Would ethyl acetate/hexane be considered nonpolar or polar overall? I know that the ethyl acetate is polar and the hexane is nonpolar. I am trying to understand what if polar or nonpolar analgesics would travel further in TLC. I know that if ethyl acetate/hexane is polar than a more polar one will travel further, and if it is nonpolar then nonpolar will travel further.

I was looking here and I see that caffeine is the most polar (out of aspirin and acetaminophen) and traveled the least distance (lowest $R_\mathrm{f}$) in my experiment. I thought that ethyl acetate/hexane was polar so I would have thought caffeine would be the least polar since it traveled the shortest.

So am I wrong that ethyl acetate/hexane is polar or are they wrong that caffeine is the most polar?

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    $\begingroup$ For normal phase TLC the more polar compound always travels slower. $\endgroup$
    – orthocresol
    Feb 28 '17 at 18:45
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    $\begingroup$ The link seems to have disappeared. Ethyl acetate is polar. Hexane is non-polar. So by using a mixture of the two you can get solutions of varying polarity. Adjusting polarity that way is easier than trying to find 10 different solvents of varying polarity. $\endgroup$
    – MaxW
    Feb 28 '17 at 18:46
  • $\begingroup$ I used a silica gel for the plate... Does that make it normal phase TLC? $\endgroup$
    – Math4Life
    Feb 28 '17 at 18:48
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    $\begingroup$ Basically using a polar stationary phase (which a silica plate is) makes it normal phase TLC. $\endgroup$
    – MaxW
    Feb 28 '17 at 19:12

Never have I seen a normal phase (i.e. silica gel or alox) TLC where a more polar compounds travels further than a less polar compound — and I have used some extremely (considering normal phase TLC) polar eluents in the past.

The top-running compounds are always the least polar and the slowest are always the most polar in normal phase TLC.

  • $\begingroup$ How about using aniline vs glacial acetic acid to develop amines versus carboxylic acids? // Grand dogmatic statements in chemistry always bother me. It seems that there is always some weird exception. // I do get that you're talking about "normal expectations"... $\endgroup$
    – MaxW
    Feb 28 '17 at 22:35
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    $\begingroup$ @MaxW Haha~, but then we have the anion in one case and the neutral molecule in another. I consider those different species for the sake of the argument. $\endgroup$
    – Jan
    Feb 28 '17 at 22:42

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