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

Discussion
A 1% solution of tetracyanoethylene (TCNE) in dichloromethane is added to each of four test tubes containing nitrobenzene, chlorobenzene, benzene, and anisole respectively. TCNE forms colored p-complexes with aromatic rings and the intensity of the color increasing with increasing electron density of the ring. The nitro- and chloro- groups are both electron withdrawing. Nitrobenzene gives no added color, and chlorobenzene gives a pale yellow color with TCNE. The methoxy group is strongly electron donating and gives a purple color with TCNE.