Electron-withdrawing constituents with pi electrons on the meta position of the benzene rings affect color significantly LESS than the same constitutnets on the ortho and para position. Why is this the case?
actually , groups with e-withdrawing destabilization of the conjugation py system in Azo dyes .
To address the second question about the effects of substituents on color, resonance is a requirement for color. Groups in the ortho and para positions on the ring will participate in resonance interactions unlike groups in the meta positions.
Hi,
indeed I fully agree with Tova N.W., to see what effects groups have on the system You could look up the Hammett values for meta and para positions (see the publication) this will also give You an idea how strong the difference may be. Secondly ortho position may be a bit tricky, because if the substituent is large enough a nodal twist may happen rendering the substituent isolated from the conjugation of the dye.
Cheers,
Kaspars
Article ChemInform Abstract: A Survey of Hammett Substituent Constan...
Hi
Azo compounds are colored due to the presence of double and triple bonds in addition to conjugation.
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