5

What makes the first 3 alkanes decrease in melting point (m.p.) while after that they rise?

$$ \begin{array}{lr} \hline \text{Alkane} & \text{m.p.}/\pu{°C} \\ \hline \text{Methane} & -182 \\ \text{Ethane} & -183 \\ \text{Propane} & -188 \\ \text{Butane} & -138 \\ \text{Pentane} & -130 \\ \text{Hexane} & -95 \\ \text{Heptane} & -91 \\ \text{Octane} & -57 \\ \hline \end{array} $$

Harry Tong
  • 209
  • 2
  • 4
  • 2
    It is packing . After the first terms then molecular surface takes the leading role. Perhaps someone will articulate in a more complete form but the juice is this. – Alchimista Mar 10 '18 at 10:18
  • 1
    https://chemistry.stackexchange.com/questions/89689/for-two-compounds-that-are-symmetrical-why-does-the-more-compact-one-have-a-hig https://chemistry.stackexchange.com/questions/71417/why-alkanes-containing-even-number-of-carbons-can-be-packed-more-efficiently-tha – Mithoron Mar 10 '18 at 15:20

0 Answers0