Unimolecular dissociation of methylsilylium and monochloromethylsilylium in the gas phase
摘要:
The mechanisms for the lowest energy barrier pathways for unimolecular dissociation of CH3SiH2+ and CH3-Si(Cl)H+ were examined in the gas phase by using Fourier transform mass spectrometry (FIMS). Collision-activated dissociation (CAD) by using sustained ''off-resonance'' irradiation (SORI) was used to determine the lowest energy pathways for dissociation. The lowest energy pathway for decomposition of CH3SiH2+ is dehydrogenation. The mechanism for this dehydrogenation process was investigated by studying the decomposition of CH3SiD2+. Unfortunately, isotopic scrambling by reversible 1,2-hydrogen migrations precede dehydrogenation. Hence, no mechanistic information is obtained from this isotopic labeling experiment. SORI-CAD of CH3SiD2+ yields dehydrogenation as H-2 (0.67) and HD (0.33) with no D2 loss. The lowest energy pathway for dissociation of CH3Si(Cl)H+ is elimination of HCl. In contrast to CH3SiD2+, CH3Si(CI)D+ does not undergo isotopic scrambling upon CAD. SORI-CAD of CH3Si(Cl)D+ yields exclusive elimination of HCl(1,2-elimination) to yield CH2SiD+. Hence, the lowest energy pathway for dissociation of CH3Si(Cl)H+ is 1,2-elimination of HCI. 1,1-Elimination of DCl from CH3Si(CI)D+ to yield CH3Si+ is 38 kcal/mol more favorable than the 1,2-elimination process. Consequently, there must be a prohibitive barrier for the energetically more favorable 1,1-elimination process.
Wlodek; Fox; Bohme, Journal of the American Chemical Society, 1991, vol. 113, # 12, p. 4461 - 4468
作者:Wlodek、Fox、Bohme
DOI:——
日期:——
Unimolecular dissociation of methylsilylium and monochloromethylsilylium in the gas phase
作者:R. Bakhtiar、C. M. Holznagel、D. B. Jacobson
DOI:10.1021/j100151a014
日期:1993.12
The mechanisms for the lowest energy barrier pathways for unimolecular dissociation of CH3SiH2+ and CH3-Si(Cl)H+ were examined in the gas phase by using Fourier transform mass spectrometry (FIMS). Collision-activated dissociation (CAD) by using sustained ''off-resonance'' irradiation (SORI) was used to determine the lowest energy pathways for dissociation. The lowest energy pathway for decomposition of CH3SiH2+ is dehydrogenation. The mechanism for this dehydrogenation process was investigated by studying the decomposition of CH3SiD2+. Unfortunately, isotopic scrambling by reversible 1,2-hydrogen migrations precede dehydrogenation. Hence, no mechanistic information is obtained from this isotopic labeling experiment. SORI-CAD of CH3SiD2+ yields dehydrogenation as H-2 (0.67) and HD (0.33) with no D2 loss. The lowest energy pathway for dissociation of CH3Si(Cl)H+ is elimination of HCl. In contrast to CH3SiD2+, CH3Si(CI)D+ does not undergo isotopic scrambling upon CAD. SORI-CAD of CH3Si(Cl)D+ yields exclusive elimination of HCl(1,2-elimination) to yield CH2SiD+. Hence, the lowest energy pathway for dissociation of CH3Si(Cl)H+ is 1,2-elimination of HCI. 1,1-Elimination of DCl from CH3Si(CI)D+ to yield CH3Si+ is 38 kcal/mol more favorable than the 1,2-elimination process. Consequently, there must be a prohibitive barrier for the energetically more favorable 1,1-elimination process.