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.
记录了在乙腈中的自然丰度下44个邻、间和对位取代苯基和烷基苯甲酸酯(C6H5CO2C6H4-X,C6H5CO2R)的17O NMR光谱。研究了取代基对羰基氧和单键的苯氧基(OPh)和烷氧基(OR)氧的17O NMR化学位移δ(17O)的影响。对于对位衍生物的羰基氧的δ(17O)值与σ°常数呈良好的相关性。发现如果对于电子捐赠+R和电子吸引-R取代基分别进行数据处理,则对于对位衍生物的羰基氧的δ(17O)值可以用包含电感σI、共振σ°R和空间位阻EsB取代基常数的Charton方程来描述。取代苯甲酸酯中的电子捐赠+R对于邻、对位取代基引起屏蔽,而电子吸引-R取代基则导致O信号失屏蔽。邻位取代基与酯基的空间相互作用降低了羰基氧的电子密度。在烷基苯甲酸酯中,δ(17O)值可以用电感σI和空间位阻EsB取代基常数来描述。