2-Naphthol is generally considered to be less acidic than phenol. This can be understood by examining the structural characteristics and resonance stabilization of the corresponding anions.
Phenol has a hydroxyl group (-OH) attached to a single benzene ring, which allows for the formation of a phenoxide ion when it donates a proton (H+). The negative charge on the phenoxide ion is stabilized by resonance, allowing it to be delocalized over the aromatic system, making phenol a reasonably strong acid.
On the other hand, 2-naphthol has a hydroxyl group situated on a naphthalene ring, which consists of two fused benzene rings. While it also forms a naphthoxide ion upon deprotonation, the resonance stabilization is somewhat different. In the naphthoxide ion, the negative charge is localized more than in the phenoxide ion, as there are more resonance contributors available due to the larger π-system of the naphthalene. This localization makes the naphthoxide ion less stable compared to the phenoxide ion.
Moreover, 2-naphthol can have additional steric hindrance compared to phenol, which can contribute to its lower acidity. The combination of these factors leads to the conclusion that 2-naphthol is less acidic than phenol due to weaker resonance stabilization of the conjugate base and possibly steric effects.