ISSN:
0749-1581
Keywords:
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
15N Substituent chemical shifts (measured at natural abundantc at 0.4 M concentration) and calculated (ab initio, STO-3G) electron densities at the nitrogen and oxygen (or sulphur) are reported for series of para and meta-substituted benzamides and thiobenzamides with NMe2, NH2, OMe, NHCOMe, F, Cl, Br, I, Me, H, COMe, COOMe, CF3, CN, NO2, CONH2 and CSNH2 substituents. The 15N shift are very sensitive to the substituent effects. The dual substituent parameter method shows excellent correlations of 15N shifts against substituent field and resonance effects, with the sensitivity in the thiobenzamides being double that in the benzamides. In contrast, calculated π-electron densities at the nitrogen show the same sensitivity to substituents in both series. The 15N shifts correlate well with the calculated π-electron densities at the nitrogen; however, estimates of the shielding based on local electron densities (described in Pople's independent electron model) cannot account for the increased sensitivity to the substituent effects observed for 15N chemical shifts of thiobenzamides. It is suggested that non-local shielding from sulphur and oxygen are responsible for the chemical shift trends.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/mrc.1260240917
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