METASTABLE AND COLLISION-INDUCED FRAGMENTATION STUDIES OF ALL C4H12SI- A SYSTEMATIC STUDY OF STRUCTURE-REACTIVITY RELATIONS( ISOMERS )

Metastable ion (MI) and collision-induced dissociation (CID) mass spec tra have been recorded and compared for all nine C4H12Si+. isomers. Th e (Me)4Si+., t-BuSiH3+., s-BuSiH3+., and (Me)2EtSiH+. isomers have uni que MI and CID mass spectra. The MI mass spectra, including the kineti c energy release values, of (Me)(i-Pr)SiH2+. and (Me)(n-Pr)SiH2+. are identical, which implies isomerization. MI data also suggest that a fr action of the Et2SiH2+. ions rearrange into branched (Me)2EtSiH+. ions and a fraction of the n-BuSiH3+. ions rearrange into branched s-BuSiH 3+. ions. A comparison with the isomeric C5H12+. pentanes reveals a cr ucial difference: H-2 loss occurs for n-BuSiH3+., i-BuSiH3+., s-BuSiH3 +., (Me)(n-Pr)SiH2+., (Me)(i-Pr)SiH2+., and Et2SiH2+., but not for any of the C5H12+. isomers. Generation of four- or five-membered silicon containing rings is suggested for H-2 loss from the C4H12Si+. Silanes.