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

摘要

Some Si-29 and C-13 NMR studies were performed on 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 sigma(p) and (b) the PM3-calculated total atomic charges. It is inferred that the SiMe(2) sigma-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 SiMe(2) group is a better transmitter of electronic effects than the CH2 group. [References: 43]