Springer Online Journal Archives 1860-2000
Chemistry and Pharmacology
Abstract The UV spectra of chains with links of the same type (including SiR2, GeR2, SnR2) show a direct relation of chain length to bathochromic shift of the first strong band, whose wavelength λ1 tends to a limiting value. This tendency can be described approximately via MO and via the model of an electron in a potential box. The first trend is due to nonuniformity in the potential, while the second is due to the values of the resonance integrals for interaction between adjacent bonds. It would seem that interaction between more distant bonds is of secondary importance. The results indicate that the additive scheme is rather crude even for saturated compounds. There is no very pronounced difference between polyenes and compounds whose chains consist of σ-bonds as regards the effects of interaction between groups. The degree of coupling between parts of the chain runs in the sequence CR 2〈 SiR 2, GeR 2〈CH CH. A benzene ring adjacent to a chain of Si atoms shows a marked change in the spectrum of the benzene part; this does not occur with alkylbenzenes and compounds having only one Si atom (PhSiR3). It seems that heavy atoms affect a π-bond system in much the same way via a SiH2 group as via a CH2 group.
Type of Medium: