Resonance Structures Count for Phenoxide Ion Derived from Beta Naphthol

To determine the total number of contributing resonance structures for the ionic species N ($\beta$-naphtholate ion / 2-naphtholate ion), formed by the reaction of 2-naphthol with $\text{NaOH}$:

$\text{C}_{10}\text{H}_7\text{OH} + \text{NaOH} \rightarrow \text{C}_{10}\text{H}_7\text{O}^- (\mathbf{N}) + \text{H}_2\text{O}$

We count all non-equivalent canonical forms by considering the delocalization of the negative charge across the conjugated system:

1. Structures with the negative charge on the Oxygen atom ($\text{O}^-$): The naphthalene ring framework possesses $3$ distinct Kekulé structures. Since the phenoxide-like oxygen retains a single bond ($\text{C-O}^-$) in these forms, there are: $\text{Number of structures with } \text{O}^- = 3$

2. Structures with the negative charge on Carbon atoms ($\text{C}^-$): By forming a $\text{C=O}$ double bond at position $2$, the negative charge is delocalized onto conjugated ring carbon atoms at ortho, para, and extended conjugated positions:

   • At C-1 (ortho to C-2): $2$ resonance structures (due to two possible distributions of double bonds in the adjacent ring).
   • At C-3 (ortho to C-2): $1$ resonance structure.
   • At C-4 (para to C-2): $1$ resonance structure.
   • At C-6 (extended conjugation): $1$ resonance structure.
   • At C-8 (extended conjugation): $1$ resonance structure.

Summing all canonical contributing structures: $\text{Total number of resonance structures} = 3 \,(\text{on O}) + 2 \,(\text{on C-1}) + 1 \,(\text{on C-3}) + 1 \,(\text{on C-4}) + 1 \,(\text{on C-6}) + 1 \,(\text{on C-8}) = 9$

9