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Topic: Why halide are para-orto directors?  (Read 1285 times)

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Offline xshadow

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Why halide are para-orto directors?
« on: January 16, 2018, 05:22:49 AM »
I don't understand why halide are parta orto director in  benzene (I know what textbooks say) ,in fact :

A) they are donors of electrons by resonance
B) they are electrons attractor  through inductive effect

Now Inductive effect is much more important in halogen SO why they are para-orto director?!!

In orto,for example,there is a  further resonance structure compared to the meta ( more resonace stabilization  of the positive charge so)

But in ORTO there is also a STRONGER inductive effect that go against the stability of this position(concerning the positve charge  formed in the intermediate  of an electronic aromatic substitution)..AND we know that in halide inductive effect is much important than resonance one

In fact in the " halidephenol" the pka is bigger for the orto position ...i.e. the orto position is much more stable (than follow the meta one) thanks the INDUCTIVE effect...NOT the resonance one that should cause a destablization of the base (donation of electrons stronger in para and orto thanks an additional 4th resonance structure)


Why there is this difference!!
Why orto para directors (so more stabilization/ or, from a different point of view ,less destabliziation of the positive charge  thanks an electron donation by resonance) if inductive effect is much more important than resomance ?! ...the inductive effect is much  important in orto (so less electrons )  as we can see in the stability of the conjugate bases of" halidephenol"


I really don' t  understand this contraddiction..

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