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Find the reactants of the following azo-coupling reaction: enter image description here

My solution would look like this:

enter image description here

My reason for the above answer

The amino Group is more activating than the nitro group and therefore the diazonium salt had to be on the left ring.

Is this correct? If not, what is the correct explanation?

Edit: To get to the azo-coupling product shown above I should use a high temperature, or? So, the reaction has to be thermodynamically controlled because the azo-group is localized on the 𝛽 carbon.

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    $\begingroup$ You have 2 amino groups in your starting material. Do you think there will be any problem of selectivity in the initial diazotisation? $\endgroup$ – Waylander Sep 21 at 20:02
  • $\begingroup$ If the diazonium salt would have been made on the naphthol molecule, this molecule would have had two amino groups. And the two amino groups would have produced two diazonium salts. This could not be used to obtain the wanted final diazo compound. $\endgroup$ – Maurice Sep 21 at 20:33
  • $\begingroup$ Well, no it's not good at all; in particular your rationale is completely backwards. $\endgroup$ – Mithoron Sep 21 at 22:02
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    $\begingroup$ In the future, please use a 2D chemical sketcher like ChemDoodle or ChemDraw online to draw structures: they're easier to use and produce better results $\endgroup$ – Aniruddha Deb Sep 22 at 2:56
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The comments summarized the reasons well: the diazotization reaction for the initial structure would produce a mixture of $\alpha$-azo and $\beta$-azo compounds, which would give a mixture of products. Also, diazonium salts couple with activated aromatic systems. The diazonium salt shown would not couple with nitrobenzene, which is highly deactivating and does not favour electrophilic aromatic substitution.

Also, having an electron withdrawing group on the diazonium salt favours the reaction. Thus, the correct solution would have the azo group on the smaller, less activated benzene ring rather than the larger, more activated naphthalene ring.

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  • $\begingroup$ But isn't $\alpha$-position on napthalene more "prone" to EAS than $\beta$? $\endgroup$ – Robin Singh Sep 22 at 3:28
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    $\begingroup$ @RobinSingh yes it is, and major product would be coupling opposite to phenol group. However, this looks more like a textbook problem of determining which ring would have the azo group initially, so I suggested the above. If you have to practically synthesize the first molecule, then there are a lot more reactions involved. $\endgroup$ – Aniruddha Deb Sep 22 at 5:51
  • $\begingroup$ It would probably be a good idea to summarize the comments at that point, and (or at least) link to them. There could be new comments later, or older ones deleted, it's better to have it all in one place. $\endgroup$ – Martin - マーチン Sep 22 at 12:36

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