Thermochimica Acta, Vol.290, No.1, 55-64, 1997
Enthalpies of Sublimation and Formation of Polycyclic Aromatic-Hydrocarbons (PAHs) Derived from Comparative Molecular-Field Analysis (CoMFA) - Application of Moment of Inertia for Molecular Alignment
A Quantitative Structure-Property Relationship (QSPR) is developed from the 3D-QSAR method CoMFA to estimate the sublimation enthalpy (Delta(sub)H(m)(0) (298.15 K)) and formation enthalpy (Delta(f)H(m)(0) (298.15 K)) of a series of polycyclic aromatic hydrocarbons (PAHs). A unique feature of the present analysis is the application of moment of inertia as the basis for aligning the PAH molecules in the data set, which included nonplanar structures. Partial least-squares (PLS) regression with cross validation was employed to correlate each of the two thermodynamic properties with the steric and electrostatic fields surrounding each PAH molecule. The resulting CoMFA model for Delta(sub)H(m)(0) (298.15 K) yielded r(2) values of 0.817 (cross-validated) and 0.948 (conventional) using a training set of 30 PAHs, while that for Delta(f)H(m)(0) (298.15 K) yielded r(2) values of 0.617 (cross-validated) and 0.998 (conventional) using a training set of 16 PAHs. CoMFA-predicted values of Delta(sub)H(m)(0) (298.15 K) for a test set of 5 PAHs agreed within an average 5% of the corresponding experimental values. Contributions to the CoMFA models from the 3D steric and electrostatic fields were 93% steric and 7% electrostatic for Delta(sub)H(m)(0) (298.15 K) and 66% steric and 34% electrostatic for Delta(f)H(m)(0) (298.15 K), reflecting the strong correlation between steric bulk as encoded in the CoMFA steric fields and both of these thermodynamic properties. The present CoMFA models were used to predict the Delta(sub)H(m)(0) (298.15 K) and Delta(sub)H(m)(0) (298.15 K) values of several PAHs for which the corresponding experimental values are unavailable.