Metastable and collision-induced fragmentation studies of all C4H12Si+ isomers; a systematic study of structure-reactivity relations

Metastable ion (MI) and collision-induced dissociation (CID) mass spectra have been recorded and compared for all nine C4H12Si(+.) isomers. The (Me)4Si(+.), t-BuSiH 3 (+.) , s-BuSiH 3 (+) , and (Me)2EtSiH(+.) isomers have unique MI and CID mass spectra. The MI mass spectra, including the kinetic energy release values, of (Me)(i-Pr)SiH 2 (+.) and (Me)(n-Pr)SiH 2 (+.) are identical, which implies isomerization. MI data also suggest that a fraction of the n-BuSiH 3 (+.) ions rearrange into branched (Me)2EtSiH(+.) ions and a fraction of the n-BuSiH 3 (+.) ions rearrange into branched s-BuSiH 3 (+.) ions. A comparison with the isomeric C5H 12 (+.) pentanes reveals a crucial difference: H2 loss occurs for n-BuSiH 3 (+.) , i-BuSiH 3 (+.) , s-BuSiH 3 (+.) , (Me)(n-Pr)SiH 2 (+.) , (Me)(i-Pr)SiH 2 (+.) , and Et2SiH 2 (+.) , but not for any of the C5Hi 12 (+.) isomers. Generation of four- or five-membered silicon containing rings is suggested for H2 loss from the C4H12Si(+.) silanes.