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 1 H, 13 C, 29 Si and 17 O NMR methods. A comparison of the 13 C 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 ( 29 Si 13 C) and 2 J ( 29 SiC 1 H) involving X = Cl or OR substituents is explained within the framework of the ( p - d ) π hypothesis.