Arrange in increasing order of pKa values? 1. m-nitro-phenol 2. o-nitro-phenol 3. p-nitro-phenol

1 Answer
Aug 5, 2017

Well, have you quoted the #pK_a# values of the series........?

Explanation:

#"m-nitrophenol"# #;pK_a=8.36#, see this site.

#"o-nitrophenol"# #;pK_a=7.23#, see this site.

#"p-nitrophenol"# #;pK_a=7.15#, see this site.

So why should #"p-nitrophenol"# be more acidic? Well, perhaps because the lone pair of the oxygen is capable of resonance with the quaternized nitrogen centre, a more stable mesomer than that available for #"m-nitrophenol"#; and thus the phenoxide anion, the conjugate base, is less charge-localized, and thus entropically favoured. Anyway you will have to draw out the resonance isomers for each phenoxide, and if it does not make sense, tackle your prof for his interpretation; that is why they pay him/her the big bux..........