Tert-butyl alcohol seems unusual among alcohols in that its melting point is high (25°C) while its boiling point is also still low (82°C). I am looking for more materials with phase-unstable liquid regions like this so I'm curious what makes the liquid phase so unstable relative to the solid and gas phases?
Do the methyl groups align and act like alkanes to stabilize the solid but the molecule is still small enough to have a low boiling point?
To my larger point, any advice on characteristics of materials that exhibit low liquid phase stability?
Answer
Highly symmetric molecules tightly fit into crystal lattices, give high melting points for their composition. Their small surface areas minimize London dispersion forces and van der Walls forces, giving high volatility. They tend to sublime. Compare mp and bp data for cyclohexane and benzene versus their perfluorinated derivatives. Less exotic: n-octane, iso-octane, 2,2,4-trimethylpentane, 2,2,3,3-tetramethylbutane, and cubane.
http://en.wikipedia.org/wiki/Neopentane
n-Pentane and isopentane versus neopentane.
Chromium, molybdenum, and tungsetn metal versus their respective hexacarbonyls. $\ce{-SiMe3}$ and $\ce{-CF3}$ plus symmetry confer remarkable volatility. $\ce{I(CF3)7}$ melts and boils around 0 C. That is molecular weight 609.95 - and it has no static molecular structure (Bartell mechanism).
http://www.patentgenius.com/patent/3992424.html
US Patent 3992424
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