Reactivities of 4‐trimethylsilylmethylstyrene and 4‐bis(trimethylsilyl)methylstyrene

Abstract 4‐Trimethylsilylmethylstyrene (1), and 4‐bis(trimethylsilyl)methylstyrene (2) were synthesized and polymerized. The reactivities of 1 and 2 in free radical and nucleophilic reactions are discussed, referring to 1H NMR and UV spectral data. The absolute values of the negative e‐ values were found to be higher than those of styrene and other styrene derivatives such as 4‐methylstyrene. The reactivities of these monomers toward nucleophilic reagents are lower than those of other styrenes. From these investigations it was concluded that the trimethylsilylmethyl group, located at 4‐position of vinylbenzene, exhibits an electron donating effect. As anticipated, the effect of the bis(trimethylsilyl)methyl group is larger than that of the trimethylsilylmethyl group. AM1 calculations showed that the effect is attributable to the σ‐π‐hyperconjugation between the SiC σ‐bond and the π‐electron system of the phenyl ring. The larger effect of 2 as compared with 1 may be explained by additional σ‐π‐hyperconjugation between the second CSi bond in horizontal position and the phenyl π‐orbital in addition to the σ‐π‐hyperconjugation of the first CSi bond in vertical position.