Transmission of electronic effects via a SiMe2 spacer in 4-mono- and 4,4'-disubstituted diphenyldimethylsilanes: 29Si and 13C NMR spectroscopy and PM3 semi-empirical calculations

Article abstract of DOI:10.1016/0022-328X(95)05473-3

Some 29Si and 13C NMR studies were performed of series of 4-substituted phenyltrimethylsilanes and 4-substituted and 4,4'-disubstituted diphenyldimethylsilanes.Within each series linear relationships are found between the chemical shifts and (a) the Hammett substituent constants ?_p and (b) the PM3-calculated total atomic charges.It is inferred that the SiMe2 ?-type spacer weakly mediates substituent effects in the ground state via a bond polarization mechanism.A comparison with available data for 4-substituted and 4,4'-disubstituted diphenylmethanes shows that the SiMe2 group is a better transmitter of electronic effects that the CH2 group. Keywords: Silicon; 29Si NMR; 13C NMR; Substituent effects; MO calculations