MONTE-CARLO SIMULATIONS OF LIQUID ACETIC-ACID AND METHYL ACETATE WITH THE OPLS POTENTIAL FUNCTIONS

Intermolecular potential functions have been developed for carboxylic acids and esters in the OPLS format by performing Monte Carlo simulations for liquid acetic acid at 25 and 100-degrees-C and for liquid methyl acetate at 25-degrees-C. The potential function parameters were chosen such that experimental thermodynamic and physical properties were reproduced within ca. 1-4%. In liquid acetic acid, the monomers are computed to be in an average of nearly two hydrogen bonds, there is a negligible occurrence of non-hydrogen-bonded monomers, and 7-16% of the monomers are in cyclic dimers. Some experimental studies have been interpreted to indicate that the liquid consists mostly of cyclic dimers, while others suggest that it is a mixture of linear and cyclic polymers, linear and cyclic dimers, and very few free monomers. In the current study it is found that liquid acetic acid consists mainly of hydrogen-bonded chains. Liquid methyl acetate is relatively structureless.