Ortho and para nitrophenols are more acidic than phenol. Draw the resonance structures of the corresponding phenoxide ions.
Ortho and para-nitrophenols are more acidic than phenol due to the presence of the electron withdrawing nitro group. The provided text states that electron withdrawing groups enhance the acidic strength of phenol, and this effect is more pronounced when the group is present at ortho and para positions.
This increased acidity is attributed to the effective delocalisation of negative charge in the phenoxide ion. When the substituent is at the ortho or para position, it allows for the effective dispersal of the negative charge, which stabilises the phenoxide ion. This stability favours the ionisation of phenol. While the phenoxide ion itself involves charge delocalisation, the presence of the nitro group at these specific positions makes the delocalisation more effective compared to phenol. (Note: The specific resonance structures are not provided in the source text).
Explanation
The answer is derived from the textbook context which explains that electron withdrawing groups like the nitro group increase acidity, particularly at ortho and para positions, due to the effective delocalisation of the negative charge in the phenoxide ion. The context mentions that the phenoxide ion is stabilised by delocalisation, but does not explicitly provide the diagrams for the resonance structures of nitrophenoxide ions. Therefore, the answer focuses on the theoretical explanation provided in the text.
Solution Steps
Step 1: Identify that nitro groups are electron withdrawing groups that enhance acidic strength.
Step 2: Note that this effect is most pronounced at ortho and para positions.
Step 3: Explain that this is due to the effective delocalisation of the negative charge in the phenoxide ion, which stabilises it and favours ionisation.