This question that I recently encountered asked what the most suitable substrate for the Ullmann reaction would be. The answer given is (b) but I think it has to be (d) as the nitro group acts as EWG and thus facilitates the reaction.

However I do not know the mechanism and thus am not sure if (d) is indeed the correct answer.

Any reason why the answer might be (b) and not (d)?

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I think that the answer given in your textbook is wrong as they are trying to conduct ULLMANN reaction on a chloride a strong EWD needs to be present at the ortho/para positions for the reaction to be feasible.

There Are generally 2 Mechanisms Proposed for the reaction :

  1. Free Radical Mechanism
  2. Ionic Mechanism

The Copper Metal (used as catalyst) Generate a Aryl Radical By transferring a electron, and then 2 Aryl Radical combine to form the final product. FREE RADICAL MECHANISM

Acording to this a Organometalic intermideate of Aryl copper halide is fromed. The copper is added to the Aryl halide by Oxidative addition. then a electron is transfered to the intermidiate to for a organocuppric radical which again perform the oxidative addition on another aryl halide which result in formation of a biaryl copper complex which in turn undergo reductive elimination and make the final product. enter image description here

You can easily see that we need a EWG to make the Reagent more reactive thus making the reaction feasible thus your answer must be either wrong or you might have checked it wrong. nevethless I also find this paper affirming mine and your belief.


  1. https://link.springer.com/article/10.1007/s40828-016-0036-2
  2. www.name-reaction.com/ullmann-reaction
  • 1
    $\begingroup$ I may be wrong,but isn't a free radical destabilized by an EWG,considering that it is an electron deficient species? So why would EWGs facilitate the reaction? $\endgroup$ Feb 11 '19 at 5:39
  • $\begingroup$ @YUSUFHASAN no I don't think so as the free readical is formed on a sp2 carbon $\endgroup$
    – Advil Sell
    Feb 11 '19 at 6:21
  • $\begingroup$ @AdvilSell See this It clearly states that a free radical is an electron deficit species,and it's stability is similar to a carbocation $\endgroup$ Feb 11 '19 at 7:02
  • $\begingroup$ So even if -M effect is not operative then also -I effect surely is via the sigma bonds $\endgroup$ Feb 11 '19 at 7:12
  • $\begingroup$ @YUSUFHASAN yes i was mad when i wrote it , it has been a bad day till now please accept my apology i have edited the answer the EWG make the intermidate more reactive making the reaction faster as its a radical intermideate reaction the reaction is kinetically controlled $\endgroup$
    – Advil Sell
    Feb 11 '19 at 7:14

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