ACD/Boiling Point

The boiling point of a pure substance is, in principle, a non-additive property. It has been observed experimentally that in homologous sets, the dependence of boiling point on the number of CH₂- groups obeys, approximately, the following non-linear function:

     (1)

where n_c is the number of CH₂- groups in the structure, bp is the observed boiling point, and a_i are empirically-determined constants. Note, however, that the additive algorithm cannot be applied to prediction of the Boiling Point.

We made a detailed comparison of the behavior of different macroscopic properties, such as the index of refraction (nd₂₀), density (d₂₀), and surface tension (γ), for different homologous sets, with respect to boiling point. We observed that all of these properties can be approximately described by Equation (1). These three properties are further related by different relationships between two out of four macroscopic properties (molar volume, molecular weight, molar refractivity, and the parachor):

via the following well-known functions:

         (2)

   (3)

       (4)

The noteworthy discovery, made by senior scientists at ACD/Labs, is that boiling point is a function of other additive molecular properties.