Mass spectra of sila-cyclobutane and -cyclobutene derivatives

Abstract

The mass spectra of (i) silacyclobutane and some 1,1-disubstituted derivatives containing chloro-, methyl, or methoxy-groups, (ii) 1,1,2-trimethyl-1-silacyclobutane, and (iii) 1,1-dimethyl-1-silacyclopentane are characterised by reasonably abundant parent molecular ions P⁺˙ and a fragmentation scheme dominated by the elimination of ethylene from P⁺˙. The cleavage of a Si–C ring bond leading to three-co-ordinate silicon ions is an important first step in the fragmentation of types (i) and (ii). For R₃M[graphic omitted]H₂(R₃M = Ph₃Si, Ph₃Ge, or Me₃Sn), P⁺˙ ions are also abundant but the elimination of ethylene is unimportant. Most of the major fragment ions observed are produced with cleavage of the M–Si bond. Alternative fragmentation paths to ethylene elimination are also preferred for 1,1-dimethyl- and 1,1-diphenyl-1,2-dihydro-1-silacyclobutabenzene and 1,1,3,3-tetramethyl-1,3-disilacyclobutane: the most important involve loss of Me˙ from the methyl compounds and benzene from the phenyl derivative: abundant P⁺˙ ions are observed.