Question

why n nitrophenol is weakest than ortho and para nitrophenol?

Answer 1

Answer:

So, meta nitrophenol is the weakest in terms of acidity. Now, in ortho nitrophenol, intramolecular hydrogen bonding between the adjacent hydroxyl and nitro groups significantly affects the release of the proton. So, it is a weaker acid compared to para nitrophenol.

That's why cresols are less acidic than phenol. One can further realize that the meta compound is more acidic, and this is due to the resonance structures which show a negative charge in ortho and para, but not in meta.

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Answer 2

Explanation:

In substituted phenols, presence of electron withdrawing group (EWG) such as -NO2 group increases the acidic strength of phenol. All nitrophenols are more acidic than phenol. This effect is more pronounced when -NO2 group (EWG) is present at ortho and para positions. Therefore, ortho and para-nitrophenols are more acidic than meta-nitrophenol It is due to the effective delocalisation of negative charge in phenoxide ion.

Note :-

ortho-nitrophenol is less acidic than para-nitrophenol due to intermolecular H-bonding b/w O and H which make loss of a proton more difficult.