Enthalpies of formation of methyl substituted naphthalenes

In this work, the enthalpies of formation for the homologous series of methyl substituted naphthalene isomers were calculated using the AM1, PM3, B3PW91, and G3MP2 methods. This work was done primarily to address the lack of data available for many of these compounds and to find the most cost-effective method to calculate the enthalpy of formation. In addition, we explored the development of a group-additivity model as a fast method to calculate the enthalpy of formation. Using this model, two sets of interaction parameters were derived. One set from the G3MP2 results and the other from the B3PW91 results. These parameters differ by an average of 2.3 kJ mol^-1, implying that the simpler B3PW91 calculations may be used to develop a group-additivity model. The model using the G3MP2 derived parameters deviate from the experimental values with a RMS of 3.0 kJ mol^-1. Using the B3PW91 parameters, the model has an RMS of 9.1 kJ mol^-1.