Collision‐induced dissociation of the phenylsilane molecular ion

Abstract

The high-energy collision-induced dissociation of the phenylsilane molecular ion generated by electron ionization has been investigated using tandem mass spectrometry (MS/MS). It was observed that the dissociation of the molecular ion (M(+*)) occurs mainly via [M-H](+), [M-2H](+*), and [M-3H](+), followed by two consecutive losses of C(2)H(2). The structures of the precursors for the [M-CH(3)](+), [M-SiH](+), and [M-SiH(2)](+*) ions are proposed. The data suggest that the molecular ion undergoes rearrangements to several isomers prior to dissociation, including the ion containing a five-membered carbon ring. Reaction mechanisms are proposed for the dissociations via the isomeric molecular ions.

Loss of benzene from methylphenylsilane and dimethylphenylsilane molecular cations

“…The cleavage of the bond between the silicon and the ipso-carbon of the ion-molecule complexes is possible, which will produce the benzene radical cation and/or SiH 2 •+ . These fragment ions appear in the 70-eV electron ionization (EI) mass spectrum of phenylsilane reported previously [8]. Their relative abundances, however, were small and they were not detected in the MID of phenylsilane ion [9], suggesting that the Si C bond cleavage needs high energies and are kinetically less favorable.…”

“…The m/z 106 and 105 ions are produced mainly via the m/z 107 ion. The m/z 53 ion (C 2 HSi + ), which has been observed also in the dissociation of 1a •+ and assigned as HC C Si + in the previous work [8], is produced mainly by ring cleavages via the m/z 106 and 105 ions. The m/z 44 ion is produced by loss of C 6 H 6 , of which mechanism will be discussed below.…”

“…As it is well known, the tropylium ion is produced from the toluene molecular cation as well as the benzylium ion [10][11][12][13]. It has been revealed, however, that the silatropylium ion is not produced from 1a •+ , a silicon analogue of the toluene ion, through the studies by several researchers [5][6][7][8][9]. Such a difference could be understood by the theoretical expectation that the tropylium ion is more stable than the benzylium ion, while the reverse is true for their silicon analogues [9].…”

“…The dissociation of phenylsilane (1a) molecular cation is a good example [2][3][4][5][6][7][8][9]. As it is well known, the tropylium ion is produced from the toluene molecular cation as well as the benzylium ion [10][11][12][13].…”

Fragmentation of methylphenylsilane and trimethylphenylsilane: A combined theoretical and experimental study

“…The process after ionization depends on the energy profile of bond dissociation. The phenylsilane dissociation by electron impact ionization was described in the literature as a typical example of similar compounds [19,20]. The organosilicon molecules are also interesting from a theoretical point of view.…”