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Dr. Russ- Org. Chem.

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Yes, there was a difference in my results between the solubilities of benzophenone in methyl alcohol and benzophenone in hexane. Benzophenone [essentially nonpolar (slightly polar due to the C=O bond)] was soluble in methyl alcohol, but only partially soluble in hexane. The reason for this is that methyl alcohol has an intermediate polarity, whereas hexane is nonpolar. FINISH. At this point I got confused... if benzophenone is basically nonpolar and hexane is nonpolar, then why wasn't benzophenone fully soluble in hexane and why was it fully soluble in methyl alcohol, rather than only partially?

  • Dr. Russ- Org. Chem. - ,

    The majority of materials that are soluble in a non-polar solvent like hexane are themselves non-polar, so I would expect that benzophenone which has no long chain part to be largely insoluble in hexane. It should however be soluble in say benzene or toluene.

    I am not surprised that benzophenone has some solubility in hexane. Similarly I am fairly sure that it also has a slight solubility in water.

    The ketone (C=O) will make the molecule slightly polar and thus soluble in polar solvents.

    The solubilities and polarities are not black and white. As you probably realise there is a scale of polarity between non-polar (hexane) and a polar molecule such as water. To add to the complication the structure of the molecule also has to be taken into account, such as can it hydrogen bond and does it have aromatic groups. The old adage of 'like dissolves like' is always a useful starting point.

    There is an added complication with ketones in alcohols in that the (C=O) can also react with the alcohol group to form C(OMe)2 (a ketal).

  • Dr. Russ- Org. Chem. - ,

    what is the solubility of benzophenone in toluene?

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