According to me tropolone has intramolecular H-bonding, so extent of H-bonding with water will decrease and thus, will be less soluble.

Tropone (Cyclohepta-2,4,6-trien-1-one):

enter image description here

Tropolone (2-hydroxytropone):

enter image description here

  • $\begingroup$ The fact that trololone can do strong hydrogen bonding suggests to me it will be more soluble in water. tropone can't do strong hydrogen bonding (no -OH group). So what are you comparing tropolone to? 3-hyroxytropone might be more soluble than the 2-hydroxy isomer, but on what basis can you compare solubility to something which isn't an isomer at all and doesn't have any hydrogen bonding? $\endgroup$
    – matt_black
    Jun 19 at 0:35
  • $\begingroup$ For the OSISIS property explorer, tropone yields a predicted value of cLogS of -1.39, tropolone of -1.32. Thus, for the trained model implemented (theory, 2k compounds, pH 7.5, 25 C). Of course, it is a model. $\endgroup$
    – Buttonwood
    Jun 20 at 19:54

The presence of internal hydrogen bonding does not automatically mean lower water solubility. The water solubility difference between fumaric and maleic acid provides a good example.

Maleic acid (the Z-isomer) is capable of an internal hydrogen bond between the two carboxylic acid functional groups.

enter image description here

Fumaric acid (the E-isomer) is not capable of internal hydrogen bonding. enter image description here

Maleic acid is about 100 times more soluble in water than fumaric acid.

  • Maleic acid: 480 g/L
  • Fumaric acid: 4.9 g/L

From these data, it is clear that the internal hydrogen bond is not an impediment to water solubility. Maleic acid is more soluble because it is more polar with the polar functional groups on the same side of the molecule. Fumaric acid is less soluble because it is less polar. The two polar functional groups are on opposite sides so the individual bond dipoles cancel.

This example may not extend to the comparison of tropone and tropolone, which are not isomers. Having reliable water solubility data for both compounds would provide useful information, but I was unable to find them.

  • $\begingroup$ Tropolone appears to have a solubility of about 5 g per L, but I couldn't find data for tropone, Thus, I made an analogy. Of course, data on the specific compounds will trump a generalization. $\endgroup$
    – Ben Norris
    Jun 16 at 20:22
  • 3
    $\begingroup$ So in the end, which is more soluble? $\endgroup$ Jun 17 at 3:23
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    $\begingroup$ I feel that this doesn't really answer the OP's question, it's more of an interesting tangent. $\endgroup$
    – S R Maiti
    Jun 17 at 9:53
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    $\begingroup$ @BenNorris “Maleic acid is ten times more soluble in water than fumaric acid. Maleic acid: 480 g/L Fumaric acid: 4.9 g/L“ Either the statement or the data has been given wrong by mistake, I suppose. Also, I agree with ShoubhikRMaiti that this really doesn’t answer the question OP has posed, though it is a important piece of information. $\endgroup$
    – Rishi
    Jun 17 at 12:05
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    $\begingroup$ @Buttonwood interestingly this post surfaced, which addresses your point: chemistry.stackexchange.com/questions/153155/… In retrospect I think my previous comment was not entirely correct. Need to think a little more about this. $\endgroup$
    – Buck Thorn
    Jun 20 at 15:36

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