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I understand that relative to p-nitrophenol, o-nitrophenol would be more steam volatile (as p-nitrophenol can form intermolecular hydrogen bonds), but my question lies in the fact that its volatile nature is often attributed to its ability to form intramolecular H bonds. How does this contribute to steam volatility?

Also, assuming that it is true that steam volatility is a result of intramolecular H bonding, then picric acid would be more steam volatile than p-nitrophenol, which is not true (as it has a higher boiling point). Doesn't this result directly contradict the assumption?

Just a quick note, my question doesn't relate to the actual process of steam distillation (was closed b/c it was similar to something related - I'm just curious about why picric acid is not more steam volatile than p-nitrophenol.)

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  • $\begingroup$ @Mithoron it doesn't actually, my doubt is regarding the effect of H bonding on steam volatility, not the process itself. thanks though! :) $\endgroup$
    – rania h
    Commented Feb 25 at 13:46
  • $\begingroup$ Intramolecular H-bonding decreases availability for intermolecular H-bonding and general polar bond interactions, making the molecule effectively less polar and more volatile. $\endgroup$
    – Poutnik
    Commented Feb 25 at 14:14
  • $\begingroup$ @Poutnik That makes sense - thanks! I was curious as to how that'd explain the higher boiling point of picric acid when compared to p-nitrophenol? I'd imagine picric acid to undergo intramolecular H bonding and thus, have a lower b.p. and greater volatility. $\endgroup$
    – rania h
    Commented Feb 25 at 17:24
  • $\begingroup$ Picric acid has a much large molecular weight, 229 vs 139 g/mol. That's enough to justify the difference, but that's just one factor. The example of intramolecular H bonding illustrates the potential importance of this effect but it is only another of many factors. $\endgroup$
    – Buck Thorn ♦
    Commented Feb 25 at 18:49
  • $\begingroup$ I think it kinda does, you just didn't see it. H-bonding is like last thing that's important, you need to know basics first - why it does anything, which still is not that much. $\endgroup$
    – Mithoron
    Commented Feb 25 at 23:21

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