TRANSMISSION OF ELECTRONIC EFFECTS VIA A SIME2 SPACER IN 4-MONO-SUBSTITUTED AND 4,4'-DISUBSTITUTED DIPHENYLDIMETHYLSILANES - SI-29 AND C-13NMR-SPECTROSCOPY AND PM3 SEMIEMPIRICAL CALCULATIONS

Some Si-29 and C-13 NMR studies were performed on series of 4-substitu ted phenyltrimethylsilanes and 4-substituted and 4,4'-disubstituted di phenyldimethylsilanes. Within each series linear relationships are fou nd between the chemical shifts and (a) the Hammett substituent constan ts sigma(p) and (b) the PM3-calculated total atomic charges. It is inf erred that the SiMe(2) sigma-type spacer weakly mediates substituent e ffects in the ground state via a bond polarization mechanism. A compar ison with available data for 4-substituted and 4,4'-disubstituted diph enylmethanes shows that the SiMe(2) group is a better transmitter of e lectronic effects than the CH2 group.