| Popis: |
1H and 13C NMR spectra of aryl esters of propionic acid, acrylic acid, and propiolic acid were systematically examined to find out the substituent effect on the chemical shift. The values of the chemical shift of the carbonyl carbon showed an inverse correlation with the Hammett σ values, and the magnitude of the slope was the largest with the propiolates. The α carbons of acrylates and propiolates also showed an inverse correlation with much smaller values of the slopes than those of the carbonyl carbons; but those of the propionates showed absolutely no correlation. However, the β carbons of acrylates and propiolates showed normal correlation with larger values of the slopes. The signs and the magnitudes of the slopes may be understood by the transmission of the substituent electronic effect through bonds as well as through space. The propiolyloxy group also showed a significantly large effect on the 13C chemical shift values of the benzene ring. |
