Predominance of resonance over polar effects on1H,13C and15N NMR substituent chemical shifts inN-arylglycines

1H, 13C and 15N NMR spectra of the ring-substituted N-phenylglycines (1) and their ethyl esters (2) were measured in DMSO-d6. The chemical shift determinations and assignments are based on modern inverse 2D techniques (HMQC, HMBC). Dependences between chemical shifts and substituent constants show that the substituent effect is well transmitted to some side-chain atoms. There is a good correlation between δN1H and linear combinations of the inductive, σI, and resonance substituent constants, σR(-), for compounds 2. Similar results were obtained when the carbonyl carbon chemical shifts in both Series 1 and 2 were related to the substituent constants. Excellent linear dependences were obtained for nitrogen chemical shifts. The correlation coefficient for the linear dependence δ15N vs. linear combination of inductive and resonance substituent constants is high and it becomes even higher when a correction for the solvent effect is included. In general, the contribution of resonance to chemical shifts is much higher than that of polar effects. The results obtained show NHCH2CO2R to be a strong electron donor. © 1998 John Wiley & Sons, Ltd.