13C nuclear magnetic resonance study of -polarization in 3- and 4-substituted benzamides and N-chlorobenzamides
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abstract
The substituent effect on the carbonyl carbon [C()] 13C chemical shift in 3- and 4-substituted benzamides and N-chlorobenzamides has been studied in (CD3)2SO. Chlorine shields the carbonyl carbon. A cross correlation was carried out for C() and the carbonyl carbon in N-chlorobenzamides is less sensitive to substituents than in the benzamides. The dual substituent parameter method indicated a significant diminution in the -polarization effect (1) in N-chlorobenzamides compared to benzamides. This is in contrast to other carbonyl systems where 1 has been found to be essentially independent of the substituent attached to the carbonyl carbon. It is concluded that -polarization in benzamide and its derivatives is more sensitive to the substituent attached to the carbonyl carbon than in the other classes of aromatic carbonyl compounds studied to date.
