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1.
Yassin A. Jeilani Beatriz H. Cardelino Victor M. Ibeanusi 《Journal of mass spectrometry : JMS》2010,45(6):678-685
We report the first positive chemical ionization (PCI) fragmentation mechanisms of phthalates using triple‐quadrupole mass spectrometry and ab initio computational studies using density functional theories (DFT). Methane PCI spectra showed abundant [M + H]+, together with [M + C2H5]+ and [M + C3H5]+. Fragmentation of [M + H]+, [M + C2H5]+ and [M + C3H5]+ involved characteristic ions at m/z 149, 177 and 189, assigned as protonated phthalic anhydride and an adduct of phthalic anhydride with C2H5+ and C3H5+, respectively. Fragmentation of these ions provided more structural information from the PCI spectra. A multi‐pathway fragmentation was proposed for these ions leading to the protonated phthalic anhydride. DFT methods were used to calculate relative free energies and to determine structures of intermediate ions for these pathways. The first step of the fragmentation of [M + C2H5]+ and [M + C3H5]+ is the elimination of [R? H] from an ester group. The second ester group undergoes either a McLafferty rearrangement route or a neutral loss elimination of ROH. DFT calculations (B3LYP, B3PW91 and BPW91) using 6‐311G(d,p) basis sets showed that McLafferty rearrangement of dibutyl, di(‐n‐octyl) and di(2‐ethyl‐n‐hexyl) phthalates is an energetically more favorable pathway than loss of an alcohol moiety. Prominent ions in these pathways were confirmed with deuterium labeled phthalates. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
2.
Herbert J. Dias Manon Baguenard Eduardo J. Crevelin Vinicius Palaretti Paul J. Gates Ricardo Vessecchi Antnio E.M. Crotti 《Journal of mass spectrometry : JMS》2019,54(1):35-46
We have investigated gas‐phase fragmentation reactions of protonated benzofuran neolignans (BNs) and dihydrobenzofuran neolignans (DBNs) by accurate‐mass electrospray ionization tandem and multiple‐stage (MSn) mass spectrometry combined with thermochemical data estimated by Computational Chemistry. Most of the protonated compounds fragment into product ions B ([M + H–MeOH]+), C ([ B –MeOH]+), D ([ C –CO]+), and E ([ D –CO]+) upon collision‐induced dissociation (CID). However, we identified a series of diagnostic ions and associated them with specific structural features. In the case of compounds displaying an acetoxy group at C‐4, product ion C produces diagnostic ions K ([ C –C2H2O]+), L ([ K –CO]+), and P ([ L –CO]+). Formation of product ions H ([ D –H2O]+) and M ([ H –CO]+) is associated with the hydroxyl group at C‐3 and C‐3′, whereas product ions N ([ D –MeOH]+) and O ([ N –MeOH]+) indicate a methoxyl group at the same positions. Finally, product ions F ([ A –C2H2O]+), Q ([ A –C3H6O2]+), I ([ A –C6H6O]+), and J ([ I –MeOH]+) for DBNs and product ion G ([ B –C2H2O]+) for BNs diagnose a saturated bond between C‐7′ and C‐8′. We used these structure‐fragmentation relationships in combination with deuterium exchange experiments, MSn data, and Computational Chemistry to elucidate the gas‐phase fragmentation pathways of these compounds. These results could help to elucidate DBN and BN metabolites in in vivo and in vitro studies on the basis of electrospray ionization ESI‐CID‐MS/MS data only. 相似文献
3.
Masamichi Sakai Kazumasa Okada Keiichi Ohno Kiyohiko Tabayashi 《Journal of mass spectrometry : JMS》2010,45(3):306-312
Fragmentation of the pyridine ring upon K‐shell excitation/ionization has been studied with gaseous 2‐, 3‐ and 4‐methylpyridine by the electron‐impact method. Ab initio molecular orbital (MO) calculations were also carried out to explore electronic states correlating with specific fragments. Some specific fragmentation channels were identified from the ionic fragments enhanced characteristically at the N 1s edge. Yields of the C2HN+ and C5H5+/C5H6+ ions show that the fission of the N? C2 and C4? C5/C5? C6 bonds of the ring is likely to occur after the N 1s excitation and ionization. Ab initio MO calculations for the 2‐methylpyridine molecule indicate that the dissociation channels to produce these ions are only accessible through the excited states of the parent molecular dication, which can be formed by Auger decays after the N 1s ionization. Fragment ions via hydrogen rearrangement are produced as well, but the rearrangement is not a phenomenon specific to the K‐shell excitation/ionization. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
4.
Gas‐phase fragmentation of γ‐lactone derivatives by electrospray ionization tandem mass spectrometry
Antonio E. M. Crotti Erika S. Bronze‐Uhle Paulo G. B. D. Nascimento Paulo M. Donate Sérgio E. Galembeck Ricardo Vessecchi Norberto P. Lopes 《Journal of mass spectrometry : JMS》2009,44(12):1733-1741
Fragmentation reactions of β‐hydroxymethyl‐, β‐acetoxymethyl‐ and β‐benzyloxymethyl‐butenolides and the corresponding γ‐butyrolactones were investigated by electrospray ionization tandem mass spectrometry (ESI‐MS/MS) using collision‐induced dissociation (CID). This study revealed that loss of H2O [M + H ?18]+ is the main fragmentation process for β‐hydroxymethylbutenolide (1) and β‐hydroxymethyl‐γ‐butyrolactone (2). Loss of ketene ([M + H ?42]+) is the major fragmentation process for protonated β‐acetoxymethyl‐γ‐butyrolactone (4), but not for β‐acetoxymethylbutenolide (3). The benzyl cation (m/z 91) is the major ion in the ESI‐MS/MS spectra of β‐benzyloxymethylbutenolide (5) and β‐benzyloxymethyl‐γ‐butyrolactone (6). The different side chain at the β‐position and the double bond presence afforded some product ions that can be important for the structural identification of each compound. The energetic aspects involved in the protonation and gas‐phase fragmentation processes were interpreted on the basis of thermochemical data obtained by computational quantum chemistry. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
5.
An ion‐neutral complex (INC)‐mediated hydride transfer reaction was observed in the fragmentation of protonated N‐benzylpiperidines and protonated N‐benzylpiperazines in electrospray ionization mass spectrometry. Upon protonation at the nitrogen atom, these compounds initially dissociated to an INC consisting of [RC6H4CH2]+ (R = substituent) and piperidine or piperazine. Although this INC was unstable, it did exist and was supported by both experiments and density functional theory (DFT) calculations. In the subsequent fragmentation, hydride transfer from the neutral partner to the cation species competed with the direct separation. The distribution of the two corresponding product ions was found to depend on the stabilization energy of this INC, and it was also approved by the study of substituent effects. For monosubstituted N‐benzylpiperidines, strong electron‐donating substituents favored the formation of [RC6H4CH2]+, whereas strong electron‐withdrawing substituents favored the competing hydride transfer reaction leading to a loss of toluene. The logarithmic values of the abundance ratios of the two ions were well correlated with the nature of the substituents, or rather, the stabilization energy of this INC. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
6.
7.
Ortho‐hydroxyl effect and proton transfer via ion–neutral complex: the fragmentation study of protonated imine resveratrol analogues in mass spectrometry 下载免费PDF全文
Lei Yue Jing Li Xiaodong Xie Cheng Guo Xinchi Yin Qi Yin Yinjuan Chen Yuanjiang Pan Chuanfan Ding 《Journal of mass spectrometry : JMS》2016,51(7):518-523
The fragmentation pathways of protonated imine resveratrol analogues in the gas‐phase were investigated by electrospray ionization–tandem mass spectrometry. Benzyl cations were formed in the imine resveratrol analogues that had an ortho‐hydroxyl group on the benzene ring A. The specific elimination of the quinomethane neutral, CH2 = C6H4 = O, from the two isomeric ions [M1 + H]+ and [M3 + H]+ via the corresponding ion–neutral complexes was observed. The fragmentation pathway for the related meta‐isomer, ion [M2 + H]+ and the other congeners was not observed. Accurate mass measurements and additional experiments carried out with a chlorinated analogue and the trideuterated isotopolog of M1 supported the overall interpretation of the fragmentation phenomena observed. It is very helpful for understanding the intriguing roles of ortho‐hydroxyl effect and ion–neutral complexes in fragmentation reactions and enriching the knowledge of the gas‐phase chemistry of the benzyl cation. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
8.
V. I. Kadentsev N. G. Kolotyrkina A. A. Stomakhin O. S. Chizhov S. A. Shevelev 《Russian Chemical Bulletin》1997,46(6):1184-1185
Interaction of mononitroalkanes with the trimethylsilyl cation in the gas phase under chemical ionization (CI) conditions
results in the formation of [M+SiMe3]+ ions, which are more stable than the corresponding protonated molecular ions. In the case of 2-nitro-2-methylpropane and
2-nitropentane, fragmentation of the [M+SiMe3]+ ions occurs with the formation of C4H9
+ and C5H11
+ carbocations, respectively. In the case of 1,1-dinitroethane and 1-halo-1,1-dinitroethane, fragmentation of the [M+SiMe3]+ ions occurs with splitting off of a NO2
. radical or an XNO2 molecule (X=H, F, or Cl).
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1232–1234, June, 1997. 相似文献
9.
L. V. Klyba L. K. Papernaya E. R. Sanzheeva A. A. Shatrova E. V. Rudyakova G. G. Levkovskaya 《Russian Journal of Organic Chemistry》2011,47(12):1851-1858
The mass spectra of 1-substituted 3,5-dimethyl-1H-pyrazole-4-carbaldehyde bis(2-hydroxyethyl) dithioacetals and thioacetals were studied for the first time. The main fragmentation
pathways of their molecular ions generated under electron impact and chemical ionization were similar. Primary decomposition
of the molecular ions of bis(2-hydroxyethyl) dithioacetals involves elimination of 2-sulfanylethanol molecule with formation
of the corresponding 1,3-oxathiolane radical cation. Fragmentation of the molecular ions [M]+ · and [M + H]+ derived from 2-(3,5-dimethyl-1H-pyrazol-4-yl)-1,4,6-oxadithiocanes includes cleavage of the eight-membered heteroring and elimination of C4H9OS ·. Substituents in the heteroring of pyrazolecarbaldehydes inhibit decomposition processes related to the aldehyde group. 相似文献
10.
In order to establish the mechanism of CO loss occurring during metastable decomposition of protonated 1-indanone, fragmentations of monocyclic [C9H9O]+ isomers have been studied. These ions of known structure were prepared by CI protonation and fragmentation of the corresponding acids chlorides. It is demonstrated that the wide component of the [MH? CO]+ metastable peak induced by protonated 1-indanone fragmentation is the result of fragmentation of the [C6H5CH2CH2CO]+ isomer ion. 相似文献
11.
The chemical ionization mass spectra of five isomers of C3H6O (acetone, propionaldehyde, oxetane, propylene oxide and allyl alcohol) have been determined using a variety of reagent gases (H2, D2, N2/H2, CO2/H2 and CO/H2). The [C3H7O]+ ions produced by protonation of these isomers undergo very similar reactions to those reported for analogous [C3H7O]+ metastable ions; however, decomposing ions generated by chemical ionization appear to have somewhat higher internal energies. The results of 2H labelling studies (D2 reagent gas or labelled analogues of C3H6O) indicate that protonation occurs mainly on oxygen and are consistent with previous investigations of metastable oxonium ions. The protonated acetone ion is particularly stable, in agreement with the higher activation energies for fragmentation of this isomer than for other [C3H7O]+ structures. As the calculated heat of protonation of C3H6O is reduced by changing the reagent gas, so the extent to which fragmentation occurs decreases. This is discussed in the context of competition between fragmentation and collisional stabilization of the excited [C3H7O]+* ion. It is concluded that on average a large fraction (approaching 1) of the exothermicity of the protonation reaction resides in the [C3H7O]+* ions produced initially. 相似文献
12.
Yu.S. Nekrasov 《Journal of organometallic chemistry》2009,694(12):1807-1812
Under the conditions of electrospray ionization of ferrocenylalkyl azoles FcCH(R)X (Fc-η5-C5H5Fe-η5-C5H4, R - H, Me, XH - 2-methyl imidazole, pirazole) the processes of oxidation, protonation, fragmentation and ferrocenylalkylation to form, molecular ions [М]+, protonated molecules [М+Н]+, ferrocenylalkyl cations [FсCHR]+ and bisferrocenylalkyl azole cations [(FcCHR)2X]+, respectively, take place. Using special experimental techniques (deuterated solvents, saturation of ionic source of an ESI mass-spectrometer by the vapors of solvents, the experiments under the “inverse” ESI conditions when the solvent is subjected to electrospray in the presence of ferrocenylalkyl derivative vapours) and quantum-chemical calculations at the level of the B3LYP/LanL2DZ theory the scheme of the formation of these ions in a gas phase according to the mechanism of “activating protonation” was suggested. it was found that all these ions are formed through the protonation stage, which is taking place mainly in a gas phase. The key stage is the exothermic process of the protonation of the initial compounds by hydroxonium ions giving rise to protonated [M+H]+ molecules which further oxidize and alkylate ferrocenylalkylazoles to form molecular radical cations and bisferrocenylalkyl azole ions [FcCH(Me)-X-CH(Me)Fc]+. The decomposition of protonated ions with the elimination of the azole molecule gives rise to ferrocenylalkyl cations [FсCHR]+ capable in turn of oxidizing and alkylating the initial compounds. 相似文献
13.
Four isomeric thioethers, 2,3-dimethylthiirane ( 1 ), 2-methylthietane ( 2 ), tetrahydrothiophene ( 3 ), and allyl methyl thioether ( 4 ), have been subjected to mass spectrometric analysis in the gas phase, under electron impact (El) and chemical ionization (CI) conditions. The metastable molecular ions M+′ generated from 1-4 under EI (70 eV) conditions give distinct patterns of unimolecular fragmentation, thus indicating that isomer interconversion reactions are slower than dissociation (a possible exception, to some extent, is the case of [M2]+′ and [M2]+′). The change of the relative intensities of some prominent peaks with increasing ion lifetime (decomposition within the ion source, the first, and the second field-free regions of the mass spectrometer) is pointed out. Metastable [MH]+ ions, generated from 1-4 in chemical ionization experiments with CH4, all eliminate H2 and H2S, although in different relative proportions. In addition to these processes protonated 4 also undergoes loss of C2H4 and C3H6, likely from a C-protonated structure. 相似文献
14.
Duan X Luo G Chen Y Kong X 《Journal of the American Society for Mass Spectrometry》2012,23(6):1126-1134
The collisionally activated dissociation mass spectra of the protonated and alkali metal cationized ions of a triazole-epothilone
analogue were studied in a Fourier transform ion cyclotron resonance mass spectrometer. The fragmentation pathway of the protonated
ion was characterized by the loss of the unit of C3H4O3. However, another fragmentation pathway with the loss of C3H2O2 was identified for the complex ions with Na+, K+, Rb+, and Cs+. The branching ratio of the second pathway increases with the increment of the size of alkali metal ions. Theoretical calculations
based on density functional theory (DFT) method show the difference in the binding position of the proton and the metal ions.
With the increase of the radii of the metal ions, progressive changes in the macrocycle of the compound are induced, which
cause the corresponding change in their fragmentation pathways. It has also been found that the interaction energy between
the compound and the metal ion decreases with increase in the size of the latter. This is consistent with the experimental
results, which show that cesiated complexes readily eject Cs+ when subject to collisions. 相似文献
15.
Dr. Michael Capron Dr. Sergio Díaz‐Tendero Sylvain Maclot Dr. Alicja Domaracka Elie Lattouf Dr. Arkadiusz Ławicki Dr. Rémi Maisonny Prof. Jean‐Yves Chesnel Dr. Alain Méry Dr. Jean‐Christophe Poully Dr. Jimmy Rangama Prof. Lamri Adoui Prof. Fernando Martín Prof. Manuel Alcamí Dr. Patrick Rousseau Prof. Bernd A. Huber 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(30):9321-9332
Fragmentation of the γ‐aminobutyric acid molecule (GABA, NH2(CH2)3COOH) following collisions with slow O6+ ions (v≈0.3 a.u.) was studied in the gas phase by a combined experimental and theoretical approach. In the experiments, a multicoincidence detection method was used to deduce the charge state of the GABA molecule before fragmentation. This is essential to unambiguously unravel the different fragmentation pathways. It was found that the molecular cations resulting from the collisions hardly survive the interaction and that the main dissociation channels correspond to formation of NH2CH2+, HCNH+, CH2CH2+, and COOH+ fragments. State‐of‐the‐art quantum chemistry calculations allow different fragmentation mechanisms to be proposed from analysis of the relevant minima and transition states on the computed potential‐energy surface. For example, the weak contribution at [M?18]+, where M is the mass of the parent ion, can be interpreted as resulting from H2O loss that follows molecular folding of the long carbon chain of the amino acid. 相似文献
16.
Mass spectrometric monitoring of oxidation of aliphatic C6–C8 hydrocarbons and ethanol in low pressure oxygen and air plasmas 下载免费PDF全文
Dilshadbek T. Usmanov Lee Chuin Chen Kenzo Hiraoka Hiroshi Wada Hiroshi Nonami Shinichi Yamabe 《Journal of mass spectrometry : JMS》2016,51(12):1187-1195
Experimental and theoretical studies on the oxidation of saturated hydrocarbons (n‐hexane, cyclohexane, n‐heptane, n‐octane and isooctane) and ethanol in 28 Torr O2 or air plasma generated by a hollow cathode discharge ion source were made. Ions corresponding to [M + 15]+ and [M + 13]+ in addition to [M ? H]+ and [M ? 3H]+ were detected as major ions where M is the sample molecule. The ions [M + 15]+ and [M + 13]+ were assigned as oxidation products, [M ? H + O]+ and [M ? 3H + O]+, respectively. By the tandem mass spectrometry analysis of [M ? H + O]+ and [M ? 3H + O]+, H2O, olefins (and/or cycloalkanes) and oxygen‐containing compounds were eliminated from these ions. Ozone as one of the terminal products in the O2 plasma was postulated as the oxidizing reagent. As an example, the reactions of C6H14+? with O2 and of C6H13+ (CH3CH2CH+CH2CH2CH3) with ozone were examined by density functional theory calculations. Nucleophilic interaction of ozone with C6H13+ leads to the formation of protonated ketone, CH3CH2C(=OH+)CH2CH2CH3. In air plasma, [M ? H + O]+ became predominant over carbocations, [M ? H]+ and [M ? 3H]+. For ethanol, the protonated acetic acid CH3C(OH)2+ (m/z 61.03) was formed as the oxidation product. The peaks at m/z 75.04 and 75.08 are assigned as protonated ethyl formate and protonated diethyl ether, respectively, and that at m/z 89.06 as protonated ethyl acetate. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
17.
Chhabil Dass 《Journal of mass spectrometry : JMS》1994,29(9):475-482
The chemistry of glycerol subjected to a high-energy particle beam was explored by studying the mass spectral fragmentation characteristics of gas-phase protonated glycerol and its oligomers by using tandem mass spectrometry. Both unimolecular metastable and collision-induced dissociation reactions were studied. Collision activation of protonated glycerol results in elimiation of H2O and CH3OH molecules. The resulting ions undergo further fragmentations. The origin of several fragment ions was established by obtaining their product and precursor ion spectra. Corresponding data for the deuterated analogs support those results. The structures of the fragment ions of compositions [C3H5O]+, [C2H5O]+, [C2H4O]+. and [C2H3O]+ derived from protonated glycerol were also identified. Proton-bound glycerol oligomers fragment principally via loss of neutral glycerol molecules. Dissociation of mixed clusters of glycerol and deuterated glycerol displays normal secondary isotope effects. 相似文献
18.
Ramesh M Raju B Srinivas R Sureshbabu VV Narendra N Vasantha B 《Journal of mass spectrometry : JMS》2010,45(12):1461-1472
Four pairs of positional isomers of ureidopeptides, FmocNH‐CH(R1)‐φ(NH‐CO‐NH)‐CH(R2)‐OY and FmocNH‐CH(R2)‐φ(NH‐CO‐NH)‐CH(R1)‐OY (Fmoc = [(9‐fluorenyl methyl)oxy]carbonyl; R1 = H, alkyl; R2 = alkyl, H and Y = CH3/H), have been characterized and differentiated by both positive and negative ion electrospray ionization (ESI) ion‐trap tandem mass spectrometry (MS/MS). The major fragmentation noticed in MS/MS of all these compounds is due to ? N? CH(R)? N? bond cleavage to form the characteristic N‐ and C‐terminus fragment ions. The protonated ureidopeptide acids derived from glycine at the N‐terminus form protonated (9H‐fluoren‐9‐yl)methyl carbamate ion at m/z 240 which is absent for the corresponding esters. Another interesting fragmentation noticed in ureidopeptides derived from glycine at the N‐terminus is an unusual loss of 61 units from an intermediate fragment ion FmocNH = CH2+ (m/z 252). A mechanism involving an ion‐neutral complex and a direct loss of NH3 and CO2 is proposed for this process. Whereas ureidopeptides derived from alanine, leucine and phenylalanine at the N‐terminus eliminate CO2 followed by corresponding imine to form (9H‐fluoren‐9‐yl)methyl cation (C14H11+) from FmocNH = CHR+. In addition, characteristic immonium ions are also observed. The deprotonated ureidopeptide acids dissociate differently from the protonated ureidopeptides. The [M ? H]? ions of ureidopeptide acids undergo a McLafferty‐type rearrangement followed by the loss of CO2 to form an abundant [M ? H ? Fmoc + H]? which is absent for protonated ureidopeptides. Thus, the present study provides information on mass spectral characterization of ureidopeptides and distinguishes the positional isomers. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
19.
Chemical ionization mass spectra of six 5,6-dihydro-2-methyl-1,4-oxathiins, and some of the sulfoxides and sulfones derived therefrom, have been determined employing hydrogen, methane and isobutane as reagent gases. The major fragmentation reaction of the protonated molecule, [R′COX·H]+, involves loss of the neutral HX molecule. For the sulfides and sulfones, with X ranging from OH to N(CH3)C6H5, it is observed that the importance of this fragmentation is inversely correlated with the proton affinity of the departing HX molecule in both the H2 and CH4 chemical ionization. For the sulfoxides no consistent correlation is observed and this is attributed to the interference of competing and/or consecutive fragmentation reactions. In the isobutane chemical ionization mass spectra only the protonated molecule is observed for most of the compounds studied. 相似文献
20.
M. Ramesh B. Raju M. George K. Srinivas V. Jayathirtha Rao K. Bhanuprakash R. Srinivas 《Journal of mass spectrometry : JMS》2012,47(7):860-868
The electrospray ionization collisionally activated dissociation (CAD) mass spectra of protonated 2,4,6‐tris(benzylamino)‐1,3,5‐triazine (1) and 2,4,6‐tris(benzyloxy)‐1,3,5‐triazine (6) show abundant product ion of m/z 181 (C14H13+). The likely structure for C14H13+ is α‐[2‐methylphenyl]benzyl cation, indicating that one of the benzyl groups must migrate to another prior to dissociation of the protonated molecule. The collision energy is high for the ‘N’ analog (1) but low for the ‘O’ analog (6) indicating that the fragmentation processes of 1 requires high energy. The other major fragmentations are [M + H‐toluene]+ and [M + H‐benzene]+ for compounds 1 and 6, respectively. The protonated 2,4,6‐tris(4‐methylbenzylamino)‐1,3,5‐triazine (4) exhibits competitive eliminations of p‐xylene and 3,6‐dimethylenecyclohexa‐1,4‐diene. Moreover, protonated 2,4,6‐tris(1‐phenylethylamino)‐1,3,5‐triazine (5) dissociates via three successive losses of styrene. Density functional theory (DFT) calculations indicate that an ion/neutral complex (INC) between benzyl cation and the rest of the molecule is unstable, but the protonated molecules of 1 and 6 rearrange to an intermediate by the migration of a benzyl group to the ring ‘N’. Subsequent shift of a second benzyl group generates an INC for the protonated molecule of 1 and its product ions can be explained from this intermediate. The shift of a second benzyl group to the ring carbon of the first benzyl group followed by an H‐shift from ring carbon to ‘O’ generates the key intermediate for the formation of the ion of m/z 181 from the protonated molecule of 6. The proposed mechanisms are supported by high resolution mass spectrometry data, deuterium‐labeling and CAD experiments combined with DFT calculations. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献