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I am confused,after reading from NCERT text that phenyl cations are unstable due several reasons like the carbon in phenyl group is sp2 hybridized,resonance structures do not stabilizes the phenyl cation.But then,in Fittig reaction we do have phenyl cations as intermediate.For example in a reaction between two molecules of chloro benzene and sodium metal we get a diphenyl molecule.Here we have two phenyl cation generated (if i am right).Then what factor stabilizes the phenyl cation?If there is any error in the theoretical aspect of the question please help me correct it as i am not quite sure about the mechanism.

I would be very much glad to accept an answer with some thermodynamical data like the bond enthalpies of C-Cl bond and newly formed product's bond enthalpy that is C-C bond enthalpy(in the case of diphenyl)and the total realease in energy.

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    $\begingroup$ Then, probably, we don't have phenyl cations as intermediates? $\endgroup$ – Ivan Neretin Feb 24 '16 at 5:45
  • $\begingroup$ @IvanNeretin so what you are saying is that phenyl cations are not being generated?right? – $\endgroup$ – Abhishek P G Feb 24 '16 at 12:00
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    $\begingroup$ The Sandmeyer reaction involves the formation of aryl cations. Although they are very high energy they are formed in this reaction because nitrogen (the leaving group) is also formed in the process. Since nitrogen is an extremely stable molecule it drives the formation of the phenyl cation.. $\endgroup$ – ron Feb 24 '16 at 14:09
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    $\begingroup$ I don't know if the Wurtz reaction involves cations, but the reaction involves solid sodium and complex things can take place on a metal surface. $\endgroup$ – ron Feb 24 '16 at 14:38
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    $\begingroup$ The Wikipedia page for the Wurtz-Fittig reaction suggests the alkyl halide is reduced twice to the organosodium species, which undergoes electrophilic attack on the aryl halide. $\endgroup$ – SendersReagent Feb 24 '16 at 17:19
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The most probable mechanism for Wurtz reaction or Fittig reaction involves formation of organic free radicals and not cations. Like in Wurtz reaction, phenyl free radicals are formed in Fittig too.

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  • $\begingroup$ I checked out the site you mentioned.But it doesn't have any data regarding the mechanism for halobenzene.Rather it has only data regarding aliphatic halides (that is wurtz reaction and not fittig reaction),which probably won't be the answer as both involves completely different type of molecules.One is aromatic and other is aliphatic and C-X bond these two have different bond enthalpy(if i am right). $\endgroup$ – Abhishek P G Feb 24 '16 at 17:11
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    $\begingroup$ Expecting different mechanisms for different molecules is good. However, what is important is in both the cases, Na is used. It is a good reducing agent and can provide electron equally well to aliphatic and aromatic compounds. One more aspect is the C-X bond in aromatic compounds is stronger also implies, X cannot leave as X- $\endgroup$ – adianadiadi Feb 24 '16 at 17:15

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