Resumo

DUCHOWICZ, P.R; CASTRO, E.A.; FERNANDEZ, F.M.  e  PANKRATOV, A.N.. QSPR Evaluation of thermodynamic properties of acyclic and aromatic compounds. An. Asoc. Quím. Argent. [online]. 2006, vol.94, n.4-6, pp.31-45. ISSN 0365-0375.

Although parametrized Semiempirical Molecular Orbital Methods were especially designed to obtain enthalpies of formation and other related thermodynamical parameters, in some situations the predictions cannot be compared to the experimental results simply because they present serious drawbacks.Therefore, there is room to apply a wide variety of predictive methods for estimating thermodynamical properties, such as the well-known Group Contribution Methods and the Quantitative Structure-Property Relationships. A QSPR study of 163 enthalpies of formation, 37 Gibbs free energy changes, and 40 standard entropies of elements is established for a representative set of acyclic and aromatic compounds, on the basis of fundamental concepts on molecular structure such as the count of atoms and types of chemical bonds. A recent method discovered in our group called the Replacement Method is employed here to find the best models in a pool containing 33 descriptors. An 8 parameters-model was able to correlate the heats of formation with atoms and bond types (R=0.9553, R_l-25%-o=0.8200) but with great dispersion ( S=19.173 Kcal/mol ). For the case of standard entropies (R=0.9813, R _l-20%-o=0.8659) and for free energies (R=0.9869, R _l-20%-o=0.9000) the models obtained perform poorer than those calculated with Semiempirical Methods.