mysticmuse
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Reactivity of aromatic cycles
I usually understand what is more reactive when there is only one substituent, ex: phenol, chlorobenzene but I'm stuck when I'm asked to find what is
more reactive when there are 2 substituants.
This is the the question: Place in order of reactivity the following compounds - acetanilide, benzene, chlorobenzene, 4-nitrophenol, phenol,
4-chlorophenol.
This is my guess: phenol>4-chlorophenol>4-nitrophenol>acetanilide>benzene>chlorobenzene
The problem with my reasoning is that I only considered the second substituants 4-nitrophenol and 4-chlorophenol when I compared them to eachother,
not with the other compounds. Can someone please explain me how to find the correct order? Thanks.
[Edited on 26-10-2010 by mysticmuse]
[Edited on 26-10-2010 by mysticmuse]
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ScienceSquirrel
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Personally I would go for;
phenol>acetanilide>4-chlorophenol>4-nitrophenol>benzene>chlorobenzene
I reckon the acetanilide would be less reactive than phenol but more reactive than the substituted phenols.
To be honest these things can depend on the electrophile and the reaction conditions, etc.
Have a look at this, I think it shows that my order is correct;
http://www.uni-regensburg.de/Fakultaeten/nat_Fak_IV/Organisc...
[Edited on 26-10-2010 by ScienceSquirrel]
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Ebao-lu
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| Quote: | I reckon the acetanilide would be less reactive than phenol but more reactive than the substituted phenols.
To be honest these things can depend on the electrophile and the reaction conditions, etc. |
on the one hand, it is right but in the other hand nitration of paracetamol leads to http://www.sciencemadness.org/talk/viewthread.php?tid=9722
I guess that depends on acidity - in basic solution phenol becomes a much more reactive phenolate, in neutral phenolate can also form in equilibrium
and in acidic its concentration is less. Or there is some other reason of such paracetamol nitration product formation. Anyway, i think you
mysticmouse can answer acetanilide is more active because it was not mentioned about base presence, and about neutral pH i'm not sure. If teacher is
not satisfied you can provide a refference at least. Or you can study what other reactions with paracetamol are resulting in like chlorination,
bromination etc that are made in neutral pH
[Edited on 26-10-2010 by Ebao-lu]
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Nicodem
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To qualitatively determine the aromatic nucleophilicity (reactivity of the aromatic systems toward electrophiles) is not easy as one needs to evaluate
all kind of electronic effects and resonance systems and subsystems. It is similarly difficult to predict the regioselectivity of the electrophilic
aromatic substitution (EAS). To illustrate how apparently simple substrates give unusual regioselectivity, check this recent thread. Besides, with protic or basic functional groups, the reaction media acidity/basicity has a huge influence on reactivity
(as mentioned above for phenols, but the same is also true for anilines, benzoic acids, benzyl amines, etc., in extreme cases this phenomenon
influences the reactivity of substrates such as anisols or even nitrobenzenes). Sterics also have an important influence on the reactivity, just as
they also influence regioselectivity. An additional problem in regioselectivity prediction is a common complication in the EAS, which is the side
reactions resulting from ipso attacks of the electrophile. Reactivity and regioselectivity in EAS are highly interconnected and can not be evaluated
separately.
BTW, homework requests and pedagogic stuff go to Beginnings section where I'm moving this.
[Edited on 26/10/2010 by Nicodem]
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Nicodem
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Thread Moved
26-10-2010 at 07:38 |
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