Trimethylsilyl transfer during electron ionization mass spectral fragmentation of some omega-hydroxycarboxylic and omega-dicarboxylic acid trimethylsilyl derivatives and the effect of chain length

The electron ionization (EI) mass spectral fragmentation of omega-hydroxycarboxylic and omega-dicarboxylic acid trimethylsilyl derivatives was investigated. The mass spectra of these compounds exhibited fragment ions resulting from classical fragmentation of the trimethylsilyl ether and ester groups, and others resulting from the interactions between the two functionalities (m/z 147, 204, 217, [M-31](+) and [M-105](+) in the case of omega-hydroxycarboxylic acid derivatives and m/z 147, 204, 217 and [M-131](+) in the case of omega-dicarboxylic acid derivatives). Several fragmentation pathways were proposed to explain the formation of these different fragment ions. It is proposed that the ions at m/z 204 and 217 are formed via an initial trimethylsilyl transfer between the ether and the ester group or between the two ester groups. This transfer appeared to be more favoured in the case of omega-dicarboxylic acid derivatives and to be dependent on the chain length. A more efficient transfer was in fact observed for compounds with a relatively long alkyl chain. In the case of shorter omega-hydroxycarboxylic and omega-dicarboxylic acid trimethylsilyl derivatives the formation of the ions at m/z 204 and 217 suffers strongly from competition from production of the ion at m/z 147.