Trouton's Rule vs. Boiling Point (Textbook 4F.15-16)

[Zach C-2J]

Spotted these two questions and was wondering about the difference mentioned towards the end:

https://imgur.com/a/v5Amo4R

Actual of dimethyl ether: -24 °C
Actual of methylamine: -6.3 °C

[Chem_Mod]

The difference comes from the fact that Trouton's Rule is an approximation. Trouton's Rule says that the entropy of vaporization of many organic liquids is about 85 J/(mol*K). We can then use this value to calculate a boiling point using the equation T(bp) = (delta H vap)/(delta S vap). This value is a good estimate of the boiling point, but it is still an estimate and there is some difference because we approximated the entropy of vaporization of the organic liquids.