METHODS TO PREDICT THE VAPORIZATION ENTHALPIES AT THE NORMAL BOILING TEMPERATURE OF PURE COMPOUNDS REVISITED

A previous method for predicting the vaporization enthalpies of pure compounds at the normal boiling temperature (T-b) based on (T-b) and the molecular weight (M) as input parameters is re-examined. A remarkable improvement is obtained by introducing new rules to evaluate fictitious molecular weights for halogens and phosphorus and by recalculating the empirical parameters of the relationship by regressing new and more reliable experimental data for Delta H-b. Further, a new family of relationships for Delta H-b is derived which embodies an empirical parameter, W-p, whose value is related to the polar character of a molecule. This parameter is, in turn, a function of T-b and M only. A comparison is made with some well-known literature relationships based on T-b and the critical parameters in their ability to calculate the vaporization enthalpies of 110 pure compounds representative of polar, non-polar and strongly associated molecules.