Abstract
17O NMR spectra for 44ortho-,meta- andpara-substituted phenyl and alkyl benzoates (C6H5CO2C6H4-X, C6H5CO2R) at natural abundance in acetonitrile were recorded. Substituent effects on the17O NMR chemical shifts, δ(17O), of the carbonyl oxygen and the single-bonded phenoxy (OPh) and alkoxy (OR) oxygens have been studied. The δ(17O) values of the carbonyl oxygen forparaderivatives showed a good correlation with the σ° constants. The δ(17O) values of carbonyl oxygen fororthoderivatives were found to be described well with the Charton equation containing the inductive, σI, resonance, σ°R, and steric,EsB, substituent constants in case the data treatment was performed separately for electron-donating +Rand electron-attracting –Rsubstituents. The electron-donating +Rorthoandparasubstituents in substituted benzoates caused shielding and the electron-withdrawing –Rsubstituents produced deshielding of the O signal. The steric interaction oforthosubstituents with the ester group decreased the electron density at the carbonyl oxygen. In alkyl benzoates the δ(17O) values were found to be described well with the inductive, σI, and the steric,EsB, substituent constants.
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