# How come the instability of phenyl cation can be a reason for less reactivity towards nu substitution in aryl compounds

In SN1 mechanism, the formation of carbocation takes place so as much stable is the carbocation that much easy would be the substitution in the compound.
Aryl compounds (like haloarenes) are very less reactive towards nucleophilic substitution. One of the reasons is that the phenyl cation formed is not stabilized by resonance. Since, the phenyl cation is not stable, nucleophilic substitution (
SN1) does not take place.

The phenyl cation does not show resonance. Resonance is the delocalisation of $\pi$-electrons or lone pair electrons. It requires the interacting orbitals to be parallel so they can overlap. The $\pi$-electron cloud of phenyl carbocation is perpendicular to the vacant p-orbital of the carbocation. Therefore no overlap is possible and thus no resonance is possible.

So when in a reaction if an intermediate is not stable then the reaction will not take place. It is very important that any reaction leads to a stabilized intermediates and then products. If stability is not present reaction will not happen.

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