How to compare the melting points of the above isomers? I know that melting point depends upon the packing of the molecule, more efficient the packing, higher is the melting point. Symmetry in a compound also increases it's melting point. But all the above compounds have symmetry in them and I can't figure out how to compare their melting points.

  • $\begingroup$ I and III have 2 planes and 1 axis. II has 1 plane and 1 axis $\endgroup$ – Maurice Feb 2 at 20:16
  • $\begingroup$ @Maurice So what should we conclude from that? $\endgroup$ – Light Yagami Feb 3 at 3:17
  • $\begingroup$ Based on «the better (i.e., more regular) packing, the higher the melting point», my speculation the melting points increase along III -> I -> II. This extrapolates*) from the packing of atoms in metals. While none of the three molecular structures is a sphere, in my perception, compound II is the most sphere like of the three. And neither one of the three has strong hydrogen bond donors and acceptors to increase the strength of the intermolecular attractive interactions (except H-B). *) Of course, extrapolations always come with the danger to potentially lead to a wrong conclusion. $\endgroup$ – Buttonwood Feb 3 at 12:56
  • $\begingroup$ @Buttonwood: Thank you for your comment. But how are you perceiving the 2nd compound as more sphere like? Can the melting point data be checked from somewhere? $\endgroup$ – Light Yagami Feb 3 at 13:04
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    $\begingroup$ @Buttonwood I think you should read about pi-stacking $\endgroup$ – Mithoron Feb 3 at 15:16

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