TLC: which compound travels farthest?
A mixture of toluene, benzyl alcohol, and benzoic acid is run on a silica gel TLC plate with a nonpolar solvent. Which compound has the highest Rf?
Answer A: explanation for every choice
A
Correct. Silica is polar and holds polar compounds back. The least polar compound moves farthest with the nonpolar solvent.
B
The alcohol's hydroxyl group hydrogen-bonds with silica and slows it down.
C
Carboxylic acids bind silica most strongly and have the lowest Rf.
D
The compounds differ in polarity, which is what TLC separates.
TakeawayNormal-phase TLC: less polar → higher Rf.
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Reviewed 2026-11-05 by a medical student. Spot an error? Report it with question ID cp144.