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The thermodynamic hydrogen bond basicity scale pKHB(logarithm of the formation constant of 4-fluorophenol–base complexes in CCl4) has been determined for esters, lactones and carbonates, and correlated to a spectroscopic basicity scale. In the esters R1CO2R2 the hydrogen bond basicity is decreased by bulky alkyl R1 substituents (steric effect) but increased by branched and lengthened alkyl R2 substituents (electronic effects). Quantitative structure–basicity relationships have been established in the XCO2Et (X varying from CF3 to NMe2) and XC6H4CO2Et (X varying from 4-NO2 to 4-NMe2) series. Vinylology strongly increases hydrogen bond basicity—Me2NCHCHCO2Et is the most basic ester presently known. Cyclisation increases the hydrogen bond basicity of esters and carbonates.
Besseau et al. (Sat,) studied this question.