An unexpected methyl loss observed in electron ionization of chalcones

Abstract

A careful analysis of the electron ionization mass spectra of chalcones reveals the presence of [MÀ15]Á and [MÀ16] ions which, by collision experiments, accurate mass measurements and deuterium labelling have been proved to originate by primary methyl and methane loss respectively. These findings suggest the existence of a population of molecular ions of chalcone exhibiting a structure different from the dibenzocycloheptadienone structure proposed in the literature. # 1998 John Wiley & Sons, Ltd. Received 30 October 1997; Revised 1 December 1997; Accepted 2 December 1997 Rapid Commun. Mass Spectrom. 12, 139-143 (1998 Previous researches on the mass spectrometric behaviour of flavonoids (in particular on flavones 1 , flavanones 2 , naphtoflavones 3 and chalconoids 4,5 ) led us to describe new fragmentation processes and some decomposition mechanisms different from those previously suggested. [6][7][8][9][10][11][12] In particular, in the case of chalcone (1) and some of its derivatives, structure a of Scheme 1 for the [MÀH] species was proved on the basis of metastable ion studies, collisional experiments and 2 H and 13 C-labelled compounds. The presence of this tricyclic structure, containing a sevenmembered ring, was confirmed in most of the flavonoids investigated.In the present paper we report further investigations on some EI-generated fragments of chalcone which, though scarcely abundant, represent interesting decomposition products because they provide an indication of M Á and [MÀH] ions of chalcone with a structure different from those already proposed. EXPERIMENTALMass spectrometric measurements were performed using a MAT112S (Varian MAT, Bremen, Germany) magnetic sector instrument and an ITMS (Finnigan MAT, San José, CA, USA) ion trap instrument.In the former case an ionization energy of 70 eV (700 mA) was employed, with an ion source temperature of 200°C and a direct sample inlet temperature between 130 and 150°C. For high resolution measurements, peak matching was used with a precision of 20 ppm and a resolution better than 6000 in the 10% valley definition. For the measurements of all deuterated species, the ion source was always carefully equilibrated with deuterium oxide. The absolute pressure was lower than 5 Â 10 À6 Torr (1 Torr = 133.3 Pa). The ITMS was operated 13 at a fundamental RF drive frequency of 1.1 MHz. Electron impact spectra were generated at an average electron energy of 70 eV. Helium was used as a bath gas at an uncorrected gauge pressure of 1.0 Â 10 À4 Torr. For the analysis of product ions, the precursor ion was selected using the tandem mass spectrometry (MS/MS) scan function and dynamically programmed scans as described previously. 4 Chalcone (1) was synthesized and purified according to the literature. 4 Its purity level (99%) was checked by gas chromatography/mass spectrometry (GC/MS) and the only impurities present were benzaldehyde and acetophenone employed as synthons for 1. RESULTS AND DISCUSSIONThe mass spectrum of chalcone has already been published and its EI-induc...

Letter: Electron Ionization-Induced Fragmentation of New Thiochalcone Derivatives

“…Decomposition of the molecular ions of 5-20 also proceeds by charge-site-initiated inductive cleavage of the S-C sp3 bond, providing l even-electron ions, observed in the EI/MS spectra of the compounds studied. In the series of derivatives with the five carbon atoms in the alkyl chain (6, 10, 14 and 18), a very highly stable bicyclic form of even-electron fragment ions l, containing quater- It should be pointed out that analysis of EI mass spectra is the best method for distinguishing isomeric (E)-4-piperydynealkylthiochalcones (6,7) and (E)-4-(4-methyl) piperydynealkylthiochalcones (9,10). Compounds 6,7 may be differentiated from their isomeric compounds 9,10 on the basis of the presence, as the base peak of the spectra, of the [C 6 H 12 N] + even-electron ion at m/z 98.…”

“…6,7 The mass spectral fragmentation of various substituted derivatives of chalcone has previously been studied. [8][9][10][11][12][13] The main aim of the present work was to establish the mass spectrometric fragmentations of new (E)-4-chalconylothioalkyl-substituted derivatives of piperidinie (5-8), 4methylpiperidine (9)(10)(11)(12), morpholine (13)(14)(15)(16)) and piperazine (17-20) as well as (E)-4-bromoalkylthiochalcones (1-4) being substrates of the former compounds ( Figure 1). This investigation was also undertaken to find out whether it is possible to differentiate between the isomeric N-(E)chalconylothioalkyl-substituted piperidines (6,7) and N-(4methyl)-piperidines (9,10) on the basis of electron impact (EI) mass spectrometric analysis.…”