# How to determine the order of elution in silica gel column chromatography?

Benzofuranoids ustusoranes A (1), B (2), and E (3) were isolated from Aspergillus ustus 094102. If these compounds were separated by column chromatography on silica gel, what would be the elution order? (top — comes off the column first, bottom — comes off last).

As I get it, column chromatography is like TLC where in a silica gel the nonpolar compound comes out first.

• The comparison with TLC is valid, and your judging of polarity, based on the interaction of the $\ce{OH}$ groups with the silica sounds good. So, yes, I would come to the same conclusion. If you would perform the separation in the lab, you would nevertheless keep all three fractions and determine the structures by independent methods (NMR). – Klaus-Dieter Warzecha Mar 3 '17 at 9:11

• @orthocresol Diffusion in a column can go $x$ and $y$, elution is $-z$. In a TLC, elution is also $z$, but diffusion can only happen in $x$ direction. – Jan Mar 3 '17 at 23:27
• I always thought 2D TLC referred to the thing where you develop along $z$ direction, then rotate it by $90^\circ$, stick it in a different solvent system, and develop along $x$ direction. – orthocresol Mar 3 '17 at 23:33