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A nitro group is a strong deactivator whereas a halogen is a weak deactivator. The directing effects of these groups oppose each other: Nitro is meta directing whereas halogens are ortho/para directing. It is said that the strongest activator determines the directing effects in a disubstituted benzene ring. In a ring with no activators, such as one containing a halogen and a nitro group, is the weakest deactivator considered the "strongest activator", so that in the example I have just given the halogen would control the directing effects and said ring would be ortho/para directed?

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  • $\begingroup$ How about an example of a "nitro halo" compound? $\endgroup$ – user55119 Oct 28 at 23:45
  • $\begingroup$ @user55119 Could one not nitrate phenyl chloride? $\endgroup$ – David Reed Oct 28 at 23:48
  • $\begingroup$ o, m, or p-chloronitrobenzene? $\endgroup$ – user55119 Oct 29 at 1:14
  • $\begingroup$ @user55119 This is not a homework question. It is frustrating that you would make that assumption. I was giving a concrete example to indicate an instance in which my question would have relevance. I was far more interested in understanding the rule at issue than the answer to the specific question. All persons who voted to put this question on hold have committed a cardinal sin of science: Never make unwarranted assumptions. $\endgroup$ – David Reed Oct 30 at 2:36
  • $\begingroup$ You may want to look at this: chemistry.stackexchange.com/questions/91636/… $\endgroup$ – user55119 Oct 30 at 18:54
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I think you are reaching the limitations of directing group rules. These rules are not perfect and can often break.

In this example, chloride and nitro meta to each other, the group should add meta to the nitro group because the nitro group has a much more significant effect on the electronics of the molecule.

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  • $\begingroup$ This was my initial impression but the book has several examples in which a weak activator trumps a nitro group (i.e. the ring will be ortho/para directed) $\endgroup$ – David Reed Oct 28 at 23:59
  • $\begingroup$ @David Reed: Why shouldn't a weak activator take precedent over a nitro group? Still looking for a concrete example from your book. $\endgroup$ – user55119 Oct 30 at 17:22
  • $\begingroup$ @user55119 A concrete example from book: Regarding direction of o-isopropylnitrobenzene: "In this case, a weak activator is competing with a strong deactivator for directing effects. Recall the more powerful activator controls the directing effects, so the isopropyl group determines the outcome in this case. The isopropyl group is ortho/para directing, so we must consider the positions that are ortho and para to the isopropyl group". My question is if a weak activator controls directing effects against a strong deactivator (because the strongest activating group controls), will a weak... $\endgroup$ – David Reed Oct 30 at 20:29
  • $\begingroup$ @user55119 ..deactivator similarly control directing effects against a strong deactivator, as one could reason that a weak deactivator is "more activating" than a strong deactivator, and hence would be the "strongest activator" $\endgroup$ – David Reed Oct 30 at 20:30
  • $\begingroup$ @David Reed: I can't speak to your logic but CH3O in anisole is a stronger o,p-activator than Cl in chlorobenzene because a positive charge is more readily sustained on oxygen than on chlorine. A Friedel-Crafts (FC) acylation of a mixture of the 2 aromatics with an acyl halide as the limiting reagent will give more of the anisole-derived product. The FC reaction of either anisole or chlorobenzene can be conducted in nitrobenzene as the solvent!! $\endgroup$ – user55119 Oct 30 at 22:38

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