Comparison of calculated equilibrium mixtures of alkylnaphthalenes and alkylphenanthrenes with experimental and sedimentary data; the importance of entropy calculations

Evaluation of the relative stabilities of tetramethylnaphthalenes and dimethylphenanthrenes by means of molecular mechanics calculations allows one to predict the equilibrium mixture compositions for these groups of compounds. These equilibrium compositions have been calculated at various temperatures with and without taking into account the entropy of the compounds. Comparison with experimental observations, and sedimentary data, showed that when entropy is taken into account in the calculations, agreement between the experimental and sedimentary data is much improved. A distinct temperature dependence of the equilibrium composition is predicted for the tetramethylnaphthalenes, indicating the potential of this group of compounds for burial temperature evaluations.