USE OF MOLECULAR MODELING AS A TOOL TO EVALUATE THERMODYNAMIC STABILITY OF ALKYLATED POLYCYCLIC AROMATIC-HYDROCARBONS

Enthalpies of formation of alkylated naphthalenes calculated by group additivity, molecular mechanics, and MNDO methods resulted in similar thermodynamic stability classifications for a given set of di-, tri-, and tetramethyl isomers. The enthalpy data were related to the occurrence of individual alkylnaphthalenes in rock extracts and crude oils where the least stable isomers could not be detected. In contrast, the most stable ones were measured in variable proportions. Therefore, those data are potentially useful for predicting the presence or absence of individual isomers in natural samples. Changes in alkylnaphthalene distributions with increasing thermal maturity of the samples are also related to thermodynamic stabilities, as evidenced by an increase in abundance of the most stable relative to the least stable isomers.