ISSN:
0030-4921
Keywords:
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Proton and 13C NMR data are presented for six different compounds containing the fragment C6H5—C—CH2SiMe3. In a number of instances it was observed that, in the 1H NMR spectrum, the SiMe3 groups had a chemical shift significantly upfield from internal tetramethylsilane (δ = -0·14 to -0·36). These unexpected upfield chemical shifts of the SiMe3 groups are suggested to result from the predominance, on a time averaged basis, of conformations which place the methyl groups attached to silicon in the face of an aromatic ring. The preference for such conformations is, in turn, the result of rotational preferences exhibited by the ‘flat’ aromatic ring. These results suggest that conformational analysis of systems containing a phenyl ring should take more explicit account of the fact that the preferred orientation of this phenyl ring can have a profound influence on the conformation adopted by the remainder of the molecule. In addition, the preferred conformation of the phenyl ring can have a significant effect upon the observed 1H NMR chemical shifts, while the 13C chemical shifts are relatively insensitive to conformational factors and can be explained by well-known substituent effects previously delineated for all-carbon systems.
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/mrc.1270080110
