[yourdeath01]

I have this reaction of a diazonium salt (p-nitroaniline) was coupled with a phenol (2-napthol) to produce para red dye.

Reaction: https://imgur.com/miUevH4

I am being asked to explain why coupling of p-nitrobezne diazonium chloride occurs mainly at the position that is para to the -n(ch3)2 group of N,N-dimethylaniline but ortho to the -oh group of 2-napthol

Heres my answer to this question: https://imgur.com/7ISeOFE

Another way to answer it: https://imgur.com/OOfaOhp

Basically one set of resonances preserves the aromatic character of the left side ring. The other set doesn’t preserve that character. Which explains why the reaction of diazonium cations occurs at the 1-position but not the 3-position of 2- naphthol.

[pgk]

1). Diazo coupling of N,N-dimethylaniline:
Correct! Diazo coupling of N,N-dimethylaniline occurs at the para-position due to the steric hindrance of the N,N-dimethylamine group.
2). Diazo coupling of 2-napthol:
Wrong! Ortho- coupling occurs under kinetic control, in contrast to the para- and more extended couplings that occur under thermodynamic control. On the other hand, diazo coupling is effectuated at low temperatures < 5 oC. Thus, diazo coupling of the (non-sterically hindered) 2-napthol, is favored at the ortho- position.
Question: Why diazo coupling of 2-napthol is favored at the 1- and not at the 3-position, given that both are ortho- ones?

[pgk]

Answer: This is an issue of Quantum Chemistry but roughly, the p οrbitals of condensed aromatic rings (like 2-naphthol) do nοt equally contribute to the aromatic conjugation (contrary to the benzene ring), which can explain why diazo coupling of 2-naphthol is favored at the 1-position.