Dimerization of carboxylic acids:: Reliability of theoretical calculations and the effect of solvent

A large number of theoretical methods, ranging from classical calculations to high-level ab initio computations, have been used to study the dimerization of formic and acetic acids in the gas phase. Analysis of the results allows us to determine the range of accuracy expected for the different theoretical methods in the study of these types of interactions. The reasons for the errors occurring at high-level ab initio theory are discussed. Finally, the effect of the solvent on the dimerization of carboxylic acids is introduced using QM-SCRF, and MC-FEP methods. The reliability of both types of calculations is discussed. Results show that polar solvents play a key role in modulating the energetics of the dimerization of carboxylic acids. Dimerization free energies in the gas phase (1 atm) are found to be around -2 to -4 kcal/mol, values which are similar to those obtained in (1 M) chloroform solution. Dimerization free energies in (1 M) water are clearly positive (around 4-5 kcal/mol).