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 occurre nce of individual alkylnaphthalenes in rock extracts and crude oils wh ere the least stable isomers could not be detected. In contrast, the m ost stable ones were measured in variable proportions. Therefore, thos e data are potentially useful for predicting the presence or absence o f individual isomers in natural samples. Changes in alkylnaphthalene d istributions with increasing thermal maturity of the samples are also related to thermodynamic stabilities, as evidenced by an increase in a bundance of the most stable relative to the least stable isomers.