The mechanism of methyl loss from ionized methoxypentamethyldisilane: anchimeric assistance versus direct bond cleavage.

J. Mass Spectrom. Soc. Jpn.

2003

It is summarized that the fragmentation and structure of several organic ions, including organosilicon and organofluorine ions, have been investigated by using ion kinetic energy (IKE) spectrometry, mass-analyzed ion kinetic energy (MIKE) spectrometry, D-labeling technique and thermochemistry. Further, several new methods, such as collision energy-dependent collision-induced dissociation (CID) spectra are described. ῒ ῍ ῐQῘῥQQQῖῌ ̮QQQῤ̰ῪQ῝̯QQ̰Q̱ ῥ̯Qῌ ̮̰ῧQQQQῥQQ΅ΰQ̯̮Ύ ̰ CID ῥQQ̮̰ῌ p-´ῼ ῼ ῳ ̮̰ῥ

“…Mechanism of the CH3 loss from the molecular ion of methoxypentamethyldisilane. 92) Scheme 8. Mechanism of the CH3 loss from the molecular ion of trimethylsilylmethanol.…”

Section: ὶῥῥῦ΅̰̮ύῡῗῦQqῥ῎̳΅̯̰ῡ῞ύ῍mentioning

confidence: 99%

Studies of Fragmentation and Structure of Several Organic Ions by Using MIKE Spectrometry and Thermochemistry

J. Mass Spectrom. Soc. Jpn.

2003

“…This observation demonstrates that the methyl loss from the ester function is favored in the molecular ions of 1 with a low internal energy, whereas in the ions with a high energy, the other methyl loss is favored. The former reaction, which includes the cleavage of the oxygen-carbon bond, is, in general, a disfavored reaction, and is accompanied by a large KER [25]. This metastable CH 3 loss would be initiated from the ion that possesses the formal positive charge on the oxygen atom of the methoxy group [pathway (a) in Scheme II] [ As shown in Figure 2c, the ion at 111 / : 61 for 1 shifts to 11/ / z 62 for 1-0-dt.…”

Section: Fragmentation Of Molecular Ionmentioning

confidence: 99%

Fragmentation of the metastable molecular ion of methyl lactate: The formation of oxygen-protonated methanol [CH₃OH₂]⁺ involving double hydrogen atom transfers

J. Am. Soc. Mass Spectrom.

Nagai

Sekiguchi

et al. 1995

The spontaneous unimolecular dissociation reaction of methyl lactate (1) ionized by electron impact was investigated by a combination of mass-analyzed ion kinetic energy spectrometry and deuterium labeling. The metastable ions 1(+·) decompose in a variety of ways: four fragment peaks are observed at m/z 89, 76, 61, and 45, which correspond to the losses of ĊH3, CO, CH3ĊO, and ĊOOCH3, respectively. Double hydrogen atom transfer occurs in the third reaction.The source-generated m/z 61 ions decompose into oxygen-protonated methanols at m/z 33 ([CH3OH 2 (+) ]) by the loss of CO with double hydrogen atom migration. Both hydroxyl and methyne hydrogen atoms in 1 (+·) are present in the resultant protonated methanols.

Metastable ion study of organosilicon compounds part II—hexamethyldisiloxane

Tobita

Okada

et al. 1990

Org. Mass Spectrom.

Unimolecular reactions of the metastable silicenium ion (CH,),SiOSi(CH,), + generated by dissociative ionization of hexamethyldisiloxane were investigated by mass-analysed ion kinetic energy (MIKE) spectrometry. The characteristic fragmentations observed were losses of CH, and (CH,),Si=O molecules. Complete scrambling of all methyl groups prior to these reactions was found by investigating the MIKE spectra of deuterium labelled analogues (CD,),SiOSi(CH&* and (CH,),SiOSi(CD,),+. The loss of methane was accompanied by a large kinetic energy release (To.5 = 482 meV). Tbe MIKE spectra of silicenium ions were compared with those of their carbon analogues. The most predominant reaction of metastable (CH,),COC(CH,), + ion was the loss of CH,=C(CH,), leading to protonated acetone. Significant differences between the ion fragmentation characteristics of silicon and carbon compounds were found.