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Is hexan-1-ol or cyclohexanol more soluble in water? The answer is supposedly cyclohexanol. However, I found a statement in a book:

Isomeric alcohols have solubilities in the order: primary alcohol > secondary alcohol > tertiary alcohol, due to decrease in polar character.

By this statement, I guessed the answer to be 1-hexanol, as it is a primary alcohol whereas cyclohexanol is a secondary alcohol. What mistake have I done?

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    $\begingroup$ Hexanol H13C6OH and cyclohexanol H11C6OH are not isomeric. $\endgroup$
    – Karl
    Commented Jan 3, 2017 at 18:34
  • $\begingroup$ When comparing solubilities, it is helpful to see actual numbers: 1-hexanol is soluble 5.9 g/L; cyclohexanol is soluble 36 g/L in water at 20C. Big difference, but not overwhelming. The solubilities are still relatively small, far from miscibility. $\endgroup$
    – James Gaidis
    Commented Aug 12, 2022 at 14:31

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In general, is very difficult to predict solvation some experimental models are used such as Abraham solvation equation. I suppose that the mistake you have done is linked to the fact that you haven't considered one of the most important factors: the molecule structure.

In this case, you are comparing a cyclic compound with a linear one, if you could have a look at the potential surface of the two molecules you will see something like this:enter image description here

What makes the alcohol soluble is the hydrophilic hydroxyl group while the lipophilic chain is not. The ratio between hydrophilic and lipophilic areas is greater in cyclohexanol compared to 1-hexanol.

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First I'd have to agree with Karl's comment that 1-hexanol ($\ce{C6H13(OH)}$) and cyclohexanol ($\ce{C6H11(OH)}$) are not isomeric. So when you're compare apples to oranges you can come to unfounded conclusions.

The gist in this case is however dependent on the "polar surface area" to the total surface area of the molecule. The molecules will have about the same polar surface area, but the cyclohexanol will have less total surface area. Thus cyclohexanol dissolves better in water.

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