| Abstract
| - The prediction of the entropy of fusion of organic compounds is studied. Rotational symmetry(σ) and flexibility (φ) have already been shown to contribute to the orientational andconformational entropy of fusion, respectively. Eccentricity (ε) and spirality (μ) are two newparameters that influence translational and configurational entropy. ε is defined as the ratio ofthe volume of a box around a rigid molecule to the cubed radius of a sphere containing the samemolecular van der Waals volume. μ is defined as the number of benzo[c]phenanthrene regionspresent in the molecule. This moiety results in repulsion and out of plane twisting to maximizethe distance between hydrogens. Enthalpy of melting, melting point, and geometrical data for117 compounds were gathered from the literature. The database consists of alkanes, polycyclicaromatic hydrocarbons, alkyl benzenes, and other alkyl aromatics. The addition of ε and μ to σand φ as predictors for the entropy of melting revealed a best fit melting point prediction linewith a slope close to unity and a coefficient of determination (R2) of 0.90. In addition, the averageabsolute error of melting point estimation was improved from 90 K to 43 K. Hence, the newlydefined ε and μ parameters offer significant improvement when combined with σ and φ in theprediction of the entropies of melting and, consequently, melting points of organic molecules.
|
