Estimation of the normal boiling point of organic compounds

A semiempirical model has been developed for the estimation of the normal boiling points of organic compounds. The normal boiling point is calculated as the ratio of the enthalpy of boiling to the entropy of boiling. Both these values are estimated independently using a combination of additive group contribution and nonadditive molecular descriptors. A group contribution model is proposed for the estimation of the enthalpy of boiling, based on the experimental data for 1322 structurally diverse organic compounds. The average absolute error associated with this estimation is 0.83 kJ/mol. A semiempirical model has been developed for the estimation of the entropy of boiling using experimental entropy data for the entire set. This model is a modification of Trouton's rule and takes into account the effect of hydrogen bonding and molecular flexibility. The average absolute error associated with this estimation is 4.7 J/(K mol). The average absolute error associated with the estimation of the normal boiling point, calculated as a ratio of the enthalpy of boiling to the entropy of boiling, for the entire data set is 9.3 K (2.3%). A good correlation is observed between the estimated and the experimental boiling points with an r(2) of 0.98. This model is easy to use, accurate, and applicable to a wide variety of organic compounds.