PUB - Publikationen an der Universität Bielefeld

The equilibrium structure (re) of gaseous 1,4-bis(trimethylsilyl)-1,3-butadiyne (& Scy;& Ncy;3)3SiCCCCSi(& Scy;& Ncy;3)3 (1) has been determined by a synchronous GED/MS experiment. The electronic structures of 1, as well as of (& Scy;& Ncy;3)2CCCCCC(& Scy;& Ncy;3)2 (2) and PhCCCCPh (3), which differ in the nature of the terminal groups, are described using the NBO and QTAIM methods. Based on the lengths, orders and ellipticity parameters of the bonds, the linear & Scy;& Scy;& Scy;& Scy; fragment in 1 was described as a polyyne, in 2 as a cumulene, and in the planar compound 3 with pi-conjugated Ph groups as a polyyne with a small ellipticity of the & Scy;equivalent to & Scy; bonds. The molecular and electronic structures of the molecular ions [1]+, [2]+, [3]+ and other ions recorded in the EI mass spectrum of 1 were calculated at the B3LYP/cc-pVTZ level of theory. A comparison of the structural parameters of 1, 2 and 3 and the corresponding ions indicates the possibility of modifying the nature of a linear carbon chain both by ionization and by changing the terminal substituents.