NMR-Data from Canadian Journal of Chemistry, 77, 146 (1999)


Structure

This compound has been synthesized and the analytical data have been published in the above mentioned article. The tert.-butyldimethylsilyl group is a frequently occuring protecting group in organic chemistry. A CAS-search using SCIFINDER revealed 207,820 structures, when using this structural fragment as query.


A prediction of the carbon chemical shiftvalues for this protecting group leads to values of -5ppm for the Si-CH3 group, 18ppm for the quarternary carbon and 25ppm for the -CH3 in the tBu-group. (Values rounded, nearly identical values obtained by HOSE and NN calculation using CSEARCH)

When looking into the above mentioned article (Compound #8) we find the following values for the protecting group: 53.27 (SiC(CH3)3), 25.89 (SiC(CH3)3), 18.22 (Si(CH3)2)

Shiftvalues


Carbon position
CSEARCH-HOSE
CSEARCH-NN
Literature
SiC(CH3)3
18.3
18.5
53.27 ppm
SiC(CH3)3
25.9
25.2
25.89 ppm
Si(CH3)2
-5.5
-5.6
18.22 ppm


Obviously there is some misassignment when looking at the signals at 18.22ppm and 25.89ppm respectively. The open question is the remaining signal at 53.27ppm. The only explanation I can offer is - when reading the experimental part carefully - dichloromethane, which was used during the last step of workup.

Within the article there is no numbering scheme for the compounds given - in such a case the naumbering from the nomenclature is usually applied. In this particular case the C-2 (138.29ppm) and C-1 (124.56ppm) [the two aromatic signals which are clearly assigned] should also be reversed - maybe the term 'C-ipso' is with respect to the bromine substitution. At least the data representation is not very 'user-friendly' in the case of the aromatic carbons, whereas the signals of the prtecting group are definitely wrong.


Page written by:   Wolfgang.Robien(-at-)c13nmr.at
Page online since:  March 4th, 2008