Master Curve and Troutons Rule

It has been pointed out that Trouton s rule is not a strict law, but a remarkable good approximation [13]. The rule works best for nonpolar, quasi-spherical molecules. 

If the plot of the reduced vapor pressure against the reciprocal reduced temperature fits a master curve, it does not mean that the rule of Trouton is valid. To meet the rule of Trouton, also the rule of Hildebrand must be valid. In this case, all the boiling points will be found at r /r = Tc/Tb = 3/2 = 1.5. On the other hand, if the corresponding states are sound, then all substances should have a common critical pressure, because In Pb/Pc = C in this case (since Pb = 1 atm). 

We can see this fact also of the coexistence curve in the double logarithmic plot of the reduced pressure against the reduced temperature. The slope of this plot becomes, in the limiting case, that of an ideal gas phase, and the volume of the liquid 

Shinoda, K. Entropy of vaporization at the boiling point. J. Chem. Phys. 78,4784 (1983) 

Wisniak, J. Frederick Thomas Trouton The man, the rule, and the ratio. Chem. Educat. 6(1), 55-61 (2001) 

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