Chapter 10 - Carboxylic Acids

Abstract

The type of carboxylic acid of form RCO2H had to be identified before its approximate pKa value could be calculated from vC=O and the out-of-phase (C=O)2, vop(C=O)2, frequencies recorded in CCl4 solution. The vC=O and vop(C=O)2 frequencies recorded in CCl4 solution have been reported to correlate in a linear manner with pKa values. It has been reported that vop(C=O)2 band intensities for aromatic carboxylic acids are higher than those for aliphatic carboxylic acids. In the vapor-phase at temperatures above 150°C, carboxylic acids exist only in the monomeric state. At lower temperature, both the monomer and dimer carboxylic acid can exist in equilibrium. With increase in temperature, the equilibrium shifts toward the monomeric species. In CC14 solution, the 4-nitro analog would have the most acidic OH proton and the most basic C–O oxygen atoms. Therefore, a complex such as (F) would cause the C=O bond to be strengthened.