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Benzophenone in Hexane vs. Methyl Alcohol

weanprednisone

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Jun 6, 2015
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    Question: Is benzophenone more soluble in MetOH or Hexane?
    Answer: Benzophenone dissolves faster in MetOH than in Hexane.

    Benzophenone is a ketone, making it polar, but majorly nonpolar with two phenyl rings.
    If we would put these in terms of fractions, I would say that this molecule is 3/4 nonpolar, and 1/4 polar.

    So this molecule being majorly nonpolar, why would it be more soluble in MetOH than in Hexane?
    Is it because the -OH on MetOH can perform H-bonding with the keto- group?
    But wouldn't the dispersion forces be more dominant with the 2 phenyl rings?
     

    GypsyHummus

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      Question: Is benzophenone more soluble in MetOH or Hexane?
      Answer: Benzophenone dissolves faster in MetOH than in Hexane.

      Benzophenone is a ketone, making it polar, but majorly nonpolar with two phenyl rings.
      If we would put these in terms of fractions, I would say that this molecule is 3/4 nonpolar, and 1/4 polar.

      So this molecule being majorly nonpolar, why would it be more soluble in MetOH than in Hexane?
      Is it because the -OH on MetOH can perform H-bonding with the keto- group?
      But wouldn't the dispersion forces be more dominant with the 2 phenyl rings?

      Hexane is just 6 carbons in a chain with no polarity to speak of. You already mentioned that Benzophenone is a ketone, and Os on the benzo make it a somewhat polar molecule. MethOH is an extremely polar molecule, therefore, the slightly polar ketone would love to interact with the extremely polar molecule as opposed to the party pooper non polar one.
       

      Necr0sis713

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        What you have to consider are the resonance structures of the benzophenone. The molecule isn't just a ketone; the oxygen is essentially withdrawing electrons and the phenyl rings are stabilizing the carbonyl carbon (that have partially positive character). So the molecule is kind of a hybrid with a charged oxygen. A charged oxygen is gonna have a good time with the hydrogen of the alcohol.

        Just think of the oxygen sucking up all the electron density from the carbon, and the electrons in the rings are spinning and each helping to stabilize that carbon by "filling in the gap" with their pi bonds. They're like spinning wheels inserting pi bonds into that positive carbon zone, while the oxygen is an electron sink.
         
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        weanprednisone

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        Jun 6, 2015
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          Hexane is just 6 carbons in a chain with no polarity to speak of. You already mentioned that Benzophenone is a ketone, and Os on the benzo make it a somewhat polar molecule. MethOH is an extremely polar molecule, therefore, the slightly polar ketone would love to interact with the extremely polar molecule as opposed to the party pooper non polar one.
          Thanks, I understand that. But considering the nonpolarity/dispersion forces in the two phenyl rings, that should intrinsically attract hexane (dispersion forces).

          For anyone wondering, the reason why benzophenone is more soluble in MetOH is due to the size of the solvent. MetOH=32 g/mol and Hexane=84 g/mol. MetOH is able to surround benzophenone more compared to Hexane, since its so big. Therefore with more area contact with MetOH, its able to interact more.
          So I guess IMF/polarity is not the way to think about it. Rather, its the solvent size :/
           
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