Why does Azo coupling of β-naphthol takes place at alpha position and not at gamma position [duplicate]








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[Mechanism of formation of 2-naphthol red dye (aka Sudan 1)](/questions/97067/mechanism-of-formation-of-2-naphthol-red-dye-aka-sudan-1)

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![enter image description here](https://i.stack.imgur.com/DgQYn.jpg)


I have searched for coupling reaction of $\beta$-naphthol with benzene diazonium salt at quite a few places. But everywhere the coupling has been shown at alpha position. Why doesn't it take place at gamma position to minimise steric hindrance.


Chemistry LibreTexts


![enter image description here](https://i.stack.imgur.com/a3K56.jpg)


Chemguide


![enter image description here](https://i.stack.imgur.com/qM7Go.jpg)


My book


![enter image description here](https://i.stack.imgur.com/IWsIP.jpg)




Coupling reaction of β-naphthol with benzene diazonium is an example of electrophilic aromatic substitution.


If the electrophile attacks at alpha position ,then two resonance structures 1 and 2 , with aromatic rings are possible.


[![enter image description here](https://i.stack.imgur.com/XImqZ.png)](https://i.stack.imgur.com/XImqZ.png) 
If the electrophile attacks at gamma position ,only one resonance structures 3 , with aromatic ring is possible and 4 is not aromatic.


[![enter image description here](https://i.stack.imgur.com/Ni3ak.png)](https://i.stack.imgur.com/Ni3ak.png)


Therefore attack at alpha position is the major product.


**References**:


<https://pubs.rsc.org/en/content/articlehtml/2015/gc/c4gc02381a>


<https://en.wikipedia.org/wiki/Azo_coupling>


[Mechanism of formation of 2-naphthol red dye (aka Sudan 1)](https://chemistry.stackexchange.com/questions/97067/mechanism-of-formation-of-2-naphthol-red-dye-aka-sudan-1)


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