+, the fragment at m/z 123 is the more abundant of the two ions. If [S + H]+ ions are not observed in the mass spectrum under the conditions selected, the ion at m/z 122 is more abundant. This correlation suggests that hydrogen transfer to the fragment ion occurs in the gas phase, with the composition of the ion-solvent cluster ions in the selvedge region being the key factor. The ratio of the fragment ions at m/z 123 and m/z 122 is thus an indicator of the extent of protonation in the selvedge, the region immediately above the solvent surface created by primary particle bombardment.  相似文献   

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