Premium
Metastable ion study of organosilicon compounds. Part XIII: dimethoxydimethylsilane, (CH 3 ) 2 Si(OCH 3 ) 2 , and dimethoxymethylsilane, CH 3 SiH(OCH 3 ) 2
Author(s) -
Tajima Susumu,
Sekiguchi Osamu,
Watanabe Yuko,
Nakajima Satoshi,
Takahashi Yutaka
Publication year - 2001
Publication title -
journal of mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 1076-5174
DOI - 10.1002/jms.184
Subject(s) - chemistry , electron ionization , organosilicon , polyatomic ion , thermochemistry , ion , mass spectrum , molecule , dimethoxyethane , fragmentation (computing) , analytical chemistry (journal) , mass spectrometry , ionization energy , ionization , organic chemistry , electrode , chromatography , computer science , electrolyte , operating system
Unimolecular metastable fragmentations of dimethoxydimethylsilane, (CH 3 ) 2 Si(OCH 3 ) 2 (MW 120, 1 ), and dimethoxymethylsilane, CH 3 SiH(OCH 3 ) 2 (MW 106, 2 ), upon electron impact ionization have been studied by means of mass‐analyzed ion kinetic energy (MIKE) spectrometry and the D‐labeling technique in conjunction with thermochemistry. The results have been compared with those of the corresponding carbon analogues, 2,2‐dimethoxypropane, (CH 3 ) 2 C(OCH 3 ) 2 (MW 104, 3 ) and 1,1‐dimethoxyethane, CH 3 CH(OCH 3 ) 2 (MW 90, 4 ). In analogy with the cases of 3 and 4 , both molecular ions from 1 and 2 are formed at very low abundance at 70 eV, and begin to decompose by the expulsion of the substituents (H, CH 3 or OCH 3 ) on the central silicon atom. These decompositions are followed by the loss of a formaldehyde molecule (CH 2 O), as commonly observed in the mass spectra of methoxysilanes. Further, an ethylene (C 2 H 4 ) or a dimethyl ether (CH 3 OCH 3 ) molecule loss is observed in the fragmentation of some intermediate ions generated from 1 +· and 2 +· , but the mechanisms are different than those in the cases of 3 and 4 . Some of these fragmentations are also different than those reported previously. The relative abundance of the ions in many MIKE spectra is explained by the extension of the Stevenson–Audier rule. The reaction, which is in contrast to the rule, however, is rationalized by the energy of the transition state for the reaction, estimated by semi‐empirical molecular orbital calculation. The peak at m / z 59 from 2 +· consists only of CH 3 OSi + ion, whereas the peak from 1 +· consists of two different ions, CH 3 OSi + and (CH 3 ) 2 Si + H. The ions CH 3 OSi + from 1 +· and 2 +· are generated by at least two and three separate routes respectively. Copyright © 2001 John Wiley & Sons, Ltd.