Hydrogen-bond basicity of esters, lactones and carbonates

Abstract

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 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.