Multinuclear NMR study of chlorinated vinylsilanes

Abstract

Silylethylenes of the types (CH 3) 3- n X n SiCHCHCl (I = trans, II = cis), (CH 3) 3- n X n SiCHCCl 2 (III), (CH 3) 3- n X n SiCCl  CCl 2 (IV) and (CH 3) 3- n X n SiCHCHSiX n (CH 3) 3- n (V) ( n = 0-3, X = Cl, OEt, OMe), were studied by 1H, 13C, 29Si and 17O NMR methods. A comparison of the 13C chemical shifts in I–V with those in the corresponding vinylsilanes reveals that the sensitivity of α, β-olefinic carbon resonances to electronic effects of the Si substituents diminishes in the sequence: I > III > II ≈ IV. Various possible coupling constants in I–V were measured. A linear correlation between 1 J(CC) coupling in I–IV and the sum of the electronegativities of the Si substituents was obtained. The different correlations between 1 J( 29Si 13C) and 2 J( 29SiC 1H) involving X = Cl or OR substituents is explained within the framework of the ( p - d) π hypothesis.