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Narrative
The intensity of the colors of complexes between benzene derivatives and tetracyanoethylene reveals the electron density on the aromatic rings.

Discussion
A 1% solution of tetracyanoethylene (TCNE) in dichloromethane is added to four test tubes containing benzene, toluene, m-xylene, and mesitylene respectively. The intensity of the color of the resulting p-complex increases with increasing electron density on the aromatic ring. A methyl group is electron donating and its effect is additive with mesitylene showing the highest electron density.