DIMERIZATION OF CARBOXYLIC-ACIDS - RELIABILITY OF THEORETICAL CALCULATIONS AND THE EFFECT OF SOLVENT

A large number of theoretical methods, ranging from classical calculat ions 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 inte ractions. The reasons for the errors occurring at high-level ab initio theory are discussed. Finally, the effect of the solvent on the dimer ization of carboxylic acids is introduced using QM-SCRF, and MC-FEP me thods. The reliability of both types of calculations is discussed. Res ults show that polar solvents play a key role in modulating the energe tics of the dimerization of carboxylic acids. Dimerization free energi es 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 solutio n. Dimerization free energies in (1 M) water are clearly positive (aro und 4-5 kcal/mol).