HYDROGEN-BOND BASICITY OF ESTERS, LACTONES AND CARBONATES

The thermodynamic hydrogen bond basicity scale pK(HB) (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 R(1)CO(2)R(2) the hydrogen bond basicity is decreased by bulky alkyl R(1) substituents (steric effect) but increased by branched and lengthened alkyl R(2) substituents (electronic effects). Quantitative structure-basicity relationships have been established in the XCO(2)Et (X varying from CF3 to NMe(2)) and XC(6)H(4)CO(2)Et (X varying from 4-NO2 to 4-NMe(2)) series. Vinylology strongly increases hydrogen bond basicity-Me(2)NCH=CHCO(2)Et is the most basic ester presently known. Cyclisation increases the hydrogen bond basicity of esters and carbonates.