Hydrogen and trimethylsilyl transfers during EI mass spectral fragmentation of hydroxycarboxylic and oxocarboxylic acid trimethylsilyl derivatives

Abstract

This paper, describing electron ionization mass spectral fragmentation of some hydroxycarboxylic and oxocarboxylic acid trimethylsilyl derivatives, focuses on the formation of fragment ions resulting from the interactions between the two functionalities of these compounds. These interactions result in the formation of fragment ions at [CH 2 ilylation is by far the major derivatization procedure for GC/MS analyses [1][2][3]. Silyl derivatives are formed when active proton displacement (in ϪOH, ϪSH, or ϪNH groups) by an alkylsilyl group occurs. The most common silylation procedure is trimethylsilylation. Trimethylsilyl derivatives combine thermal stability and high volatility. In general, electron ionization (EI) mass spectra of trimethylsilyl ethers or esters exhibit a significant [M Ϫ 15] ϩ ion formed by loss of a methyl group bonded to silicon, which is very useful in determining the molecular mass. It is very important to note that EI mass spectra of trimethylsilyl derivatives may be employed not only for molecular weight determinations, but also for structural deductions [4].Trimethylsilyl group migrations during EI fragmentation process are common [5,6] and take place by means of ion-neutral complexes [7]. These rearrangements are generally considered useful for deducing structures of unknown spectra [8]; however, in some cases, misleading conclusions may be drawn. Though trimethylsilyl group migrations usually occur through five-to eight-member-ring transition states [9], intense long-range migration of the trimethylsilyl group was previously observed in the case of trimethylsilyl derivatives of some steroid compounds [8, 10 -13]. The capability of the trimethylsilyl group to migrate over a wide range of distances was also demonstrated in the case of semirigid or rigid molecules [5]. Recently, a significant transfer of trimethylsilyl group towards the carbonyl group was also observed during EI fragmentation of the trimethylsilyl derivatives of long-chain -hydroxycarboxylic and -dicarboxylic acids [14], showing that such migrations may also occur in the case of nonrigid structures.Hydrogen transfers between distant functionalities during EI fragmentation processes are also well known [6,15,16], for this reaction hydrogen activation is needed and is caused by groups such as keto, amino, ether, trimethylsilyloxy, as well as by chain branching and unsaturation.In the present work, which is a part of a more general study of the synergistic effects during EI mass fragmentation of polyfunctional compounds [14,[17][18][19], we describe EI mass spectral fragmentation of several hydroxycarboxylic and oxocarboxylic acid trimethylsilyl derivatives, which involves trimethylsilyl and hydrogen transfers.The characterization of such compounds appears to be of great environmental importance [20,21]. Indeed, it was previously demonstrated that autoxidative processes could induce a bias during alkenone-based paAddress reprint requests to Dr.

Gas chromatography/mass spectrometry and pyrolysis-gas chromatography/mass spectrometry for the chemical characterisation of modern and archaeological figs (Ficus carica)

“…The peaks at m/z 331, 317, 303, 289 and 275 are due to the fragmentation (shown in Fig. 2a) from the ␣-cleavage relative to the trimethylsilyloxy ether group [27] of the various co-eluted hydroxy acids.…”

Mass spectral fragmentation of trimethylsilylated small molecules

“…Rearrangement fragmentation rules discussed above for TMS derivatives of long chain terminal diols also apply to many mass spectral patterns of TMS derivatives of long chain terminal dicarboxylic acids. Substructures of typical characteristic fragment ions shown in Figure have been reported multiple times in the literature (Draffan, Stillwell, & McCloskey, ; Diekman, Thomson, & Djerassi, ; Rontani & Aubert, ; Rontani & Aubert, ). Some of these diagnostic ions have the same unit masses and same substructures as the ions mentioned in the alcohols section, like m/z 103.058.…”

“…Carboxylic acids can bear additional moieties that impact overall fragmentation patterns. The electron ionization mass spectral fragmentations of oxocarboxylic and hydroxycarboxylic acid trimethylsilyl derivatives have been investigated (Petersson, ; Rontani & Aubert, , ). While many fragment ions of these compounds can be readily explained by typical fragmentation of the TMS ether and ester groups, other fragments result from H or TMS transfers between two functionalities of the molecule.…”

GC-MS Study of Mono- and Bishaloethylphosphonates Related to Schedule 2.B.04 of the Chemical Weapons Convention: The Discovery of a New Intramolecular Halogen Transfer

“…Similar to the results for compounds 1-12, the elimination of the methyl radical (M-15) that forms product-ions as 25 (Scheme 2, X = H) followed by the loss of an ethylene molecule leads to the base peaks with structure identical to 28. The EI mass spectra of all bisHAPs studied (13-24) lacked the odd-electron molecular ions (Tables 2 and 3, SF [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40]. The molecular masses of these compounds were confirmed by GC/ MS(CI) (SF 41-43).…”

“…Therefore, it seems less probable than the proposed mechanism pathway in Scheme 3. It is remarkable that although some heteroatom transfers have been reported as examples of the hetero McLafferty rearrangement [35][36][37][38][39], no data for similar iodine consecutive transfers have been described in the literature.…”