Mass Spectra of Alkylsilanes 2. Methylpropylsilane, Dimethylpropylsilane, Trimethylpropylsilane, and Methylpentylsilane

Abstract

We have studied the fragmentation of four alkylsilanes (CH₃SiH₂C₃H₇, (CH₃)₂SiHC₃H₇, (CH₃)₃SiC₃H₇, CH₃SiH₂C₅H₁₁) under EIMS. The characteristic ions of [M-H]⁺, [M-H₂]^+·, m/z 73 and m/z 45 appeared from methylpropylsilane and methylpentylsilane in a similar manner as the fragmentation of butylmethylsilane reported in a previous paper. From the results of deuterium labelled compounds it was confirmed that [M-H]⁺ is produced by eliminating an H-atom on Si-atom. It was also suggested that [M-H₂]^+· is produced by eliminating two H-atoms on Si-atom with the H/D scrambling. The ion of m/z 73 is stabilized by σ-π conjugation. The ion of m/z 45 is mainly formed as the secondary scission ion. By replacing an H-atom with a methyl group on Si-atom the mass spectra of the resulting alkylsilanes become similar to those of the corresponding alkanes.