d-Orbital effects in silicon substituted π-electron systems. Part XII. Some spectroscopic properties of alkyl and silyl acetylenes and polyacetylenes

Abstract

Vertical ionization energies, characteristic vibrational frequencies, ¹H n.m.r. signals, and electronic transitions are reported for acetylenes X·[CC]_n·X (n= 1, 2, 3; X = H, CMe₃, CH₂·SiMe₃, SiMe₃). Comparison with the corresponding data of ethylene and butadiene derivatives indicates stronger electron back-donation to silicone Si â†� C_π which is interpreted as being due to interactions with both of the perpendicular acetylene π-components. The inductive polarization +l(SiR₃) > +/(CR₃) can be estimated from the substituent effect of CH₂·SiR₃ groups.